ABOUT CHEMISTRY

Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter.^[1]^[2] Chemistry is chiefly concerned with atoms and molecules and their interactions and transformations, for example, the properties of the chemical bonds formed between atoms to create chemical compounds. As such, chemistry studies the involvement of electrons and various forms of energy in photochemical reactions, oxidation-reduction reactions, changes in phases of matter, and separation of mixtures. Preparation and properties of complex substances, such as alloys, polymers, biological molecules, and pharmaceutical agents are considered in specialized fields of chemistry.
Chemistry is sometimes called the central science because it bridges other natural sciences like physics, geology and biology.^[3]^[4] Chemistry is a branch of physical science but distinct from physics.^[5]
The etymology of the word chemistry has been much disputed. The history of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world, particularly the Middle East.^[6]

Etymology

Chemistry

The word chemistry comes from the word alchemy, an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine; it is commonly thought of as the quest to turn lead or another common starting material into gold.^[7] Alchemy, which was practiced around 330, is the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).^[8] An alchemist was called a 'chemist' in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry".
The word alchemy in turn is derived from the Arabic word al-kīmīā (الکیمیاء). In origin, the term is borrowed from the Greek χημία or χημεία.^[9]^[10] This may have Egyptian origins. Many believe that al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian.^[9] Alternately, al-kīmīā may be derived from χημεία, meaning "cast together".^[11]

Definition

In retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term "chymistry", in the view of noted scientist Robert Boyle in 1661, meant the subject of the material principles of mixed bodies.^[12] In 1663, "chymistry" meant a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to a higher perfection - this definition was used by chemist Christopher Glaser.^[13]
The 1730 definition of the word "chemistry", as used by Georg Ernst Stahl, meant the art of resolving mixed, compound, or aggregate bodies into their principles; and of composing such bodies from those principles.^[14] In 1837, Jean-Baptiste Dumas considered the word "chemistry" to refer to the science concerned with the laws and effects of molecular forces.^[15] This definition further evolved until, in 1947, it came to mean the science of substances: their structure, their properties, and the reactions that change them into other substances - a characterization accepted by Linus Pauling.^[16] More recently, in 1998, the definition of "chemistry" was broadened to mean the study of matter and the changes it undergoes, as phrased by Professor Raymond Chang.^[17]

History

Main article: History of chemistry

See also: Alchemy and Timeline of chemistry

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Democritus' atomist philosophy was later adopted by Epicurus (341–270 BCE).

Early civilizations, such as the Egyptians ^[18] and Babylonians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didn't develop a systematic theory.
A basic chemical hypothesis first emerged in Classical Greece with the theory of four elements as propounded definitively by Aristotle stating that that fire, air, earth and water were the fundamental elements from which everything is formed as a combination. Greek atomism dates back to 440 BC, arising in works by philosophers such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura (On The Nature of Things).^[19]^[20] Unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments.^[21]
In the Hellenistic world the art of alchemy first proliferated, mingling magic and occultism into the study of natural substances with the ultimate goal of transmuting elements into gold and discovering the elixir of eternal life.^[22] Alchemy was discovered and practised widely throughout the Arab world after the Muslim conquests,^[23] and from there, diffused into medieval and Renaissance Europe through Latin translations.^[24]

Chemistry as science

Under the influence of the new empirical methods propounded by Sir Francis Bacon and others, a group of chemists at Oxford, Robert Boyle, Robert Hooke and John Mayow began to reshape the old alchemical traditions into a scientific discipline. Boyle in particular is regarded as the founding father of chemistry due to his most important work, the classic chemistry text The Sceptical Chymist where the differentiation is made between the claims of alchemy and the empirical scientific discoveries of the new chemistry.^[25] He formulated Boyle's law, rejected the classical "four elements" and proposed a mechanistic alternative of atoms and chemical reactions that could be subject to rigorous experiment.^[26]

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Antoine-Laurent de Lavoisier is considered the "Father of Modern Chemistry".^[27]

The theory of phlogiston (a substance at the root of all combustion) was propounded by the German Georg Ernst Stahl in the early 18th century and was only overturned by the end of the century by the French chemist Antoine Lavoisier, the chemical analogue of Newton in physics; who did more than any other to establish the new science on proper theoretical footing, by elucidating the principle of conservation of mass and developing a new system of chemical nomenclature used to this day.^[28]
Prior to his work, though, many important discoveries had been made, specifically relating to the nature of 'air' which was discovered to be composed of many different gases. The Scottish chemist Joseph Black (the first experimental chemist) and the Dutchman J. B. van Helmont discovered carbon dioxide, or what Black called 'fixed air' in 1754; Henry Cavendish discovered hydrogen and elucidated its properties and Joseph Priestley and, independently, Carl Wilhelm Scheele isolated pure oxygen.
English scientist John Dalton proposed the modern theory of atoms; that all substances are composed of indivisible 'atoms' of matter and that different atoms have varying atomic weights.
The development of the electrochemical theory of chemical combinations occurred in the early 19th century as the result of the work of two scientists in particular, J. J. Berzelius and Humphry Davy, made possible by the prior invention of the voltaic pile by Alessandro Volta. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current.^[29]
British William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. J. A. R. Newlands devised an early table of elements, which was then developed into the modern periodic table of elements^[30] by the German Julius Lothar Meyer and the Russian Dmitri Mendeleev in the 1860s.^[31] The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table.
Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhler's synthesis of urea which proved that living organisms were, in theory, reducible to chemistry.^[32] Other crucial 19th century advances were; an understanding of valence bonding (Edward Frankland in 1852) and the application of thermodynamics to chemistry (J. W. Gibbs and Svante Arrhenius in the 1870s).

Chemical structure

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Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.
Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge.

At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. In 1897, J. J. Thomson of Cambridge University discovered the electron and soon after the French scientist Becquerel as well as the couple Pierre and Marie Curie investigated the phenomenon of radioactivity. In a series of pioneering scattering experiments Ernest Rutherford at the University of Manchester discovered the internal structure of the atom and the existence of the proton, classified and explained the different types of radioactivity and successfully transmuted the first element by bombarding nitrogen with alpha particles.
His work on atomic structure was improved on by his students, the Danish physicist Niels Bohr and Henry Moseley. The electronic theory of chemical bonds and molecular orbitals was developed by the American scientists Linus Pauling and Gilbert N. Lewis.
The year 2011 was declared by the United Nations as the International Year of Chemistry.^[33] It was an initiative of the International Union of Pure and Applied Chemistry, and of the United Nations Educational, Scientific, and Cultural Organization and involves chemical societies, academics, and institutions worldwide and relied on individual initiatives to organize local and regional activities.

Principles of modern chemistry

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Laboratory, Institute of Biochemistry, University of Cologne.

The current model of atomic structure is the quantum mechanical model.^[34] Traditional chemistry starts with the study of elementary particles, atoms, molecules,^[35] substances, metals, crystals and other aggregates of matter. This matter can be studied in solid, liquid, or gas states, in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory.
The chemistry laboratory stereotypically uses various forms of laboratory glassware. However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it.
A chemical reaction is a transformation of some substances into one or more different substances.^[36] The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal (when unequal, the transformation by definition is not chemical, but rather a nuclear reaction or radioactive decay). The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions. They can be analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists.^[37] Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; some of them are:^[38]

Matter

Main article: Matter

In chemistry, matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles. The particles that make up matter have rest mass as well - not all particles have rest mass, such as the photon. Matter can be a pure chemical substance or a mixture of substances.^[39]

Atom

A diagram of an atom based on the Rutherford model

The atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space called the electron cloud. The nucleus is made up of positively charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively-charged electrons which orbit the nucleus. In a neutral atom, the negatively-charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.^[40]^[41]
The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent).

Element

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Standard form of the periodic table of chemical elements. The colors represent different categories of elements

Main article: Chemical element

A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, but atoms of carbon may have mass numbers of 12 or 13.^[41]
The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number. The periodic table is arranged in groups, or columns, and periods, or rows. The periodic table is useful in identifying periodic trends.^[42]

Compound

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Carbon dioxide (CO₂), an example of a chemical compound

Main article: Chemical compound

A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements.^[43] The standard nomenclature of compounds is set by the International Union of Pure and Applied Chemistry (IUPAC). Organic compounds are named according to the organic nomenclature system.^[44] Inorganic compounds are named according to the inorganic nomenclature system.^[45] In addition the Chemical Abstracts Service has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its CAS registry number.

Molecule

Main article: Molecule

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A ball-and-stick representation of the caffeine molecule (C₈H₁₀N₄O₂).

A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs.
Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a mass spectrometer. Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry.

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A 2-D skeletal model of a benzene molecule (C₆H₆)

The "inert" or noble gas elements (helium, neon, argon, krypton, xenon and radon) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals.
However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite.
One of the main characteristics of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.

Substance and mixture

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Examples of pure chemical substances. From left to right: the elements tin (Sn) and sulfur (S), diamond (an allotrope of carbon), sucrose (pure sugar), and sodium chloride (salt) and sodium bicarbonate (baking soda), which are both ionic compounds.

A chemical substance is a kind of matter with a definite composition and set of properties.^[46] A collection of substances is called a mixture. Examples of mixtures are air and alloys.^{[citation needed]}

Mole and amount of substance

Main article: Mole

The mole is a unit of measurement that denotes an amount of substance (also called chemical amount). The mole is defined as the number of atoms found in exactly 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.^[47] The number of entities per mole is known as the Avogadro constant, and is determined empirically to be approximately 6.022×10²³ mol⁻¹.^[48] Molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in moldm⁻³.^[49]

Phase

Example of phase changes

Main article: Phase

In addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature.
Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.
Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions.
The most familiar examples of phases are solids, liquids, and gases. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water).
Less familiar phases include plasmas, Bose–Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology.

Bonding

Main article: Chemical bond

An animation of the process of ionic bonding between sodium (Na) and chlorine (Cl) to form sodium chloride, or common table salt. Ionic bonding involves one atom taking valence electrons from another (as opposed to sharing, which occurs in covalent bonding)

Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.^[50] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom.
A chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, Valence Bond Theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to explain molecular structure and composition.
An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. For example, sodium (Na), a metal, loses one electron to become an Na⁺ cation while chlorine (Cl), a non-metal, gains this electron to become Cl^-. The ions are held together due to electrostatic attraction, and that compound sodium chloride (NaCl), or common table salt, is formed.

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In the methane molecule (CH₄), the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom (it has eight electrons in its valence shell) and the duet rule is satisfied for the H-atoms (they have two electrons in their valence shells).

In a covalent bond, one or more pairs of valence electrons are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a molecule. Atoms will share valence electrons in such a way as to create a noble gas electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell.
Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals.

Energy

Main article: Energy

In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants.
A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions, the reaction absorbs heat from the surroundings.
Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor $e^{-E/kT}$ - that is the probability of a molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.^[51]
A related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, $\Delta G \le 0 \,$ ; if it is equal to zero the chemical reaction is said to be at equilibrium.
There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions.
The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H₂O); a liquid at room temperature because its molecules are bound by hydrogen bonds.^[52] Whereas hydrogen sulfide (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions.
The transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy.
The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemical spectroscopy, e.g. IR, microwave, NMR, ESR, etc. Spectroscopy is also used to identify the composition of remote objects - like stars and distant galaxies - by analyzing their radiation spectra.

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Emission spectrum of iron

The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances.

Reaction

Main article: Chemical reaction

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During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, a compound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.

When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the 'reaction' of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well with the system environment which may be designed vessels which are often laboratory glassware.
Chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.
A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.^[53]
The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward–Hoffmann rules often come in handy while proposing a mechanism for a chemical reaction.
According to the IUPAC gold book, a chemical reaction is "a process that results in the interconversion of chemical species."^[54] Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events').

Ions and salts

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The crystal lattice structure of potassium chloride (KCl), a salt which is formed due to the attraction of K⁺ cations and Cl^- anions. Note how the overall charge of the ionic compound is zero.

Main article: Ion

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons, the atom is a positively-charged ion or cation. When an atom gains an electron and thus has more electrons than protons, the atom is a negatively-charged ion or anion. Cations and anions can form a crystalline lattice of neutral salts, such as the Na⁺ and Cl^- ions forming sodium chloride, or NaCl. Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH⁻) and phosphate (PO₄³⁻).
Plasma is composed of gaseous matter that has been completely ionized, usually through high temperature.

Acidity and basicity

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When hydrogen bromide (HBr), pictured, is dissolved in water, it forms the strong acid hydrobromic acid

Main article: Acid–base reaction

A substance can often be classified as an acid or a base. There are several different theories which explain acid-base behavior. The simplest is Arrhenius theory, which states than an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid–base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion.
A third common theory is Lewis acid-base theory, which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to this theory, the crucial things being exchanged are charges.^[55]^[^{unreliable source?}^] There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept^[56]
Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the acid dissociation constant (K_a), which measures the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher K_a are more likely to donate hydrogen ions in chemical reactions than those with lower K_a values.

Redox

Main article: Redox

Redox (reduction-oxidation) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons (reduction) or losing electrons (oxidation). Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers.
A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number.

Equilibrium

Main article: Chemical equilibrium

Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase.
A system of chemical substances at equilibrium, even though having an unchanging composition, is most often not static; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time.

Chemical laws

Main article: Chemical law

Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:

Avogadro's law
Beer–Lambert law
Boyle's law (1662, relating pressure and volume)
Charles's law (1787, relating volume and temperature)
Fick's laws of diffusion
Gay-Lussac's law (1809, relating pressure and temperature)
Le Chatelier's principle
Henry's law
Hess's law
Law of conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.
Law of conservation of mass continues to be conserved in isolated systems, even in modern physics. However, special relativity shows that due to mass–energy equivalence, whenever non-material "energy" (heat, light, kinetic energy) is removed from a non-isolated system, some mass will be lost with it. High energy losses result in loss of weighable amounts of mass, an important topic in nuclear chemistry.
Law of definite composition, although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction.
Law of multiple proportions
Raoult's law

Practice

Subdisciplines

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.^[57]

Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry.
Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry is also associated with molecular biology and genetics.
Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.
Materials chemistry is the preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, polymers) and interfaces between different phases.
Neurochemistry is the study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system.
Nuclear chemistry is the study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field.
Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. An organic compound is defined as any compound based on a carbon skeleton.
Physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry.^[58] Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of infinitesimal calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap.
Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) condensed matter physics and molecular physics.

Other disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic (carbon based) matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the study of chemical processes using physical concepts such as thermodynamics and quantum mechanics; and analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines).
Other fields include agrochemistry, astrochemistry (and cosmochemistry), atmospheric chemistry, chemical engineering, chemical biology, chemo-informatics, electrochemistry, environmental chemistry, femtochemistry, flavor chemistry, flow chemistry, geochemistry, green chemistry, histochemistry, history of chemistry, hydrogenation chemistry, immunochemistry, marine chemistry, materials science, mathematical chemistry, mechanochemistry, medicinal chemistry, molecular biology, molecular mechanics, nanotechnology, natural product chemistry, oenology, organometallic chemistry, petrochemistry, pharmacology, photochemistry, physical organic chemistry, phytochemistry, polymer chemistry, radiochemistry, solid-state chemistry, sonochemistry, supramolecular chemistry, surface chemistry, synthetic chemistry, thermochemistry, and many others.

Chemical industry

Main article: Chemical industry

The chemical industry represents an important economic activity. The global top 50 chemical producers in 2004 had sales of 587 billion US dollars with a profit margin of 8.1% and research and development spending of 2.1% of total chemical sales.^[59]

Physical and chemical change

Chemistry: [ Back ] [ Next ] Home

Chemical change Physical change The three states of matter Change in Mass

In a physical change no new substance is formed
Examples of physical change are: evaporation, melting, freezing and condensation.
Physical changes are usually temporary and can often be reversed

In a chemical change a chemical reaction is taking place and a new substance is always formed
Examples of chemical change are decomposition, oxidation and combustion.
Chemical changes are usually permanent and cannot easily be reversed.

Table to show the effect of heat on some chemicals

Chemical	Appearance	Effect of heat	Type of change	Change in mass when heated.
Magnesium ribbon	Grey metal	Burns with an intense white flame to leave a white ash called magnesium oxide.	Permanent	Gain because it combines with oxygen from the air
Copper foil	Pink metal	Forms a layer of black copper oxide on the surface.	Permanent	Gain because it combines with oxygen from he air.
Hydrated cobalt chloride	pink/purple crystals	Turned to a blue powder called anhydrous cobalt chloride and gave off water vapour. The blue powder gradually turned pink again when it was left standing in the room.	Reversible chemical change. Often used as a test for water *	Loss because it loses water vapour.
Potassium permanganate	dark purple/black crystals	Decomposes and produces oxygen gas	Permanent	Loss because it loses water vapour
Calcium carbonate (chalk, limestone)	White solid	Decomposes, producing carbon dioxide gas and leaving a white solid called calcium oxide (lime)	permanent†	Loss because it loses carbon dioxide
Hydrated copper sulphate	Blue crystals	Turned to a white powder called anhydrous copper sulphate and produced water vapour.	Reversible chemical change.	Loss because it loses water vapour.
Zinc oxide	White powder	Turned yellow when hot and white when cold.	Temporary	No change.
Iodine	Dark grey/purple crystals	Forms a purple vapour which turns back to grey iodine crystals when it cools.	Temporary	No change because all of the iodine vapour turns back to solid iodine crystals.
Copper carbonate	Green Powder	Decomposes. Evolves carbon dioxide gas and leaves a black residue of copper oxide.	Permanent	Loss because it gives out carbon dioxide gas.

*Test for the presence of water: Water can be identified by placing it onto blue cobalt chloride paper which will turn pink

†Calcium carbonate can be obtained from lime by dissolving the lime in water, filtering and blowing carbon dioxide through the filtrate.

Types of change that could occur when a single substance is heated:
The change could either be PHYSICAL or CHEMICAL.

A chemical change always produces a new substance and is usually permanent.
A physical change forms no new chemical and is usually temporary.

CHEMICAL CHANGE

The following are types of chemical change because in each case a new substance is formed

1. Decomposition
This is when a compound splits apart into two (or more) chemicals.

eg: copper carbonate decomposes when heated to form carbon dioxide gas and leave black copper oxide.

Word equation: Copper carbonate ---------> copper oxide + carbon dioxide

2. Oxidation
: When a chemical combines (joins up with) oxygen to form an oxide.

eg copper foil will oxidise when heated strongly in air

Word equation: copper + oxygen -------> copper oxide

3. Combustion (or burning) is a kind of oxidation where a flame is usually produced.

eg Magnesium will burn in air to form magnesium oxide:

Word equation: Magnesium + oxygen -------> magnesium oxide

Signs for a chemical change are:

1. A change in colour ( eg changes from pink to blue)

2. A change in temperature (eg gets warm or hot)

Physical change

All of the terms described below are types of physical change because no new substance is made and the changes are all reversible

getting hotter:
MELTING : When a solid turns to a liquid. This happen as soon as the substance reaches (or goes above) a temperature called its melting point
eg WAX melts when heated.

EVAPORATING: When a liquid turns to a vapour

BOILING: This is when a liquid turns to a vapour at its boiling point.
eg WATER boils when heated.

SUBLIMING : This is when a solid turns to a vapour without becoming a liquid
eg IODINE turns from a solid to a purple vapour when heated

Getting colder
CONDENSING: This is when a vapour turns to a liquid when it is cooled down (to below the boiling point)

FREEZING (or solidifying): This is when a liquid turns to a solid. This happens when the liquid cools to below its melting point.

SUBLIMING : This is when a vapour turns to a solid without becoming a liquid
eg IODINE turns from a purple vapour to a black solid when heated

[notice that the same word (subliming) is used for the change from a solid to a vapour and from a vapour to a solid]

The Three States of Matter
The three states, SOLID, LIQUID and GAS are called the three states of matter (see Kinetic Theory)

The boiling point of a substance is the temperature that causes it to change from a liquid to a gas

At a temperature ABOVE its boiling point a substance will always be a gas

The melting point of a substance is the temperature that causes it to change from a solid to a liquid

At a temperature below its melting point a substance will always be a solid

At a temperature between its melting point and boiling point it will be a liquid

Substance	Melting point	Boiling point	State at room temperature
Lead	327	1740	Solid
Mercury	-39 C	357 C	Liquid
Oxygen	-218	-183	Gas

You don't need to remember the melting points and boiling points but you DO need to know why each substance is a solid, liquid or gas.

You DO need to know the melting point and boiling point of water
Water:

Boiling point = 100 C
Melting point = 0 C

We can make a substance change state by heating it up or cooling it down as described below.

The Change in Mass when a chemical is heated

When certain elements are heated like magnesium or copper they will gain in mass. (See table above)
They do this because they combine with oxygen.

To find out if there is a change in mass the chemical needs to be weighed before and after heating.

Example 1: Copper foil will gain in mass when heated in air because the copper oxidises (combines with oxygen)
Word equation: copper + oxygen -------> copper oxide

Example 2: Magnesium will gain in mass when it burns because the magnesium combines with oxygen however care must be taken to make sure that the smoke produced all gets weighed (See Burning Magnesium).

When compounds that decompose are heated they will often LOSE mass

Example 1: When copper sulphate is heated it will lose mass because it decompose and give off water vapour. (See experiment to heat copper sulphate)

Example 2: When Copper carbonate is heated it will lose mass because it decomposes and gives off carbon dioxide gas.

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Does Copper React with Acid?

Copper is an unreactive metal that does not normally react with acids. However, it reacts with nitric acid. This is because, nitric acid is a very strong oxidizing agent.

Clean copper metal will not react with any acid, unless the acid is also an oxidising agent. This is because copper is below hydrogen in the activities series. (If you are very smart, you will notice that this is not really an explanation, just an impressive way of saying that copper is not reactive enough to react with acids.)

If the copper surface has been oxidised, the copper oxide will dissolve in acid.

If the acid is strongly oxidising, the copper can dissolve to make a solution of the copper salt. For example, copper dissolves in concentrated nitric acid to give you nitrogen oxides and copper nitrate in solution, and also in hot concentrated sulphuric acid to give you sulphur dioxide and copper hydrogensulphate in solution.

How does copper react with nitric acid?

September 15, 2008 Charco

Copper is an unreactive metal and doesn’t react in normal circumstances with dilute acids. However it does react with nitric acid. Why is this?

Nitric acid is an oxidising agent and the reaction is not the usual acid + metal reaction. The products are oxides of nitrogen instead of hydrogen. The actual nitrogen oxide formed depends on the concentration and temperature of the acid.

There are actually two equations for the reaction of copper with nitric acid. It depends on whether the nitric acid is concentrated or not. If it is concentrated and in excess then the ratio is 1:4 copper to nitric acid. If it is dilute then the ratio is 3:8.

Cu + 4HNO₃ –> Cu(NO₃)₂ + 2NO₂ + 2H₂O

3Cu + 8HNO₃ –> 3Cu(NO₃)₂ + 2NO + 4H₂O

Nitric acid when concentrated is a strong oxidising agent so it makes sense that a higher oxidation state of nitrogen (IV) oxide is formed when the nitric acid is concentrated.

Scientific Method Steps

Learn the Steps of the Scientific Method

By Anne Marie Helmenstine, Ph.D.

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6 Steps of the Scientific Method

Scientific Method Steps

By Anne Marie Helmenstine, Ph.D.

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The scientific method is a system for asking and answering questions.

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The scientific method is a systematic way of learning about the world around us and answering questions. The number of steps varies from one description to another, mainly when data and analysis are separated into separate step, but this is a fairly standard list of 6 scientific method steps, which you are expected to know for any science class:

Purpose/Question
Ask a question.
Research
Conduct background research. Write down your sources so you can cite your references.
Hypothesis
Propose a hypothesis. This is a sort of educated guess about what you expect. (see examples)
Experiment
Design and perform an experiment to test your hypothesis. An experiment has an independent and dependent variable. You change or control the independent variable and record the effect it has on the dependent variable.
Data/Analysis
Record observations and analyze what the data means. Often, you'll prepare a table or graph of the data.
Conclusion
Conclude whether to accept or reject your hypothesis. Communicate your results.

What Are Examples of a Hypothesis?

By Anne Marie Helmenstine, Ph.D.

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Propose a hypothesis before designing and conducting an experiment.

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Examples of the Null Hypothesis

Hyperactivity is unrelated to eating sugar.
All daisies have the same number of petals.
The number of pets in a household is unrelated to the number of people living in it.
A person's preference for a shirt is unrelated to its color.

Examples of an If, Then Hypothesis

If you get at least 6 hours of sleep, you will do better on tests than if you get less sleep.
If you drop a ball, it will fall toward the ground.
If you drink coffee before going to bed, then it will take longer to fall asleep.
If you cover a wound with a bandage, then it will heal with less scarring.

Improving a Hypothesis To Make It Testable

While there are many ways to state a hypothesis, you may wish to revise your first hypothesis in order to make it easier to design an experiment to test it. For example, let's say you have a bad breakout the morning after eating a lot of greasy food. You may wonder if there is a correlation between eating greasy food and getting pimples. You propose a hypothesis:

Eating greasy food causes pimples.
Next you need to design an experiment to test this hypothesis. Let's say you decide to eat greasy food every day for a week and record the effect on your face. Then, as a control, for the next week you'll avoid greasy food and see what happens. Now, this is not a very good experiment because it does not take into account other factors, such as hormone levels, stress, sun exposure, exercise or any number of other variables which might conceivably affect your skin. The problem is that you cannot assign cause to your effect. If you eat french fries for a week and suffer a breakout, can you definitely say it was the grease in the food that caused it? Maybe it was the salt. Maybe it was the potato. Maybe it was unrelated to diet.You can't prove your hypothesis. It's much easier to disprove a hypothesis. So, let's restate the hypothesis to make it easy to evaluate the data.
Getting pimples is unaffected by eating greasy food.
So, if you eat fatty food every day for a week and suffer breakouts and then don't breakout the week that you avoid greasy food, you can be pretty sure something is up. Can you disprove the hypothesis? Probably not, since it is so hard to assign cause and effect. However, you can make a strong case that there is some relationship between diet and acne.
If your skin stays clear for the entire test, you may decide to accept your hypothesis. Again, you didn't prove or disprove anything, which is fine.

Elements of a Good Hypothesis

What Makes a Good Experimental Hypothesis?

By Anne Marie Helmenstine, Ph.D.

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A hypothesis is an educated guess or prediction of what will happen. In science, a hypothesis proposes a relationship between factors called variables. A good hypothesis relates an independent variable and a dependent variable. The effect on the dependent variable depends on or is determined by what happens when you change the independent variable. While you could consider any prediction of an outcome to be a type of hypothesis, a good hypothesis is one you can test using the scientific method. In other words, you want to propose a hypothesis to use as the basis for an experiment.
Cause and Effect or If, Then Relationships
A good experimental hypothesis can be written as an "if, then" statement to establish cause and effect on the variables. If you make a change to the independent variable, then the dependent variable will respond. Here's an example of a hypothesis:
If you increase the duration of light, corn plants will grow more each day.
The hypothesis establishes two variables, length of light exposure and rate of plant growth. An experiment could be designed to test whether rate of growth depends on duration of light. The duration of light is the independent variable, which you can control in an experiment. The rate of plant growth is the dependent variable, which you can measure and record as data in an experiment.
Checklist for a Good Hypothesis
When you have an idea for a hypothesis, it may help to write it several different ways. Review your choices and select a hypothesis that accurately describes what you are testing.

Does the hypothesis relate an independent and dependent variable? Can you identify the variables?
Can you test the hypothesis? In other words, could you design an experiment that would allow you to establish or disprove a relationship between the variables?
Would your experiment be safe and ethical?
Is there a simpler or more precise way to state the hypothesis? If so, rewrite it.

What If the Hypothesis Is Incorrect?
It's not wrong or bad if the hypothesis is not supported or is incorrect. Actually, this outcome may tell you more about a relationship between the variables than if the hypothesis is supported. You may intentionally write your hypothesis as a null hypothesis or no-difference hypothesis to establish a relationship between the variables.
For example, the hypothesis:
The rate of corn plant growth does not depend on the duration of light.
... can be tested by exposing corn plants to different length "days" and measuring the rate of plant growth. A statistical test can be applied to measure how well the data supports the hypothesis. If the hypothesis is not supported, then you have evidence of a relationship between the variables. It's easier to establish cause and effect by testing whether "no effect" is found. Alternatively, if the null hypothesis is supported, then you have shown the variables are not related. Either way, your experiment is a success.
Hypothesis Examples
Need more examples of how to write a hypothesis? Here you go:

If you turn out all the lights, you will fall asleep faster. (Think: How would you test it?)
If you drop different objects, they will fall at the same rate.
If you eat only fast food, then you will gain weight.
If you use cruise control, then your car will get better gas mileage.
If you apply a top coat, then your manicure will last longer.
If you turn the lights on and off rapidly, then the bulb will burn out faster.

Mixtures

A mixture is made from different substances that are not chemically joined.
For example powdered iron and powdered sulphur mixed together makes a mixture of iron and sulphur. They can be separated from each other without a chemical reaction, in the way that different coloured sweets can be picked out from a mixed packet and put into separate piles.

A mixed pile of sweets is separated into 4 piles of different colours - red, green, yellow and purple

Mixture and compounds

Mixtures have different properties from compounds. The table summarises these differences.

	Mixture	Compound
Composition	Variable composition – you can vary the amount of each substance in a mixture.	Definite composition – you cannot vary the amount of each element in a compound.
Joined or not	The different substances are not chemically joined together.	The different elements are chemically joined together.
Properties	Each substance in the mixture keeps its own properties.	The compound has properties different from the elements it contains.
Separation	Each substance is easily separated from the mixture.	It can only be separated into its elements using chemical reactions.
Examples	Air, sea water, most rocks.	Water, carbon dioxide, magnesium oxide, sodium chloride.

An example - iron, sulphur and iron sulphide

Remember that iron and sulphur react together when they are heated to make a compound called iron sulphide. What are the differences between a mixture of iron and sulphur, and iron sulphide? Here are some of them:

· The mixture can contain more or less iron, but iron sulphide always contains equal amounts of iron and sulphur.

· The iron and sulphur atoms are not joined together in the mixture, but they are joined together in iron sulphide.

· The iron and sulphur still behave like iron and sulphur in the mixture, but iron sulphide has different properties from both iron and sulphur.

· You can separate the iron from the mixture using a magnet but this does not work for iron sulphide.

Separating mixtures

The different substances in mixtures are usually easily separated from one another. The method you use depends upon the type of mixture you have.

Chromatography

This is good for separating dissolved substances that have different colours, such as inks and plant dyes. It works because some of the coloured substances dissolve in the liquid better than others, so they travel further up the paper.

Separating dissolved substances

A pencil line is drawn, and spots of ink or plant dye are placed on it. There is a basin containing solvent

Separating dissolved substances

The paper is lowered into the solvent. Some of the dyes or inks have started to spread further up the paper.

Separating dissolved substances

The paper has absorbed the solvent, and the ink or plant dye has spread further up the paper. The colours are now yellow, red and black.

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Filtration

Filtration is good for separating an insoluble solid from a liquid. (An insoluble substance is one that does not dissolve).
Sand, for example, can be separated from a mixture of sand and water using filtration. That's because sand does not dissolve in water.

Separating insoluble solids

Shows a beaker with a mixture of solid and liquid in it. Another beaker has a funnel with some filter paper in.

Separating insoluble solids

The solid and liquid mxture is poured into the filter funnel

Separating insoluble solids

The liquid can drip through the filter paper into the beaker below, but the solid particles can't. They are caught in the filter paper.

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Evaporation

This is good for separating a soluble solid from a liquid (a soluble substance does dissolve, to form a solution).
For example copper sulphate crystals can be separated from copper sulphate solution using evaporation. Remember that it is the water that evaporates away, not the solution.

Separating a soluble solid

A solution is placed in an evaporating basin and heated with a bunsen burner.

Separating a soluble solid

The amount of the solution has reduced as some has evapourated. Small particles can be seen at the bottom of the basin containing the solution.

Separating a soluble solid

The solution has evapourated, leaving a crystalised solute

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Simple distillation

This is good for separating a liquid from a solution. For example, water can be separated from salty water by simple distillation. This method works because the water evaporates from the solution, but is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.

Separating a liquid from a solution

Separating a liquid from a solution

Salty water is heated, and water evapourates. The water vapour cools in the condenser and drips into a beaker.

Separating a liquid from a solution

All the water has evapourated from the salty water, leaving just salt. The water has condensed and is now in the beaker.

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Fractional distillation

This is good for separating two or more liquids from each other. For example, ethanol (alcohol) can be separated from a mixture of ethanol and water by fractional distillation. This method works because the two liquids have different boiling points.

Separating two or more liquids

Water and ethanol solution are heated in a flask over a bunsen burner, pure vapour is produced in the air above the solution within the flask.

Separating two or more liquids

temperature reaches 78 degrees celcius, vapour condenses in a condenser, ethanol drips out into a beaker

The ethanol reaches boiling point andstarts to evaporate.

Separating two or more liquids

Water and ethanol solution has reached 100 degrees celcius. pure water now drips into the beaker, from the test tube.

The ethanol has evaporated, and the water vapour has been cooled and condensed.

Water and ethanol solution is heated.

Compounds

Atoms of different elements can join together in chemical reactions to form compounds. For example hydrogen and oxygen are elements. They react together to form water, a compound.
There are countless different ways for the elements to join together, and millions of compounds are known.

Properties of compounds

The properties of compounds are usually very different from the properties of the elements they contain. For example hydrogen and oxygen are both gases at room temperature, but water is a liquid.
The reaction between iron and sulphur to make iron sulphide is often used in school to study elements and compounds. Look at the animation to remind you what happens in this reaction.

Creating iron sulphide

A test tube filled with a mixture of iron and sulfur

A test tube is filled with a mixture of iron and sulfur.

Creating iron sulphide

The mixture is heated. There are 3 different coloured layers. The top layer is green-yellow, the original colour of the mixture. The second layer is red-orange. The bottom layer, closest to the flame, is dark grey.

The test tube is heated using a bunsen burner.

Creating iron sulphide

The mixture turns to iron sulfide, shown by a dark grey colour

The mixture is now a compound called iron sulfide.

The table compares the properties of iron and sulphur (the two elements), and iron sulphide (the compound).

	Element	Element	Compound
	iron	sulphur	iron sulphide
colour	silvery grey	yellow	black
is it attracted to a magnet?	yes	no	no
reaction with hydrochloric acid	hydrogen formed	no reaction	smelly hydrogen sulphide formed

Chemical bonds

The atoms in a compound are chemically joined together by strong forces called bonds. You can only separate the elements in a compound using another chemical reaction. Separation methods like filtration and distillation will not do this.

Compounds form when atoms join together in a chemical reaction

Chemical formulae

Remember that we use chemical symbols to stand for the elements. For example, C stands for carbon, O stands for oxygen, S stands for sulphur and Na stands for sodium. For a molecule we use the chemical symbols of the atoms it contains to write down its formula.
For example the formula for carbon monoxide is CO. It tells you that each molecule of carbon monoxide consists of one carbon atom joined to one oxygen atom.
Take care when writing your symbols and formulae. Be careful about when to use capital letters. For example CO means a molecule of carbon monoxide but Co is the symbol for cobalt.

Formula and formulae

The word 'formulae' ("form-u-lee") is the plural of 'formula'. If we have more than one formula, we don't say formulas, we say formulae.

Numbers in formulae

If the molecule contains more than one atom of an element we use numbers to show this. The numbers are written below the element symbol. For example, the formula for carbon dioxide is CO₂ . It tells you that each molecule has one carbon atom and two oxygen atoms.
Take care when writing these formulae. The small number go at the bottom. For example CO₂ is correct but CO² is wrong.
Some formulae are more complicated. For example, the formula for sodium sulphate is Na₂SO₄ . It tells you that sodium sulphate contains two sodium atoms (Na₂ ), one sulphur atom (S) and four oxygen atoms (O₄ ).

There are 2 sodium (Na) atoms, one sulfur (S) atom, and 4 oxygen (O) atoms

Formulae are always the same

All compounds have a definite composition. Let's look at water as an example. A water molecule always has two hydrogen atoms and one oxygen atom - it cannot be a water molecule if it has different numbers of these atoms. Its formula is always H₂O.

The reactivity series

Reactive and unreactive

Magnesium burns very brightly when heated in air

Some metals are very unreactive. That means they do not easily take part in chemical reactions. For example platinum does not react with oxygen in the air, even if it is heated in a Bunsen burner flame.
Some metals are very reactive. They easily take part in chemical reactions to make new substances.
Magnesium is like this. If it is heated in a Bunsen burner, it ignites and burns with a brilliant white flame.

Putting metals in order of reactivity

Lists from most reactive to least reactive - potassium, sodium, calcium, magnesium, aluminium, zinc, iron, tin, lead, copper, silver, gold, platinum.

The reactivity series for some common metals

Metal and non-metals oxides

Reaction with oxygen

Remember that metals react with oxygen in the air to produce metal oxides, like magnesium oxide.
Non-metals react with oxygen in the air to produce non-metal oxides. Here are two examples for the non-metals carbon and sulphur.

Carbon burns in air to form carbon dioxide:
carbon + oxygen → carbon dioxide

Sulphur burns in air to form sulphur dioxide:
sulphur + oxygen → sulphur dioxide

Non-metal oxides such as sulphur dioxide and nitrogen oxide are responsible for acid rain. They dissolve in the water in the clouds to form acidic solutions. Acid rain damages rocks and buildings, and harms wildlife.

Differences between metal oxides and non-metal oxides

There are some important differences between the physical and chemical properties of metal oxides and non-metal oxides. The table shows some of these differences.

Metal oxides	Non-metal oxides
solids at room temperature	usually gases at room temperature
bases – if they dissolve they form alkaline solutions	dissolve in water to form acidic solutions

Particle model

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You can use the idea of particles to explain the properties of solids, liquids and gases.The strength of bonds between particles is different in all three states. It explains why solids cannot flow, and why gases can be compressed.

Introduction

This Revision Bite covers:

· Solids

· Liquids

· Gases

· Flowing

· Arrangement and movement

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Solids

Steel, plastic and wood are solids at room temperature. Ice is solid water.
The particles in a solid have the following characteristics:

· they are close together

· they are arranged in a regular pattern

· they are held together by strong forces called bonds

· they can vibrate in a fixed position

· they cannot move from place to place

The table shows some of the properties of solids and why they are like this.

Property of solids	Why they are like this
They have a fixed shape and cannot flow.	The particles cannot move from place to place.
They cannot be compressed or squashed.	The particles are close together and have no space to move into.

Liquids

Mercury, lemonade and water are liquids at room temperature.

The particles in a liquid are:

close together
arranged in a random way

The particles in a liquid can:

move around each other

The bonds in a liquid are strong enough to keep the particles close together, but weak enough to let them move around each other.

The table shows some of the properties of liquids and why they are like this.

Property of liquids	Why they are like this
They flow and take the shape of their container.	The particles can move around each other.
They cannot be compressed or squashed.	The particles are close together and have no space to move into.

Gases

Air, helium and chlorine are gases at room temperature. Water vapour is water as a gas.

The particles in a gas are:

far apart
arranged in a random way

The particles in a gas can:

move quickly in all directions

There are no bonds between the particles in a gas, so they are free to move in any direction.

The table shows some of the properties of gases and why they are like this.

Property of gases	Why they are like this
They flow and completely fill their container.	The particles can move quickly in all directions.
They can be compressed or squashed.	The particles are far apart and have space to move into.

Flowing

Liquids and gases do not have a fixed shape. They can flow and fill their containers, but solids cannot. The particle model explains why.

Solids

Solids cannot flow because their particles are only able to vibrate and cannot move from place to place.

Liquids

Liquids can flow because their particles can move over each other. When water is poured into a glass, the particles of water move over each other and into the corners of the glass. The particles keep on moving over each other as the water takes the shape of the glass. The animation shows how this works.

Gases

Gases can flow because their particles can move in all directions. When a Bunsen burner is connected to a gas tap and turned on, natural gas flows through the rubber tubing. The particles of natural gas are free to move anywhere inside the tubing, and pressure forces them through the tubing into the Bunsen burner.

Arrangement and movement

The table summarises the arrangement and movement of the particles in solids, liquids and gases. It also shows simple diagrams of the arrangement of the particles that you should be able to draw and recognise.

	Solid	Liquid	Gas
Arrangement of particles	Close together Regular pattern	Close together Random arrangement	Far apart Random arrangement
Movement of particles	Vibrate on the spot	Move around each other	Move quickly in all directions
Diagram

Atoms and elements

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Everything is made from atoms, and there are over 100 different types. These are called elements, and they can be divided into the metals and the non-metals. We'll look at their physical and chemical properties in this Revision Bite.

Introduction

This Revision Bite covers:

· Atoms

· Chemical symbols

· The periodic table

· Metals

· Non-metals

· Metals v non-metals

Atoms and elements

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Atoms

Everything is made from atoms, including you. Atoms are tiny particles that are far too small to see, even with a microscope. If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across!
We usually imagine atoms as being like tiny balls:

To make diagrams simpler we often draw atoms as circles:

Elements

There are over a hundred different types of atom, and these are called elements. Each element has a special name. For example carbon, oxygen and hydrogen are all elements.
Lead and gold are elements too. A piece of pure gold contains only gold atoms. A piece of pure lead contains only lead atoms.
Chemical reactions join or split atoms to rearrange them. But they cannot change one element into another element, or anything simpler. A chemical reaction cannot turn lead into gold, becuse it can't change the atoms into different elements.

Atoms and elements

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Chemical symbols

Each element is given its own chemical symbol, like O for oxygen and Cl for chlorine. Chemical symbols are usually one or two letters long, but sometimes three letters are used.
Every chemical symbol starts with a capital letter, with the second or third letters written in lower case.
For example, Mg is the correct symbol for magnesium, but mg, mG and MG are wrong.
Take care to write chemical symbols correctly

Mg	mg	mG	MG

Symbols and names

Sometimes it is easy to tell which element a symbol stands for. For example, O stands for oxygen and Li stands for lithium.
But sometimes the symbol comes from a name for the element that is not an English word.For example, W stands for tungsten (from the word wolfram) and Na stands for sodium (from the word natrium).
The reason is that the same chemical symbols are used all over the world, no matter which language is spoken, which makes them most useful.

The periodic table

All the different elements are arranged in a chart called the periodic table.

· The horizontal rows are called periods.

· The vertical columns are called groups.

· Elements in the same group are similar to each other.

· The metals are on the left and the non-metals are on the right.

· One non-metal, hydrogen, is often put in the middle.

· The main groups are numbered from 1 to 7 going from left to right, and the last group on the right is group 0.

The periodic table

The zig-zag line in this diagram separates the metals, on the left, from non-metals, on the right. Hydrogen is a non-metal but it is often put in the middle.
Notice that most elements are metals, rather than non-metals.
Each element has its own chemical symbol, made from letters. Remember that you will only find elements in the periodic table and never compounds. So don't try to look for substances like water and copper sulphate in the periodic table, because they are not there.

Metals

Iron, magnesium and gold are examples of metal elements.
All metals have these properties in common:

· They are shiny, especially when they are freshly cut.

· They are good conductors of both heat and electricity.

· They can be bent without breaking (they are malleable).

Most metals also have these properties:

· they are solid at room temperature, except mercury, which is liquid at room temperature

· they are hard and strong

· they have a high density (they feel heavy for their size)

· they make a ringing sound when they are hit (they are sonorous)

Mercury is the only metal that is liquid at standard room temperature and pressure

Mercury is the only liquid metal at room temperature.
Three metals are magnetic.
These are iron, cobalt and nickel. Steel is a mixture of elements but mostly iron, so it is also magnetic. The other metals are not magnetic.

Uses of metals

You may have to match the use of a metal with a property that makes it suitable for that use. For example, copper is used for electrical wiring because it is a good conductor of electricity, not because it is a good conductor of heat.

Non-metals

Oxygen, carbon, sulphur and chlorine are examples of non-metal elements.
All non-metals have these properties in common:

· they are dull (not shiny)

· they are poor conductors of heat and electricity (they are insulators)

· they are weak and brittle (they easily break or shatter)

Most non-metals have these properties:

· they have a low density (they feel light for their size)

· they do not make a ringing sound when they are hit (they are not sonourous)

Eleven non-metals are gases at room temperature, including oxygen and chlorine.
One non-metal, bromine, is a liquid at room temperature.
The other non-metals are solids at room temperature, including carbon and sulphur.

Curious carbon

Carbon is a solid non-metal element. Pure carbon can exist in two very different forms - diamond and graphite. The table shows some differences between them.

Diamond	Graphite
transparent and colourless	opaque and black
hard	soft

Diamonds are used in jewellery

Diamond is the hardest natural substance on Earth, but it is also very brittle and will shatter if hit with a hammer.
Graphite is unusual because it is a non-metal that conducts electricity.
Diamonds are used in jewellery

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Metals v non-metals

Remember that most elements are metals, rather than non-metals. The table summarises some differences in their properties.

Properties

Properties of metals and non metals

Property	Metals	Non-metals
Appearance	Shiny	Dull
State at room temperature	Solid (except mercury, which is a liquid)	About half are solids, about half are gases, and one (bromine) is a liquid
Density	High (they feel heavy for their size)	Low (they feel light for their size)
Strength	Strong	Weak
Malleable or brittle	Malleable (they bend without breaking)	Brittle (they break or shatter when hammered)
Conduction of heat	Good	Poor (they are insulators)
Conduction of electricity	Good	Poor (they are insulators, apart from graphite)
Magnetic material	Only iron, cobalt and nickel	None
Sound when hit	They make a ringing sound (they are sonorous)	They make a dull sound

Telling them apart

Notice that metals and non-metals have opposite properties to each other. It is usually easy to tell metals and non-metals apart, but some tests are more reliable than others
For example using a magnet is not a good test to see if an element is a metal. That's because only three metals are magnetic, not all of them.

Acids, bases and metals

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Acids, bases, alkalis and metals are found in the laboratory and at home. They can be irritant or corrosive and must be handled carefully.
How acid or alkaline a chemical is can be measured on the pH scale, using indicators like litmus and universal indicator. Acids and bases react together to form salts and other products too.

Introduction

This Revision Bite covers:

· Acids in the laboratory

· Bases and alkalis

· Indicators and the pH scale

· Reactions of acids with bases

· Naming salts

· Reactions of acids with metals

Acids, bases and metals

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Dilute acids

You will have used some dilute acids at school, such as hydrochloric acid, sulphuric acid and nitric acid. Their bottles are labelled with the warning symbol for 'irritant'.
This means that if any of them makes contact with your skin, it will become red or blistered. You must wash off any spills with plenty of water, otherwise your skin will soon feel as if it is burning.

Concentrated acids

Two test tubes dripping liquid onto two objects. Where the objects have come into contact with the liquids, they have corroded

You are unlikely to have used concentrated acids but your teacher might have shown you some experiments with them. This is because concentrated acids are corrosive. They can attack metals and destroy skin if spilled.

Acids in the home

Laboratory acids are far too dangerous to taste, but you will have swallowed some dilute weak acids. Acids have a sour taste, like vinegar, which contains ethanoic acid, and lemons, which contain citric acid. These are safe to use in food, but they can still hurt if they get into a cut or into your eyes.
Other acids you will find at home are carbonic acid in fizzy drinks, tannic acid in tea and ascorbic acid which is vitamin C, found in fruit and vegetables.

Source	Acid
Vinegar	Ethanoic acid
Fizzy drinks	Carbonic acid
Tea	Tannic acid
Vitamin C	Ascorbic acid
Lemons	Citric acid

Bases and alkalis

Bases v alkalis

Bases are substances that react with acids and neutralise them. They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates. Many bases are insoluble - they do not dissolve in water.
If a base does dissolve in water, we call it an alkali.
Here are two examples:

· Copper oxide is a base because it will react with acids and neutralise them, but it is not an alkali because it does not dissolve in water.

· Sodium hydroxide is a base because it will react with acids and neutralise them. It's also an alkali because it dissolves in water.

Shows a large red circle representing bases. Within this is a smaller grey circle representing alkalis.

All alkalis are bases, but only soluble bases are alkalis

Bases in the laboratory

You will have used some strong bases and alkalis at school, such as sodium hydroxide solution. Like acids, their bottles are labelled with the warning symbol for 'irritant'. This means that they will make your skin red or blistered unless you wash off any spills with plenty of water.
Alkalis feel soapy when they get on your skin, so it is easy to tell when you have had an accident and must wash your hands.
Concentrated alkalis are corrosive. They can attack metals and destroy skin if spilled. They are just as dangerous as concentrated acids, but many people do not realise this.

Bases in the home

Bases react with oils and fats, so they are often used in strong household cleaners. Drain cleaners and oven cleaners usually contain sodium hydroxide for example. And ammonia is also commonly used in cleaners. Ammonia can be recognised by its choking smell.
It is wise to wear gloves when using these substances, otherwise they will react with your skin and burn it.
Weak bases and alkalis are found in toothpaste, antacid tablets (to help cure an upset stomach) and baking powder.

Indicators and the pH scale

When an acid is dissolved in water we get an acidic solution, and alkalis make alkaline solutions. If a solution is neither acidic nor alkaline we call it neutral. Pure water is neutral, and so is paraffin.
Indicators are substances that change colour when they are added to acidic or alkaline solutions. You can prepare homemade indicators from red cabbage or beetroot juice - these will help you see if a solution is acidic or alkaline.
Litmus and universal indicator are two indicators that are commonly used in the laboratory.

Litmus

Litmus indicator solution turns red in acidic solutions and blue in alkaline solutions - and it turns purple in neutral solutions.
Litmus paper is usually more reliable, and comes as red litmus paper and blue litmus paper. The table shows the colour changes it can make.

	Red Litmus	Blue Litmus
Acidic solution	Stays red	Turns red
Neutral solution	Stays red	Stays blue
Alkaline solution	Turns blue	Stays blue

Notice how we say 'stays red'. This is better than saying 'nothing' or 'stayed the same', because it tells us the colour we actually see.

blue litmus paper turning red when dipped into acid

Acids turn blue litmus paper red

red litmus paper turning blue when dipped into alkali solution

Alkalis turn red litmus paper blue

Universal indicator and the pH scale

Universal indicator is a mixture of several different indicators. Unlike litmus, universal indicator can show us exactly how strongly acidic or alkaline a solution is. This is measured using the pH scale. The pH scale runs from pH 0 to pH 14.
Universal indicator has many different colour changes, from red for strong acids to dark purple for strong bases. In the middle, neutral pH 7 is indicated by green.

Photograph of different pH levels, randing from red to violet.

Universal indicator shows how acidic or alkaline a solution is

These are the important points about the pH scale:

neutral solutions are pH 7 exactly
acidic solutions have pH values less than 7
alkaline solutions have pH values more than 7
the closer to pH 0 you go, the more strongly acidic a solution is
the closer to pH 14 you go, the more strongly alkaline a solution is

Reactions of acids with bases

A chemical reaction happens if you mix together an acid and a base. The reaction is called neutralisation, and a neutral solution is made if you add just the right amount of acid and base together.

Metal oxides and metal hydroxides

Metal oxides and metal hydroxides are two types of bases. For example copper oxide and sodium hydroxide.
Here are general word equations for what happens in their neutralisation reactions with acids.
metal oxide + acid → a salt + water
metal hydroxide + acid → a salt + water
Notice that a salt and water are always produced. The mixture usually warms up a little during the reaction, too. The exact salt made depends upon which acid and base were used.

Carbonates and hydrogen carbonates

Carbonates and hydrogen carbonates are two other types of base. They also make a salt and water when we neutralise them with acid. But this time we get carbon dioxide gas too.
The reaction fizzes as bubbles of carbon dioxide are given off. This is easy to remember because we see the word 'carbonate' in the chemical names.
These are the general word equations for what happens:
acid + metal carbonate → a salt + water + carbon dioxide
acid + metal hydrogen carbonate → a salt + water + carbon dioxide

Using neutralisation

Farmers use lime (calcium oxide) to neutralise acid soils.
Your stomach contains hydrochloric acid, and too much of this causes indigestion. Antacid tablets contain bases such as magnesium hydroxide and magnesium carbonate to neutralise the extra acid.
Bee stings are acidic. They can be neutralised using baking powder, which contains sodium hydrogen carbonate.

Naming salts

A salt is always made when an acid is neutralised by a base. But the exact salt made depends upon which acid and base were used.
The name of a salt has two parts:

the first part comes from the metal in the base used
the second part comes from the acid that was used

Example

Where does the name potassium nitrate come from?

The potassium comes from a base containing potassium such as potassium hydroxide. The nitrate comes from nitric acid.

These are the rules for the second part of the name of a salt:

Acid used	Second part of salt's name
hydrochloric acid	chloride
sulphuric acid	sulphate
nitric acid	nitrate

Example: copper sulphate

Copper sulfate crystal

How can we make copper sulphate? The first part of the name is 'copper', so we need a base containing copper. We could use copper oxide or copper carbonate, for example. The second part of the name is 'sulphate', so we need to use sulphuric acid.
Here are word equations for those reactions.
copper oxide + sulphuric acid → copper sulphate + water
copper carbonate + sulphuric acid → copper sulphate + water + carbon dioxide

Example: sodium chloride

How can we make sodium chloride? The first part of the name is 'sodium', so we need a base containing sodium. We could use sodium hydroxide or sodium hydrogen carbonate, for example. The second part of the name is 'chloride', so we need to use hydrochloric acid.
Here are word equations for those reactions.
sodium hydroxide + hydrochloric acid → sodium chloride + water
sodium hydrogen carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide
It would be very difficult to neutralise the acid in these reactions perfectly exactly. Some acid or base would be left over. So it would not be safe to taste the sodium chloride solution produced.

Reactions of acids with metals

Acids react with most metals and a salt is produced. But unlike the reaction between acids and bases we don't get any water. Instead we get hydrogen gas.
This is the general word equation for the reaction:
metal + acid → salt + hydrogen

Salts

The salt produced depends upon the metal and the acid. Here are two examples:
zinc + sulphuric acid → zinc sulphate + hydrogen
magnesium + hydrochloric acid → magnesium chloride + hydrogen
It doesn't matter which metal or acid is used, if there is a reaction we always get hydrogen gas as well as the salt.

The test for hydrogen

There is a simple laboratory test to see if a gas is hydrogen. A lighted wooden splint goes pop if it is put into a test tube of hydrogen. This is because the flame ignites the hydrogen, which burns explosively to make a loud sound.

Acids and hydrogen

All acids contain hydrogen atoms. Apart from hydrochloric acid, this is not clear from their names, but you can tell they contain hydrogen from their chemical formulae. Remember that the chemical symbol for hydrogen is H.

Name of acid	Chemical formula of acid
hydrochloric acid	HCl
nitric acid	HNO₃
sulphuric acid	H₂SO₄
carbonic acid	H₂CO₃
phosphoric acid	H₃PO₄

Sources of Heat (Laboratory Manual)

By : James W Zubrick
Email: j.zubrick@hvcc.edu
Many times you’ll have to heat something. Don’t just reach for the Bunsen burner. That flame you start just may be your own. There are alternate sources you should think of first.

THE STEAM BATH

If one of the components boils below 70 °C and you use a Bunsen burner, you may have a hard time putting out the fire. Use a steam bath!
1. Find a steam tap. It’s like a water tap, only this one dispenses steam (Caution! You can get burned.)
2. Connect tubing to the tap now. It’s going to get awfully hot in use. Make sure you’ve connected a piece that’ll be long enough to reach your steam bath.
3. Don’t connect this tube to the steam bath yet! Just put it into a sink. Because steam lines are usually full of water from condensed steam, drain the lines first, otherwise you’ll waterlog your steam bath.
4. Caution! Slowly open the steam tap. You’ll probably hear bonking and clanging as steam enters the line. Water will come out. It’ll get hotter and may start to spit.
5. Wait until the line is mostly clear of water, then turn off the steam tap. Wait for the tubing to cool.
6. Slowly, carefully, and cautiously, making sure the tube is not hot, connect the tube to the inlet of the steam bath. This is the uppermost connection on the steam bath.

7. Connect another tube to the outlet of the steam bath—the lower connection—and to a drain. Any water that condenses in the bath while you’re using it will drain out.
Usually, steam baths have concentric rings as covers. You can control the “size” of the bath by removing various rings.
Never do this after you’ve started the steam. You will get burned!
And don’t forget—round-bottom flasks should be about halfway in the bath. Whether you should let steam rise up all around the flask or not appears to be a matter of debate. Lots of steam will certainly steam up the lab and may expose you to corrosion inhibitors (morpholine) in the steam lines. You should not, however, have steam shooting out the sides of the bath, or any other place. (Fig. 57).

THE BUNSEN BURNER

The first time you get the urge to take out a Bunsen burner and light it up, don’t. You may blow yourself up. Please check with your instructor to see if you even need a burner. Once you find out that you can use a burner, assume that the person who used it last didn’t know much about burners, and take some precautions so as not to burn your eyebrows off.
Now Bunsen burners are not the only kind. There are Tirrill burners and Meker burners as well. Some are more fancy than others, but they work pretty much the same. So when I say burner anywhere in the text it could be any of them.

Fig. 57 The steam bath in use.
1. Find the needle valve. This is at the base of the burner. Turn it fully clockwise (inward) to stop the flow of gas completely. If your burner doesn’t have a needle valve, it’s a traditional Bunsen burner and the gas flow has to be regulated at the bench stopcock (Fig. 58). This can be dangerous, especially if you have to reach over your apparatus and burner to turn off the gas. Try to get a different model.
2. There is a moveable collar at the base of the burner which controls air flow. For now, see that all the holes are closed (i.e., no air gets in).
3. Connect the burner to the bench stopcock by some tubing and turn the bench valve full on. The bench valve handle should be parallel to the outlet (Fig. 58).
4. Now, slowly open the needle valve. You may be just able to hear some gas escaping. Light the burner. Mind your face! Don’t look down at the burner as you open the valve.
5. You’ll get a wavy yellow flame, something you don’t really want. But at least it’ll light. Now open the air collar a little. The yellow disappears; a blue flame forms. This is what you want.

Fig. 58 More than you may care to know about burners.
6. Now, adjust the needle valve and collar (the adjustments play off each other) for a steady blue flame.

Burner Hints

1. Air does not burn. You must wait until the gas has pushed the air out of the connecting tubing. Otherwise, you might conclude that none of the burners in the lab work. Patience, please.
2. When you set up the distillation or reflux, don’t waste a lot of time raising and lowering the entire setup so the burner will fit. This is nonsense. Move the burner! Tilt it! (See Fig. 59). If you leave the burner motionless under the flask, you may scorch the compound and your precious product can become a “dark intractable material.”

Fig. 59 Don’t raise the flask, lower the burner.
3. Placing a wire gauze between the flame and the flask spreads out the heat evenly. Even so, the burner may have to be moved around. Hot spots can cause star cracks to appear in the flask (see Chapter 4, “Round-Bottom Flasks”).
4. Never place the flask in the ring without a screen (Fig. 60). The iron ring heats up faster than the flask and the flask cracks in the nicest line around it you’ve ever seen. The bottom falls off and the material is all over your shoes.

THE HEATING MANTLE

A very nice source of heat, the heating mantle takes some special equipment and finesse.
1. Variable voltage transformer. The transformer takes the quite lethal 120 V from the wall socket and can change it to an equally dangerous 0 to 120 V, depending on the setting on the dial. Unlike temperature settings on a Mel-Temp, on a transformer 0 means 0 V, 20 means 20 V, and so on. I like to start at 0 V and work my way up. Depending on how much heat you want, values from 40 to 70 seem to be good places to start.

Fig. 60 Flask in the iron ring.
Also, you’ll need a cord that can plug into both the transformer and the heating mantle.
2. The traditional fiberglass heating mantle. An electric heater wrapped in fiberglass insulation and cloth that looks vaguely like a catcher’s mitt (Fig. 61).
3. The Thermowell heating mantle. You can think of the Thermowell heating mantle as the fiberglass heating mantle in a can. In addition, there is a hard ceramic shell that your flask fits into (Fig. 62). Besides just being more mechanically sound, it’ll help stop corrosive liquids from damaging the heating element if your flask cracks while you’re heating it.
4. Things not to do

a. Don’t ever plug the mantle directly onto the wall socket! I know, the curved prongs on the mantle connection won’t fit, but the straight prongs on the adapter cord will. Always use a variable voltage transformer and start with the transformer set to zero.
b. Don’t use too small a mantle. The only cure for this is to get one that fits properly. The poor contact between the mantle and the glass doesn’t transfer heat readily and the mantle burns out.
c. Don’t use too large a mantle. The only good cure for this is to get one that fits properly. An acceptable fix is to fill the mantle with sand, after the flask is in, but before you turn the voltage on. Otherwise, the mantle will burn out.
HINT. When you set up a heating mantle to heat any flask, usually for distillation or reflux, put the mantle on an iron ring and keep it clamped a few inches above the desktop (Fig. 61). Then clamp the flask at the neck, in case you have to remove the heat quickly. You can just unscrew the lower clamp and drop the mantle and iron ring.

PROPORTIONAL HEATERS AND STEPLESS CONTROLLERS

In all these cases of heating liquids for distillation or reflux, we really control the electric power, not the heat or temperature directly. Power is applied to the heating elements, they warm up, yet the final temperature is determined by the heat loss to the room, the air, and, most important, the flask you’re heating. There are several types of electric power controls

Fig. 61 Round-bottom flask and mantle ready to go.
1. The variable voltage transformer. We’ve discussed this just previously. Let me briefly restate the case: Set the transformer to 50 on the 0 -100 dial and you get 50% of the line voltage, all the time, night and day, rain or shine.
2. The mechanical stepless controller. This appears to be the inexpensive replacement for the variable voltage transformer. Inside one model there’s a small heating wire wound around a bimetal strip with a magnet at one end (Fig. 63). A plunger connected to the dial on the front panel changes the distance between the magnet and a metal plate. With a heating mantle attached, when you turn the device on, current goes through the small heating wire and the mantle. The mantle is now on full blast (120V out of 120V from the electric wall socket)! As the small heating wire warms the bimetal strip, the strip expands, distorts, and finally pulls the magnet from its metal plate, opening the circuit. The mantle now cools rapidly (0V out of 120V from the wall socket), along with the bimetal strip. Eventually, the strip cools enough to let the magnet get close to that metal plate, and—CLICK—everything’s on full tilt again.

Fig. 62 A Thermowell heating mantle.

Fig. 63 Inside a mechanical stepless controller.
The front panel control varies the duty cycle, the time the controller is full on, to the time the controller is full off. If the flask, contents, and heating mantle are substantial, it takes a long time for them to warm up and cool down. A setup like that would have a large thermal lag. With small setups (approx. 50 ml. or so), there is a small thermal lag and very wild temperature fluctuations can occur. Also, operating a heating mantle this way is just like repeatedly plugging and unplugging it directly into the wall socket. There are not many devices that easily take that kind of treatment.
3. The electronic stepless controller. Would you believe a light dimmer? The electronic controller has a triac, a semiconductor device, that lets fractions of the a.c. power cycle through to the heating mantle. The a.c. power varies like a sine wave, from 0 to 120V from one peak to the next. At a setting of 25%, the triac remains off during much of the a.c. cycle, finally turning on when the time is right (Fig. 64). Although the triac does turn “full-off and full-on,” it does so at times so carefully controlled, that the mantle never sees full line power (unless you deliberately set it there).

Fig. 64 Light dimmer and heating mantle triac power control.
Laboratory Resource Packet 2014/2015

TO THE STUDENT
Chemistry is exciting! Each day in the laboratory you are given the opportunity to confront the unknown, and to understand it. Each experiment holds many secrets. Look hard and you may see them. Work hard and you can solve them. The word science comes from the Latin word scire, which means “to know.” The goal of all science is knowledge. Scientists are men and women who devote their lives to the pursuit of knowledge.
In this class, you are given the opportunity to do what scientists do. You can wonder how things work, ask why and how, and then think of ways to answer your own questions. You are given the chance to understand what is unknown to you and to many other people. It is a great opportunity. Do not waste it by being lazy or careless. Work hard. Master the scientist’s skills of observation and experiment. These skills are tools to solve the secrets of the unknown.

SAFETY
Chemistry is a laboratory science. As part of your laboratory experience you will handle many chemical substances and manipulate specialized laboratory equipment. Many of these substances pose a health risk if handled improperly, while some of the laboratory equipment can cause severe injury if used improperly. This section is a guide to the safe laboratory practices you will use throughout this course.

Preparation and Safety
To get the most out of your laboratory experience, you must be well prepared for each experiment. This means that you must read the experiment thoroughly before coming to the laboratory. Make sure you have a clear idea of what the experiment is about. Be sure that you understand each step of the procedure. If you are unsure of any part of the experiment, ask your teacher for help before the laboratory begins.
Preparation is important not only to understanding, but also to safety. If you are well prepared for the laboratory, it is much less likely that an accident will occur. In the laboratory, you are responsible not only for your safety, but also for the safety of your classmates. If an accident happens because you are not prepared, it can also affect your friends. This is all the more reason for you to take the time and make the effort to prepare for the laboratory.
Be sure to note the safety warnings listed in the Safety section of each experiment. Note that these warnings are emphasized by symbols appearing in the margins. The symbols mark those parts of the procedure that may be hazardous. In addition, be sure to observe the general safety precautions described in the safety section at the beginning of the manual. Finally, remember the most important safety advice of all: Always wear safety goggles in the chemistry laboratory!

Laboratory Hazards
You should be aware of possible hazards in the laboratory and take the appropriate safety precautions. By doing so, you can minimize the risks of doing chemistry. This safety section is intended to acquaint you with the hazards that exist in the laboratory and to indicate how you can avoid these hazards. In addition, information is provided on what to do if an accident should occur.

Thermal Burns
A thermal burn can occur if you touch hot equipment or come too close to an open flame. You can prevent thermal burns by being aware that hot and cold equipment look the same. If a gas burner or hot plate has been used, some of the equipment nearby may be hot. Hold your hand near an item to feel for heat before touching it.
Treat a thermal burn by immediately running cold water over the burned area. Continue applying the cold water until the pain is reduced. This usually takes several minutes. In addition to reducing pain, cooling the burned area also serves to speed the healing process. Greases and oils should not be used to treat burns because they tend to trap heat. Medical assistance should be sought for any serious burn. Notify your teacher immediately if you are burned.

Chemical Burns
A chemical burn occurs when the skin or a mucous membrane is damaged by contact with a substance. The Materials section of each exercise indicates which substances can cause chemical burns. c stands for corrosive. It indicates that the chemical can cause severe burns. I stands for irritant. It indicates that the chemical can irritate the skin and the membranes of the eye, nose, throat, and lungs. Chemicals that are marked corrosive should be treated with special care. Chemical burns can be severe. Permanent damage to mucous membranes can occur despite the best efforts to rinse a chemical from the affected area.
The best defense against chemical burns is prevention. Without exception, wear safety goggles during all phases of the laboratory period— even during cleanup. Should any chemical splash in your eye, immediately use a continuous flow of running water to flush your eye for a period of 20 minutes. Call for help. If you wear contact lenses, remove them immediately. This is especially crucial if the chemical involved is an acid or base. It can concentrate under the lens and cause extensive damage. Wear a laboratory apron and close-toed shoes (no sandals) to protect other areas of your body. If corrosive chemicals should contact your exposed skin, wash the affected area with water for several minutes.
An additional burn hazard exists when concentrated acids or bases are mixed with water. The heat released in mixing these chemicals with water can cause the mixture to boil, spattering corrosive chemical. The heat can also cause non-Pyrex containers to break, spilling corrosive chemical.
To avoid these hazards, follow these instructions: Always add acid or base to water, very slowly while stirring; never the reverse. One way to remember this critical advice is to think of the phrase “Pouring acid into water is doing what you ought-er.”
Estimates for the time required for permanent corneal damage to occur following exposure to 1M NaOH are in the range of 30 seconds. Concentrated sulfuric acid causes thermal burns because it reacts with water in the skin, releasing substantial amounts of heat. Nitric acid does not produce thermal burns, but reacts with the proteins in the skin, destroying tissue. Nitric acid burns are very slow to heal.

Cuts from Glass
Cuts occur most often when thermometers or pieces of glass tubing are forced into rubber stoppers. Prevent cuts by using the correct technique for this procedure. The hole should be lubricated with glycerol or water to facilitate the movement of the glass tubing. The glass should not be gripped directly with the hands, but rather by means of cloth towels. The towels will protect your hands if the glass should break. Use a gentle twisting motion to move the tube smoothly into the stopper. Avoid cuts from other sources by discarding chipped and cracked glassware according to your teacher’s instructions. If you should receive a minor cut, allow it to bleed for a short time. Wash the injured area under cold running water, and notify your teacher. Serious cuts and deep puncture wounds require immediate medical help. Notify your teacher immediately. While waiting for assistance, control the bleeding by applying pressure with the fingertips or by firmly pressing with a clean towel or sterile gauze.

Fire
A fire may occur if chemicals are mixed improperly or if flammable materials come too close to a burner flame or hot plate. When using lab equipment, prevent fires by tying back long hair and loose-fitting clothing. Do not use a burner when flammable chemicals are present. Flammable chemicals are designated with the symbol f in the Materials section for each exercise. Use a hot plate as a heat source instead of a burner when flammable chemicals are present. If hair or clothing should catch fire, do not run, because running fans a fire. Drop to the floor and roll slowly to smother the flames. Shout for help. If another person is the victim, get a fire blanket to smother the flames. If a shower is nearby, help the victim to use it. In case of a fire on a laboratory bench, turn off all accessible gas outlets and unplug all accessible appliances. A fire in a container may be put out by covering the container with a nonflammable object. It could also be smothered by covering the burning object with a damp cloth. If not, call for a fire extinguisher. Spray the base of the fire with foam from the extinguisher. CAUTION: Never direct the jet of a fire extinguisher into a person’s face. Use a fire blanket instead. If a fire is not extinguished quickly, leave the laboratory. Crawl to the door if necessary to avoid the
smoke. Do not return to the laboratory.

Poisoning
Many of the chemicals used in this manual are toxic. Toxic chemicals are identified in the Materials sections with the symbol T. You should do several things to prevent poisoning. Never eat, chew gum, or drink in the laboratory. Do not touch chemicals. Clean up spills.
Keep your hands away from your face. In this way you will prevent chemicals from reaching your hands, mouth, nose, or eyes. In some cases, the detection of an odor is used to indicate that a chemical reaction has taken place. It is important to note, however, that many gases are toxic when inhaled. If you must detect an odor, use your hand to waft some of the gas toward your nose. Sniff the gas instead of taking a deep breath. This will minimize the amount of gas sampled. Glycerol should not be used in the presence of powerful oxidizers such as sulfuric acid, nitric acid, dichromates, or permanganates.
Carbon dioxide fire extinguishers have the advantage of being very effective in fires involving flammable liquids or electricity. However, carbon dioxide extinguishers are not useful in fires involving wood or embers. Carbon dioxide does have the advantage of not leaving any residue should discharge occur. ABC fire extinguishers discharge a powder which is effective on all fires except those that involve metals. ABC extinguishers do leave a residue, which must be removed. Aim the discharge at the base of the fire. Post the telephone number of your local Poison Control Center in the classroom, or have the number readily available.

LABORATORY TECHNIQUES
Working in the chemistry laboratory, you will be handling potentially dangerous substances and performing unfamiliar tasks. This section provides you with a guide to the safe laboratory techniques needed in
this course. While performing experiments throughout the year, refer back to this section any time you are unsure of proper laboratory techniques.

• Always read the label on a reagent bottle before using its contents.
• Always wear safety goggles when handling chemicals.
• Never touch chemicals with your hands.
• Never return unused chemicals to their original containers. To avoid waste, do not take excessive amounts of reagents.

Pouring liquids
1. Use the back of your fingers to remove the stopper from a reagent bottle. Hold the stopper between your fingers until the transfer of liquid is complete. Do not place the stopper on your workbench.
2. Grasp the container from which you are pouring with the palm of your hand covering the label.
3a. When you are transferring a liquid to a test tube or measuring cylinder, the container should be held at eye level. Pour the liquid slowly, until the correct volume has been transferred.
3b. When you are pouring a liquid from a reagent bottle into a beaker, the reagent should be poured slowly down a glass stirring rod. When you are transferring a liquid from one beaker to another, you can hold the stirring rod and beaker in one hand.

Filtering a Mixture
Sometimes it is necessary to separate a solid from a liquid. The most common method of separating such a mixture is filtration.
1. Fold a filter paper circle in half and then quarters. Open the folded paper to form a cone, with one thickness of paper on one side and three thicknesses on the other.
2. Put the paper cone in a filter funnel. Place the funnel in an iron ring clamped to a ring stand. Moisten the filter paper with a small volume of distilled water, and gently press the paper against the sides of the funnel to achieve a good fit. (If the correct size of filter paper has been used, the top edge of the cone will be just below the rim of the filter funnel.)
3. Place a beaker beneath the funnel to collect the filtrate. The tip of the funnel should touch the inside surface of the beaker and extend about one inch below the rim. Guide flow of liquid with a glass rod Mixture being filtered Filtrate Solid collects on filter paper Stem touches side of beaker.
4. Decant the liquid from the solid by pouring it down a glass stirring rod into the funnel. Be careful to keep the liquid below the top edge of the cone of filter paper at all times; the liquid must not overflow. Finally, use a jet of distilled water from a wash bottle to wash the solid into the filter.
5. When the filtration is complete, wash the solid residue on the filter paper with distilled water to remove traces of solvent. Dry the solid.
6. If the filtrate contains a dissolved salt, it may be recovered by evaporation if desired.
Using a Gas Burner
Laboratory gas burners produce various kinds of flames when different mixtures of gas and air are burned. The two most common models are the Bunsen burner and the Tirrell burner. Both have adjustable air vents;
the Tirrell burner has a gas control valve in its base.
1. Examine your laboratory burner. Determine which model you have.
2. Connect the burner to the gas supply with rubber tubing.
3. Close the air vents. If your model is a Tirrell burner, also close the gas control valve at the base of the burner.
4. Hold a lighted match at the top of the burner tube and turn on the gas supply. Do this by opening the main gas supply valve located on top of the nozzle to which you attached the rubber tubing. (If your model is a Tirrell burner, first open the main gas supply valve, then open the gas control valve at the base approximately onehalf- turn.) You should get a yellow, or luminous, flame. When a Tirrell burner is used, the main gas supply valve should be opened fully and the gas flow regulated by the gas control valve. Gas supply to a Bunsen burner is controlled by the main gas valve.
5. Open the air vents slowly, to admit more air into the flame, to produce a light blue (nonluminous) cone-shaped flame. If the flame “blows out” after lighting, the gas supply should be reduced.
6. Adjust the air vents and gas supply to produce the desired size of flame. For most laboratory work, the blue inner cone of the flame should be about 1 inch high and free of yellow color. If you want a smaller flame, close the air vent slightly and reduce the gas supply. You will learn how to control the burner flame by trial and error.
7. Turn the burner off at the main gas supply valve when done. CAUTION: Confine long hair and loose clothing when using a gas burner. Do not reach over a burner. Ensure that flammables are not being used when a burner is lit. Never leave a lit burner unattended. Know the location of fire extinguishers, the fire blanket, and safety
shower.
Heating Liquids
Heating a Liquid in a Test Tube
The correct procedure for heating liquids in the laboratory is important to laboratory safety.
1. Adjust your gas burner to produce a gentle blue flame.
2. Fill a test tube one-third full with the liquid to be heated.
3. Grasp the test tube with a test-tube holder, near the upper end of the tube.
4. Hold the test tube in a slanting position in the flame, and gently heat the tube a short distance below the surface of the liquid.
5. Shake the tube gently as it is being heated, until the liquid boils or reaches the desired temperature.
CAUTION: Never point the open end of a test tube you are heating either toward yourself or anyone working nearby. Never heat the bottom of the test tube.
Heating a Liquid in a Beaker
Many laboratory experiments require the use of a hot water or boiling water bath. This procedure describes how to assemble a water bath.
1. Fasten an iron ring securely to a ring stand so that it is 2–4 cm above the top of a gas burner placed on the ring stand base.
2. Place a 250-mL beaker one-half-filled with water on a wire gauze resting on the iron ring.
3. Light your gas burner and adjust it to produce a hot flame.
4. Place the burner beneath the wire gauze. For a slower rate of heating, reduce the intensity of the burner flame.
CAUTION: Never heat plastic beakers or graduated glassware in a burner flame. Never let a boiling water bath boil dry; add water to it as necessary.

Inserting Glass Tubing
In many experimental procedures, you are required to insert a thermometer or a length of glass tubing into a hole in a rubber stopper. It is essential that you know the correct way to do this. Otherwise, serious injury may result.
1. Lubricate the end of the glass tubing with a few drops of water, washing-up liquid, glycerol, or vegetable oil.
2. Hold the glass tubing close to where it enters the hole in the rubber stopper. Protect your hands with work gloves or pieces of cloth.
3. Ease the tubing into the hole with a gentle twisting motion. Push the tubing through the hole as far as is required. Do not use force!
4. Wipe excess lubricating material from the tubing before continuing with the experiment.
5. If the glass tubing is to be removed from the stopper, it should be done immediately after the experiment is completed.
CAUTION: The end of the glass tubing should be fire-polished or smoothed with emery cloth before being inserted into a rubber stopper. Do not try to bend the glass tubing—it will break. Ensure that the palm of the hand holding the rubber stopper is not in line with the emerging glass tube.

Measuring Mass
In many experiments you are required to determine the mass of a chemical used or produced in a reaction. An object’s mass is determined by measuring it on a balance. When you determine the mass of an object, you are comparing its mass with a known mass. In the SI, the base unit of mass is the kilogram.

• Check the balance before you start. The balance pan should be empty and clean, and all masses (or dials) should be set on zero. The balance must be level. Check the bubble level on the base. See your
teacher if you need assistance with checking your balance.
• Objects to be placed directly on the balance pan must be clean, dry, and at room temperature. Solid chemicals and liquids must never be put directly on the balance pan. Liquid samples should be placed in beakers or sealed containers. Solid chemicals can be conveniently placed in beakers, disposable plastic weighing boats, or on 10-cm squares made of glossy paper.
• The balance is a precision instrument that must be handled with care. To avoid damaging it, always be sure that the balance is in an arrested position when objects are placed on or removed from the pan. Always turn all dials slowly.
• Never move or jar either a balance or the balance table.
• If you spill a chemical on or near the balance, clean it up immediately. If in doubt, inform your teacher. A camel-hair brush is usually provided to wipe minute traces of solid from the balance pan before you use it.
• Never attempt to measure an object with a mass greater than the maximum capacity of the balance.
• When you are done, return all the masses to zero, and make sure the balance pan is clean.
Do not attempt to use a balance until your teacher has demonstrated the proper technique.

Measuring Volume
Volume measurements are important in many experimental procedures. Sometimes volume measurements must be accurate; other times they can be approximate. Most volume measures in the laboratory are made using equipment calibrated in milliliters. Although some beakers have graduation marks, these marks are designed only for quick, rough estimates of volume. Accurate volumes must be measured with pipets, burets, or volumetric flasks.
Using a Graduated Cylinder
Half-fill a 100-mL graduated cylinder with water, and set the cylinder on your laboratory bench. Examine the surface of the water. Notice how the surface curves upward where the water contacts the cylinder walls. This
curved surface is called a meniscus.
A volume measurement is always read at the bottom of the meniscus, with your eye at the same level as the liquid surface. To make the meniscus more visible, you can place your finger or a dark piece of paper behind and just below the meniscus while making the reading.
Graduated cylinders are available in many capacities. The 100-mL cylinder is marked in 1-mL divisions, and volumes can be estimated to the nearest 0.1 mL. The last digit in these measurements is therefore significant
but uncertain.
Using a Pipet
A pipet is used to accurately measure and deliver volumes of liquids. Two types are in common use: volumetric pipets and graduated, or measuring, pipets. The use of a volumetric pipet will be described. A volumetric pipet has a single calibration mark and delivers the volume printed on the bulb of the pipet at the temperature specified. (A graduated pipet has calibrations along the length of the pipet.) Volumes can be measured more accurately with a volumetric pipet than with a graduated pipet.
1. Place the tip of the pipet below the surface of the liquid to be dispensed.
2. Compress a pipet bulb and press the hole in the bulb against the upper end of the pipet. CAUTION: Never fill a pipet by applying suction with your mouth. Never push the pipet bulb over the end of the pipet.
3. Slowly release pressure on the bulb so that liquid is drawn into the pipet to a level about 2 cm above the calibration mark.
4. Remove the bulb and simultaneously place your index finger over the end of the pipet. If you are right-handed, you should hold the pipet in your right hand and the pipet bulb in your left.
5. Keep your index finger pressed firmly against the end. Withdraw the pipet from the liquid, and carefully wipe the outside of the stem with a paper towel.
6. Slowly reduce the pressure on your finger to allow the excess liquid to drain into a waste receiver, until the bottom of the meniscus is at the calibration mark.
7. Now, deliver the remaining liquid in the pipet into the designated receiver. When releasing liquid from a volumetric pipet, let it drain completely. Wait 20 seconds, then touch the pipet tip to the side of the flask or surface of the liquid. This action will remove some, but not all, of the liquid in the tip. The pipet delivers the stated volume when this procedure is followed. A small amount of liquid remains in the tip. Do not blow this out into your receiver.
Glassworking
Cutting and Fire Polishing
1. Place the glass tubing or glass rod on a flat surface (such as the laboratory bench).
2. Hold the glass tightly with one hand close to the area to be cut.
3. Using a firm stroke, make a single deep scratch with a triangular file.
CAUTION: Do not use a sawing motion or repeated scratching.
4. Grasp the glass in both hands with the scratch facing away from you and both thumbs directly behind the scratch.
5. Push firmly with the thumbs and pull with your fingers. The glass should snap with a clean break.
CAUTION: Be careful with the cut ends of the glass. They may be sharp and jagged. Do not attempt to break glass tubing having an outside diameter greater than 6 mm.
6. The cut ends of the glass tubing should be fire-polished to make the tubing safe to handle. Rotate one end of the glass tube in the hottest part of a burner flame, until the sharp edges have softened and become rounded.
CAUTION: Do not hold the tubing in the flame too long. If you do, the hole in the tube will close.
7. Place the hot glass on a wire gauze square to cool.
CAUTION: Hot glass and cold glass look alike. Make sure one end of a piece of glass has cooled before you attempt to fire-polish the other end.
Bending Glass Tubing
1. Put a wing top or flame spreader on your gas burner.
2. Light the burner and adjust the flame to produce an even blue (hot) flame across the wing top.
3. Grasp a length of glass tubing that has been fire-polished at both ends. Hold the center of it lengthwise in the flame, just at the top of the blue region. This is the hottest part of the flame.
4. Rotate the tubing in the flame to heat approximately a 5-cm section uniformly, until it becomes soft and just begins to sag.
5. Remove the tubing from the flame and bend it to the desired shape in one movement.
6. When it has hardened, put the glass tubing on a wire gauze to cool.
CAUTION: Hot and cold glass look alike.

The particle model - Test

In which two states are the particles randomly arranged?

liquid and solid

liquid and gas

gas and solid

In which state are the particles only able to vibrate in a fixed position?

solid

liquid

gas

Which state can be compressed or squashed easily?

solid

liquid

gas

Which state is shown in this diagram?

http://www.bbc.co.uk/bitesize/ks3/science/testbiteimages/sci_dia_02.jpg

liquid

solid

gas

Which state cannot flow from place to place?

solid

liquid

gas

Particles in which state have no bonds?

liquid

solid

gas

Particles in which state sit in a regular pattern and are held together tightly by bonds?

solid

liquid

gas

Behaviour of matter - Test

What happens to the particles when a piece of rock is heated up?

they get bigger

they get smaller

they stay the same size

What happens to a bar of steel when it is cooled down?

it gets longer

it gets shorter

it stays the same length

What happens to the pressure in a metal spray can when it is heated up?

it increases

it decreases

it stays the same

Why do gases exert a pressure on the walls of their container?

the gas particles hit each other

the gas particles move quickly in all directions

the gas particles hit the container walls

What process causes smelly gases to spread around a room on their own?

refusion

diffusion

diffraction

Atoms and elements - Test

Which of these is the smallest particle?

an atom

a molecule

a speck of dust

Which of these is the correct symbol for magnesium?

Which statement about elements is correct?

most elements are metals

most elements are non-metals

there are about the same number of metals and non-metals

Where are the metals found in the periodic table?

on the left

on the right

scattered all over

Which of the following is not a general property of metals?

shiny

good conductor of heat

poor conductor of electricity

Which of the following is not a general property of non-metals?

brittle

strong

poor conductor of heat

An element sinks in water and makes ringing sound when hit. It is most likely to be:

a metal

a non-metal

an alloy

Compounds and mixtures - Test

How many different atoms are there in a compound?

one

always two

two or more

Does this show an element, a mixture or a compound?
small circles are joined in pairs

compound

mixture

element

Which statement about atoms and molecules is correct?

elements always exist as separate atoms.

elements always exist as pairs of atoms called molecules.

elements and compounds can exist as molecules.

Is water an element, compound or mixture?

element

compound

mixture

Which is the best way to get salt from salty water?

evaporation

filtration

distillation

Pure water can be separated from inky water by simple distillation. This is because:

water and ink have different boiling points.

water evaporates leaving the ink particles behind.

ink evaporates leaving the water behind.

What is the correct order for obtaining salt from a mixture of sand and salt?

dissolving in water - filtration - evaporation

evaporation - filtration - dissolving in water

filtration - dissolving in water - evaporation

Which method is usually used to separate coloured substances from each other?

simple distillation

evaporation

chromatography

Which of these three metals is the most reactive: potassium, iron or gold?

potassium

iron

gold

10.

Which of these three metals is the least reactive: iron, copper or platinum?

iron

copper

platinum

11.

Copper and oxygen react to form which compound?

copper oxygen

copper oxide

carbon dioxide

Acids and bases and metals - Test

What does this hazard symbol mean?
shows two test tubes dripping liquid onto two objects. Where the liquid has come into contact with the object, the object has been corroded

shows two test tubes dripping liquid onto two objects. Where the liquid has come into contact with the object, the object has been corroded

corrosive

irritant

harmful

Which of these acids is most likely to be dangerous?

citric acid

carbonic acid

hydrochloric acid

Which statement about bases is true?

they are all alkalis

they can neutralise acids

they are all soluble

Which statement about alkalis is true?

they are all bases

they cannot neutralise acids

they are all insoluble

What happens to litmus paper in acidic solutions?

red litmus turns blue

blue litmus turns red

yellow litmus turns green

Universal indicator solution is usually green to begin with. What does this mean?

it is acidic

it is alkaline

it is neutral

A liquid has a pH of 7.5 - what does this mean?

it is weakly acidic

it is weakly alkaline

it is neutral

A liquid has a pH of 1 - what does this mean?

it must be sodium hydroxide solution

it is strongly acidic

it is weakly acidic

What products are formed when a metal oxide reacts with an acid?

a salt only

a salt and water

a salt, water and carbon dioxide

10.

What products are formed when a metal carbonate reacts with an acid?

a salt only

a salt and water

a salt, water and carbon dioxide

11.

Farmers use lime to neutralise their soils. What sort of substance is lime?

a base

an acid

a sharp tasting drink

12.

Which acid could be used to make ammonium nitrate (a type of fertiliser)?

hydrochloric acid

sulfuric acid

nitric acid

13.

Which salt is made when copper oxide and sulfuric acid react together?

copper sulfate

copper sulfuroxide

copper sulfide

14.

Which gas is produced when magnesium reacts with hydrochloric acid?

carbon dioxide

oxygen

hydrogen

Saturday, 23 August 2014

CHEMISTRY READINGS

ABOUT CHEMISTRY

Contents

Etymology

Definition

History

Chemistry as science

Chemical structure

Principles of modern chemistry

Matter

Atom

Element

Compound

Molecule

Substance and mixture

Mole and amount of substance

Phase

Bonding

Energy

Reaction

Ions and salts

Acidity and basicity

Redox

Equilibrium

Chemical laws

Practice

Subdisciplines

Chemical industry

Scientific Method Steps

Learn the Steps of the Scientific Method

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6 Steps of the Scientific Method

Scientific Method Steps

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What Are Examples of a Hypothesis?

Ads

Examples of the Null Hypothesis

Examples of an If, Then Hypothesis

Improving a Hypothesis To Make It Testable

Elements of a Good Hypothesis

What Makes a Good Experimental Hypothesis?

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Mixtures

Mixture and compounds

An example - iron, sulphur and iron sulphide

Separating mixtures

Chromatography

Separating dissolved substances

Separating dissolved substances

Separating dissolved substances

Filtration

Separating insoluble solids

Separating insoluble solids

Separating insoluble solids

Evaporation

Separating a soluble solid

Separating a soluble solid

Separating a soluble solid

Simple distillation

Separating a liquid from a solution

Separating a liquid from a solution

Separating a liquid from a solution

Fractional distillation

Separating two or more liquids

Separating two or more liquids

Separating two or more liquids

Compounds

Properties of compounds

Creating iron sulphide

Creating iron sulphide

Creating iron sulphide

Chemical bonds

Chemical formulae

Formula and formulae

Numbers in formulae

Formulae are always the same

The reactivity series