Glossaries‎ > ‎

Chemical Terms


Acids: Proton donors.

Acid rain
: Rain that has a higher hydrogen ion concentration than normal (pH less than 5).

Acidic oxides
: Oxides that display one or both of the following properties:
  • React with bases to form salts.
  • React with water to produce acids.

Acidic salts: Salts that dissolve in water to form solutions with a pH less than 7.

Acidity: A measure of the concentration of hydrogen ions (measured in pH).

Activity Series
: A series of metals arranged from the most reactive (the most easily oxidised) to the least reactive (the least easily oxidised).

Addition Polymer
: A polymer formed by molecules adding together without the loss of any atoms. No other product is formed in addition polymerisation.

Addition Reaction
: A reaction in which two or more molecules are reacted together to form a single molecule.

Aeration (of water): The increasing of dissolved oxygen by spraying, which causes iron salts to be oxidised to insoluble oxides.

Alkanoic acid: An alkane containing carboxylic acid functional group (–COOH) in place of three hydrogen atoms, which can lose a hydrogen ion and behave as a weak acid.

Alkanol: An alkane containing a hydroxy/alcohol functional group (–OH) in place of a hydrogen atom, which gives the molecule high melting and boiling points.

Allotropy: The existence of two or more alternative forms of the same element in the same physical state.

Amphoteric oxides: Oxides that react with both acids and bases.

Amphiprotic substance: A molecule or ion that can behave as either a proton donor or a proton accepter.

Anode: The negative electrode, at which oxidation occurs.

Atmosphere: The gaseous mixture surrounding the surface of the Earth.

Atomic absorption spectroscopy (AAS): A technique used to identify the presence and concentration of substances by analysing the spectrum produced when a substance is vaporised and absorbs certain frequencies of light.


Bases: Proton acceptors.

Basic oxides
: Oxides that display the following properties:
  • React with acids to produce salts.
  • If soluble, react with water to produce alkaline solutions.
  • Do not react with alkaline solutions.

Basic salts: Salts that dissolve in water to form solutions with a pH greater than 7.

Biochemical oxygen demand (BOD): A measure of the concentration of dissolved oxygen that is needed for the complete breakdown of the organic matter in a sample by aerobic bacteria (generally measured in ppm).

: Material produced by living organisms.

: A polymer that is made totally or in large part by living organisms.

Bromothymol blue: A synthetic indicator than changes colour around the neutral range.

Buffer system: A solution that controls its acidity, such that if an acid or a base is added, there is a minimal change in pH.

Burette: A volumetric glassware item used to transfer one solution into another at a controlled rate.


Catalyst: A substance that increases the rate of a reaction and which is recoverable at the end unchanged in chemical composition or mass.

Catalytic Cracking
: The process in which high molecular weight (high boiling point) fractions from crude oil are broken into lower molecular weight (lower boiling point) substances in the presence of high temperatures and a catalyst.

Cathode: The positive electrode, at which reduction occurs.

Chlorination (of water): The disinfecting of water using chlorine gas and various hypochlorites, which kill microorganisms.

Chlorofluorocarbon (CFC): A haloalkane that contains both fluorine and chlorine atoms, and no hydrogen atoms.

Commercial radioisotopes: Radioisotopes that are used in medicine, industry and/or scientific research.

Concentrated solution: A solution in which the total concentration of acid is high (a large amount of solute is contained in a small amount of solution).

Conceptual definitions: Definitions that attempt to explain observations.

Condensation Polymer: A polymer formed by a condensation reaction, involving the elimination of a small molecule (often water) when pairs of monomer molecules join together.

Conjugate acid: The substance formed from a base when it accepts a proton.

Conjugate base: The substance formed from an acid when it gives up a proton.

Coordinate covalent bond: A covalent bond in which one of the two atoms bonded supplies all of the shared electrons.

Covalent bond: A chemical bond formed between two atoms through the sharing of pairs of electrons.


Decomposition: The breakdown of a substance into two or more simpler substances.

Dehydration: The process of removing water molecules, or the equivalent of water molecules, from a substance.

Dilute solution: A solution in which the total concentration of acid is low (a small amount of solute is contained in a large amount of solution).

Diprotic acids: Acids that can release up to two protons, or hydrogen ions, per molecule.

Displacement Reaction: A reaction in which a more reactive metal converts the ion of a less reactive metal to the neutral atom.

Dissolved oxygen (DO): A measure of the concentration of oxygen (generally measured in ppm).

Double covalent bond: A covalent bond involving the sharing of two pairs of electrons.


Electrode: A conductor, which allows electrons to pass from the external circuit to a half-cell or vice versa.

Electrolyte: An aqueous or molten substance that conducts electricity.

Equilibrium: The state reached when the rate of forward and reverse reactions in a closed system become equal.

Esterification: The process in which an alcohol and an acid are converted to an ester and water.

Eutrophication: The abundant growth of aquatic plants due to nutrient-enriched conditions, in particular, nitrate and phosphate enriched conditions.


Fermentation: The process of converting organic compounds into simpler substances using organisms such as yeasts and bacteria.

Filtration (of water): Formation of clear water by removal of substances that cause turbidity and colouration, using beds of sand and gravel as well as charcoal filters.

Flocculation (of water): The coagulation of colloidal and particulate matter to form flocs.

Fluoridation (of water): Adding of fluoride compounds to help prevent tooth decay (resulting in a fluoride concentration of about 1 ppm).

Free radical: A species containing at least one unpaired electron.

Functional group: An atom or a group of atoms that reacts in a characteristic way when in different carbon compounds.


Galvanic Cell: A cell capable of producing an electric current from a redox reaction that occurs within it.

Gravimetric Analysis: A method of quantitative analysis that involves the precipitation of a highly insoluble compound followed by weighing of the dried precipitate formed.


Haber Process: The industrial synthesis of ammonia.

Haloalkane: An alkane containing at least one halogen functional group.

Halon: Also referred to as a brominated CFC, a haloalkane that contains bromine, chlorine and/or fluorine atoms, and no hydrogen atoms.

Hardness: A measure of the concentration of calcium and magnesium ions.

Heavy Metal: A metal with a relative density of 5.0 or higher.

: The process of adding water molecules, or the equivalent of water molecules, to a substance.

Hydrocarbon: A compound containing only hydrogen and carbon.

Hydrochlorofluorocarbon (HCFC): A haloalkane containing hydrogen, chlorine and fluorine atoms.

Hydrofluorocarbon (HFC): A haloalkane containing hydrogen and fluorine atoms.


Indicator: A chemical that change colour as the concentration of hydrogen ions in a solution changes.

Indicator range: The range of acidity or basicity over which the colour of an indicator changes colour.

Isomer: One of a series of compounds that have the same molecular formula, but different structural formulae.

: Atoms with the same number of protons, but with different numbers of neutrons.




Le Chatelier's Principle: “When a change is made to an equilibrium system, the system moves to counteract the imposed change and restore the system to equilibrium.”

: A dye extracted from various species of lichen that changes colour around the neutral range.


Membrane Filter: A thin film of synthetic polymer through which there are pores of reasonably uniform size.

Methyl orange: A synthetic indicator that changes colour in the acidic range.

Molar Heat of Combustion
: The heat liberated when one mole of a certain compound undergoes complete combustion with oxygen at a constant pressure of exactly one atmosphere (100 kPa) and at 25°C with the final products being carbon dioxide gas and liquid water.

: A relatively simple molecule from which a polymer can be made.

Monoprotic acids: Acids that can release only one proton, or hydrogen ion, per molecule.


Neutral oxides: Oxides that do not react with either acids or bases.

Neutral salts: Salts that dissolve in water to form solutions that have a pH close to 7.

Neutralisation: The proton transfer reaction between an acid and a base to produce a salt and water.

Non-renewable Resource
: A resource that cannot be regenerated and hence cannot last indefinitely.


Operational definitions: Definitions based entirely on particular observations.

: Loss of electrons.

Oxidation state: A measure of a chemical species’ degree of oxidation.

Ozone holes: Marked decreases in the concentration of ozone in the ozone layer above the north and south poles.


Petrochemical: A chemical derived from petroleum.

pH Adjustment (of water): The adjustment of pH to between 7 and 8.5 using buffering chemicals.

Phenolphthalein: A synthetic indicator that changes colour in the basic range.

Pipette: A volumetric glassware item used to transfer a known volume of a solution into a conical flask.

Polyhydroxylalkanoates (PHAs): biopolymers, produced by microorganisms, that have very similar properties to polypropylene.

: A large molecule in which one or more monomers are repeated.

Polymerisation: The reaction of monomers to form a polymer.

Primary standard solution: A solution prepared from a solid that:
  • Is water-soluble.
  • Has a high purity.
  • Has a known formula.
  • Is stable in air.



Radioisotopes: Isotopes that have unstable nuclei and emit radiation.

Rate of reaction: The rate of change of concentration.

Redox (Reduction-Oxidation) Reaction: A reaction in which both oxidation and reduction occur, and hence transfer of electrons occurs.

: Gain of electrons.

Refluxing: The process of heating a reaction mixture in a vessel with a condenser tube attached.

Renewable Resource
: A resource that can be regenerated and hence can last indefinitely.


Saturated: Containing only single carbon-to-carbon bonds.

Screening (of water): The removal of large debris.

Secondary standard solution:  A solution that has had its concentration determined by a titration with a primary standard solution.

Sedimentation (of water): The settling of flocs to form a sludge.

Single covalent bond: A covalent bond involving the sharing of one pair of electrons.

Spectroscopy: The study of the interaction of electromagnetic radiation with matter.

Stable isotopes: Isotopes that have stable nuclei and do not emit radiation.

Standard solution: A solution with an accurately known concentration.

Steam Thermal Cracking
: The process in which ethane gas or larger hydrocarbons are mixed with steam and passed through hot metal coils, producing ethylene.

Strong acid: An acid that completely ionises in water to form hydrogen ions, leaving no neutral acid molecules remaining.


Table of standard potentials: A table that lists common reduction half-equations along with the potentials of the half-equations, known as reduction potentials, relative to the standard hydrogen electrode.

Titration: A volumetric analytical technique used to determine the concentration of a solution by reacting it with a standard solution.

Total dissolved solids (TDS): A measure the mass of solids dissolved in a unit volume of water (generally measured in ppm).

Total Ozone Mapping Spectrophotometers (TOMS): Instruments used onboard satellites to scan through the atmosphere and measure ozone concentration as a function of altitude and geographical position.

Transuranic elements: Elements beyond uranium in the periodic table (having atomic numbers greater than 92).

Triprotic acids: Acids that can release up to three protons, or hydrogen ions, per molecule.

Turbidity: A measure of the amount of colloidal suspended matter, which translates into a degree of cloudiness or transparency (measured in relative units called nephelometric turbidity units, or NTUs).


Ultraviolet spectrophotometer: An instrument that measures the intensity of radiation in the ultraviolet wavelengths.

: Containing at least one double carbon-to-carbon bond.



Weak acid: An acid that only partially ionises in water to from hydrogen ions, leaving neutral molecules remaining.




: The inorganic compounds (aluminosilicates) used as catalysts for cracking alkanes.