e–GlossaryA

AcidAn acid is a substance that contains hydrogen ions, H+, as the only positive ions in an aqueous solution.

Acid-base titrationA quantitative experimental technique used to carry out complete neutralisation reaction between an acid and an alkali

Activation energyMinimum energy the reactant particles must have before effective collision between them can result in a chemical reaction

AlcoholA homologous series containing the hydroxyl group, –OH, with the general formula CnH2n+1OH, where n = 1, 2, 3, …

AlkaliA base that is soluble in water

AlkaneAlkanes are saturated hydrocarbons with the general formula CnH2n+2, where n = 1, 2, 3, …

AlkeneAlkenes are unsaturated hydrocarbons with the general formula CnH2n, where n = 2, 3, 4, …

AlloyA mixture of two or more metals (sometimes non-metals) in a specific proportion. The added metals are usually in small amounts

AnalgesicA modern medicine that relieves pain

AnionThe negative ion that is formed when an atom gains electrons

AnodeAn electrode which is connected to the positive terminal of a battery

AntibioticA modern medicine that kills bacteria

AntioxidantA food additive that prevents oxidation of food

AtomThe smallest particle of an element that can participate in a chemical reaction

Avogadro constantThe number of particles in one mole of any substance, which refers to the value of 6.02 × 1023 mol-1

BBase

A substance that reacts with an acid to give only a salt and water

CCarbon compound

A compound that contains carbon combined with other elements

Carboxylic acidA homologous series containing the carboxyl group, –COOH, with the general formula CnH2n+1COOH, where n = 0, 1, 2, …

CatalystA substance which increases the rate of a chemical reaction, without itself being chemically changed at the end of the reaction

CathodeAn electrode which is connected to the negative terminal of a battery

CationThe positive ion that is formed when an atom loses electrons

Coagulation of latexSeparation of rubber molecules from the water in the latex

Collision theoryA theory used to explain the rate of chemical reactions in terms of effective collisions between particles

Composite materialAn advanced material that is formed by combining two or more different materials. The properties of this new material are more superior compared to those of its original materials

CompoundA substance that contains two or more elements that are chemically bonded

ConcentrationThe concentration of a solution is the amount of a solute that dissolved in a unit volume of a solution. The concentration of a solution can be expressed in terms of gram of solute per litre (dm3) of a solution, g dm-3, or number of moles of solute per litre (dm-3) of solution, mol dm-3

CondensationProcess of changing gas to liquid

ConductorA substance which conducts electricity but does not change chemically during the conduction

Contact processAn industrial process to manufacture sulphuric acid from sulphur

Covalent bondA bond that is formed between atoms of non-metals by overlapping their outermost shells. In covalent bonding, each atom in a molecule contributes an equal number of electrons for sharing.

CrystallisationA technique used to prepare crystals of a substance from its saturated solution

DDecomposition

A chemical reaction in which a compound is broken down into simpler substances

DehydrationA reaction where water molecules are removed from the reactants

DetergentThe sodium salt formed when an alkyl hydrogen sulphate is neutralised by an alkali (sodium hydroxide)

DiffusionThe movement of particles of a substance from higher concentration to a medium of lower concentration

DilutionAddition of a solvent to a more concentrated solution to produce a more diluted solution

DistillationProcess of extracting a substance by vapourising it and then condensing the vapour at a fixed temperature

DyeA food additive that colours food or replaces lost colours

EElectrochemical series

A list of metals arranged in descending order of their atomsí tendency to lose electrons to form positive ions. The more electropositive metals are placed higher up in the series.

ElectrodeAn electric conductor which carries electric current in and out of an electrolyte

ElectrolysisThe conductivity of electricity in an electrolyte, leading to its decomposition to its constituent elements

ElectrolyteElectrolytes are compounds that conduct electricity in a molten state or in an

aqueous solution and are decomposed to their constituent elements in the process.

ElectronA negatively-charged subatomic particle that surrounds the nucleus of an atom

Electron arrangementThe way electrons are arranged in an atom

Empirical formulaThe chemical formula which shows the simplest whole number ratio of the atoms of each element present in a compound

Endothermic reactionA chemical reaction that absorbs heat energy from the surroundings

Energy level diagramA graph that shows the energy content of reactants and products with the energy change of a chemical reaction

Energy profile diagramA graph that shows the energy change as reactants change to become products in a chemical reaction

EsterA homologous series containing the carboxylate group, –COO–, with the general formula CnH2n+1COOCmH2m+1, where n = 0, 1, 2, … and m = 1, 2, 3, …

EsterificationThe reaction between a carboxylic acid and an alcohol to form an ester and water. The reaction is catalysed by concentrated sulphuric acid.

EvaporationThe change of a liquid into a gas at the surface of a liquid

Exothermic reactionA chemical reaction that releases heat energy to the surroundings

Extraction of metalThe process of obtaining a metal from its ore

FFat

A natural ester of fatty acid and glycerol

Fatty acidA carboxylic acid that has a long chain of about 10 to 20 carbon atoms. It has only one carboxyl group.

FermentationThe reaction in which yeast converts glucose into ethanol

FiltrationThe separation of a solid and a liquid by pouring the mixture into a porous material such as filter paper. The liquid passing through the filter paper is called filtrate. The solid trapped on the filter paper is called the residue.

Flavouring agentA food additive that gives flavour to food or enhances its natural flavour

Food additiveAny substance that is added to food to preserve it or improve its flavour and appearance

Fractional distillationThe separation of two liquids with different boiling points by distillation using a fractionating column

Functional groupAn atom or a group of atoms that is responsible for the characteristic chemical properties of an organic compound

GGlycerol

An alcohol that has three hydroxyl groups

GroupThe vertical columns of elements in the Periodic Table. The group number is determined by the number of valence electrons in the atoms of the elements

HHaber process

An industrial process to manufacture ammonia from nitrogen and hydrogen

Half-equationAn ionic equation showing either oxidation or reduction that explicitly shows the electrons involved

Heat of combustionThe amount of heat given off when one mole of a substance is completely burnt in excess oxygen

Heat of displacementThe amount of heat energy given off when one mole of metal is displaced from its aqueous solution (by the more electropositive metal) under standard conditions

Heat of neutralisationThe amount of heat given off when one mole of water is produced from the neutralisation reaction between an acid and an alkali under standard conditions

Heat of precipitationThe amount of heat given off when one mole of precipitate is formed when mixing the aqueous solutions of the ions of insoluble salt under standard conditions

Homologous seriesA family of organic compounds with each member of the family differing from the previous member by having one more group of atoms –CH2–

HydrationA reaction where water molecules are added to a compound

HydrocarbonOrganic compounds that contain hydrogen and carbon atoms only

HydrogenationThe addition of a hydrogen molecule to the carbon atom of the double bond

HydrolysisA reaction of a compound with water to produce smaller products

IIon

A positively-charged or negatively-charged particle formed as a result of losing electrons or gaining electrons in an atom

Ionic bondA bond that is formed when electrons are transferred from metal atoms to non-metal atoms to form positive and negative ions. The ionic bond is the strong electrostatic forces of attraction between positive and negative ions.

IsomerIsomers are different compounds that have the same molecular formula but different structural formula

IsotopeAtoms of the same element but are different in the number of neutrons

MMatter

Anything that occupies space and has a mass

MeltingThe change of a solid into a liquid

Molar massThe mass of one mole of any substance

Molar volumeThe volume occupied by one mole of any gas, which is 22.4 dm3 at s.t.p. or 24 dm3 at room conditions

MolarityThe number of moles of solute present in 1 dm3 of solution

MoleA basic S.I. unit used to measure the amount of substances. One mole of substance contains as many particles as the number of atoms in 12 g of carbon-12.

MoleculeA group of two or more atoms which are chemically bonded together

Molecular formulaThe chemical formula which shows the actual number of atoms of each element in a molecule

MonomerThe smaller molecules that make up the repeating units in polymers

NNeutralisation

The reaction between an acid and a base (or alkali) to produce only water and a salt

NeutronAn electrically neutral subatomic particle found in the nucleus of an atom

Noble gasA gas that is inert and monoatomic because it has stable electronic structures (octet or duplet)

Non-electrolyteA substance that does not conduct electricity even in a molten state or in an aqueous solution

Non-hydrocarbonOrganic compounds containing other elements such as nitrogen and oxygen besides hydrogen and carbon

Nucleon numberThe total number of protons and neutrons in the nucleus of an atom

NucleusThe central part of an atom consisting of neutrons and protons

OOrganic compound

A carbon compound that is derived or obtained from living or once living things

OxidationOxidation occurs when there is a gain in oxygen, a loss of hydrogen, a loss of electrons or an increase in the oxidation number of a substance

Oxidation numberThe imaginary change of an atom if it exists as an ion

Oxidising agentA substance that oxidises another substance and is reduced in the redox reaction

PPeriod

The horizontal rows of elements in the Periodic Table. The period number is determined by the number of electron-filled shells in atoms of the elements.

pH scaleA measure of how acidic or alkaline an aqueous solution is

PolymerMolecules that consist of a large number of small identical units joined together repeatedly

PolymerisationThe process of joining together a large number of small molecules to form polymers

PrecipitateAn insoluble solid produced from a solution during a chemical reaction

PreservativeA food additive that prevents or slows down spoilage of food

ProtonA positively-charged subatomic particle found in the nucleus of an atom

Proton numberThe number of protons in an atom

RRate of reaction

The rate of a chemical reaction is determined by measuring how quickly a reactant is used up or how quickly a product is produced over a period of time

Reactivity series of metalsA list where metals are placed in the order of their reactivity with oxygen

Redox reactionA reaction in which oxidation and reduction occur spontaneously

Reducing agentA substance that reduces another substance and is oxidised in the redox reaction

ReductionReduction occurs when there is a loss of oxygen, a gain in hydrogen, a gain in electrons or a decrease in the oxidation number of a substance

Relative atomic massThe relative atomic mass of an element is defined as the average mass of one atom of that element compared with of the mass of a carbon-12 atom

Relative formula massThe relative formula mass of a substance is defined as the average mass of one formula unit of an ionic substance compared with of the mass of a carbon-12 atom

Relative molecular massThe relative molecular mass of a substance is defined as the average mass of a molecule of that substance compared with of the mass of a carbon-12 atom

SSalt

A compound formed when the hydrogen ion of an acid is replaced by a metal ion or an ammonium ion

SaponificationSaponification is hydrolysis of an ester by a hot aqueous alkali solution to form an alcohol and sodium (or potassium) salts of carboxylic acids

Scientific methodA systematic approach used by scientists to investigate a phenomenon

Semi-metalAn element that possesses the intermediate properties between metals and non-metals

ShellThe orbit surrounding the nucleus of an atom in which electrons move

SoapThe sodium or potassium salt of a fatty acid

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StabiliserFood additives that improve the texture and consistency of food

StoichiometryThe relationship between the amount (usually in mole) of reactants and products involved in a chemical reaction

Structural formulaA formula that shows how atoms are bonded to each other in a molecule

SublimationThe change from a solid into a gas without going through liquid state

Substitution reactionA reaction in which one atom replaces another atom of a molecule

TTitration

A laboratory technique in which a standard solution is used to determine the concentration of an unknown solution using an indicator to detect the end point during neutralisation

Transition elementAn element in Group 3 to Group 12 of the Periodic Table

VValence electrons

The electrons in the outermost shell of an atom

ViscocityA measure of the resistance of fluids to flow

Voltaic cellA cell that produces electrical energy by means of chemical reaction. It converts chemical energy to electrical energy. It is also known as an electrochemical cell or a galvanic cell.

VulcanisationThe process of treating natural rubber with sulphur to form vulcanised rubber

WWhitening agent

A detergent additive that makes clothes look white and cleaner