Arnold House School

Chemical words that are often confused

Physical changes / reactions

no new substances are made
may be a change in appearance or state
may be easily reversed to obtain the original substances
mass is conserved i.e. doesn't change

e.g. change of state solid <–––> liquid <–––> gas
dissolving solute + solvent <–––> solution

Chemical changes

one or more new substances are made
may change in appearance or physical properties
e.g. change of colour, gas produced
not easily reversible i.e. usually difficult to return to the original substance
mass is conserved i.e. doesn't change

Melting (liquefying) changing from solid to liquid at its melting point

Evaporation changing from liquid to gas (vapour)

Boiling changing from liquid to gas (vapour) at the boiling point

Condensation changing from gas (vapour) to liquid.

Freezing (solidifying) changing from liquid to solid at its freezing point

Sublimation changing directly from solid to gas or gas to solid e.g. solid carbon dioxide, iodine, ammonium chloride.

Dissolving mixing a liquid solvent and a solute to form a clear solution.

Solvent the liquid that does the dissolving e.g. water, alcohol (ethanol), propanone (acetone), white spirit

Solute the substance that is dissolved

e.g. solid – salt, sugar, copper sulphate in water;

chlorophyll, iodine in alcohol;

liquid – alcohol in water; oil in alcohol;

gas – oxygen, carbon dioxide in water.

Solution The clear liquid mixture e.g. salt or sugar solution,

though it may be coloured e.g. copper sulphate solution,

iodine solution.

Suspension The cloudy mixture produced when the solid doesn't dissolve.

Decant To allow the heavier particles to settle to the bottom (sediment), so the clearer liquid can be poured off the top.

Filtrate The clear liquid that passes through the filter paper

after filtering a suspension

Residue Solids left behind (e.g. in the filter paper)

Distillate Pure liquid produced when a solution is distilled (boiled then condensed)

Chemical Reactions

Oxidation addition of oxygen

Reduction removal of oxygen

e.g. iron oxide+ carbon ––> iron + carbon dioxide

(In Blast furnace the carbon (coke) is oxidized and the metal oxide reduced)

Combustion (burning) The oxidation of a fuel resulting in heat production

carbon + oxygen ––> carbon dioxide

hydrogen + oxygen ––> hydrogen oxide (water!)

hydrocarbon ––> water + carbon dioxide

e.g. coal, methane, butane, alcohol, wax, wood etc.

Respiration The oxidation of a food resulting in energy production

but not as much heat energy as burning

sugar + oxygen ––> water + carbon dioxide + ENERGY

Neutralisation the reaction of an acid with a base to produce a neutral solution

Displacement when an element (usually a metal) higher up the reactivity series reacts and replaces an element in a compound, lower down the series.

Decomposition (thermal) breakdown of a compound into simpler substances (using heat)

Acid A chemical with a sour taste; pH 1–6; in concentrated solutions may be corrosive.

Base The opposite to an acid; will neutralise an acid to give a neutral solution pH 7; insoluble bases have no pH as they don't dissolve in water!

Alkali A soluble base ; pH 8–14.

pH scale Scale from 1–14 to determine how acid or alkaline a solution is; measured with universal indicator paper or a pH meter.

Non–metal oxides are acidic e.g. carbon dioxide, sulphur dioxide, nitrogen oxides.

Metal oxides are basic; some are insoluble e.g. copper oxide, lead oxide, iron oxide; others are soluble i.e. alkali e.g. sodium oxide, calcium oxide.

Further Chemistry Reading

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