Chemical Changes Definitions

Flashcards for AQA Chemistry GCSE Topic 4 - Chemical Changes

Acid

Acids produce hydrogen ions (H+) in aqueous solutions. They have a pH range of 0-6.

Alkali

Alkalis produce hydroxide ions (OH-) in aqueous solutions. They have a pH range of 8-14.

Crystallisation

A separation technique used to produce solid crystals from a solution by evaporating the solvent.

Displacement

A chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Electrolysis

The splitting up of an ionic compound using electricity. The electric current is passed through a substance causing chemical reactions at the electrodes and the decomposition of the materials.

Electrolyte

A solution containing free ions from the molten or dissolved ionic substance. The ions are free to move to carry charge.

Extraction

Extraction techniques are used to separate a desired substance when it is mixed with others.

Filtration

A separation technique used to separate solids from liquids.

Negative electrode (cathode)

The electrode where hydrogen is produced if the metal in the electrolyte is more reactive than hydrogen. It is where positively charged ions gain electrons and so the reactions are reductions.

Neutralisation

The reaction when an acid and a base react to form water and a salt.

Oxidation

A reaction involving the gain of oxygen. Oxidation is the loss of electrons.

pH scale

The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.

Positive electrode (anode)

The electrode where oxygen is produced unless the solution contains halide ions then the halogen is produced. It is where negatively charged ions lose electrons and so the reactions are oxidations.

Redox reaction

A reaction in which both oxidation and reduction occur simultaneously.

Reduction

A reaction involving the loss of oxygen. Reduction is the gain of electrons.

Reduction with carbon

Metals less reactive than carbon can be extracted from their oxides by reduction with carbon.

Strong acid

A strong acid is completely ionised in aqueous solution. Examples of strong acids are hydrochloric, nitric and sulfuric acids.

The reactivity series

Metals are arranged in order of their reactivity in a reactivity series. This can be used to predict products from reactions.

Titration

A technique used where a solution of known concentration is used to determine the concentration of an unknown solution.

Universal indicator

A mixture of dyes that changes colour gradually over a range of pH and is used in testing for acids and alkalis.

Weak acid

A weak acid is only partially ionised in aqueous solution. Examples of weak acids are ethanoic, citric and carbonic acids.