Chemical Changes Mind Map (GCSE)

From most to least reactive: potassium, sodium, lithium, calcium, magnesium, (carbon), zinc, iron, (hydrogen), copper. Carbon and hydrogen are included for comparison.

The more reactive the metal, the more vigorously it reacts with water and acids. Metals above hydrogen react with acids to release hydrogen gas.

A more reactive metal displaces a less reactive metal from its compound. For example, iron displaces copper from copper sulfate solution.

Metals reacting with oxygen form metal oxides: this is oxidation. Removing oxygen is reduction. Higher tier: oxidation is loss of electrons, reduction is gain (OIL RIG).

Unreactive metals such as gold are found in the Earth as the metal itself.

Metals less reactive than carbon are extracted by heating their oxides with carbon. For example, iron oxide + carbon → iron + carbon dioxide.

Metals more reactive than carbon, such as aluminium, are extracted by electrolysis, which uses large amounts of energy and is expensive.

acid + metal → salt + hydrogen. Test for hydrogen: a lighted splint gives a squeaky pop.

acid + metal oxide or metal hydroxide → salt + water. Bases neutralise acids; soluble bases are called alkalis.

acid + metal carbonate → salt + water + carbon dioxide. Test for carbon dioxide: it turns limewater milky.

• Hydrochloric acid makes chlorides
• Sulfuric acid makes sulfates
• Nitric acid makes nitrates

Required practical (AQA) and core practical (Edexcel). Warm dilute sulfuric acid, add copper oxide until no more dissolves (it is in excess), filter out the excess, then gently evaporate and leave the solution to crystallise into copper sulfate crystals.

From 0 to 14. Below 7 is acidic, 7 is neutral and above 7 is alkaline. Measure it with universal indicator or a pH probe.

Acids produce hydrogen ions (H⁺) in water; alkalis produce hydroxide ions (OH⁻).

Hydrogen ions and hydroxide ions react to form water: H⁺ + OH⁻ → H₂O.

Higher tier. Strong acids, such as hydrochloric, nitric and sulfuric, are completely ionised in water. Weak acids, such as ethanoic, citric and carbonic, are only partially ionised. Strong is not the same as concentrated.

Positive ions move to the negative electrode (cathode); negative ions move to the positive electrode (anode). The ions are discharged there as elements.

The metal forms at the cathode and the non-metal at the anode. Molten lead bromide gives lead and bromine.

Aluminium oxide is dissolved in cryolite to lower its melting point and save energy. Aluminium forms at the cathode; oxygen at the anode reacts with the carbon anodes, so they must be replaced.

• At the cathode: hydrogen forms if the metal is more reactive than hydrogen; otherwise the metal forms
• At the anode: oxygen forms, unless the solution contains halide ions, when the halogen forms

Brine gives hydrogen, chlorine and sodium hydroxide solution.

Required practical (AQA) and core practical (Edexcel): electrolyse aqueous solutions with inert electrodes and identify the products, for example copper sulfate solution, where copper forms at the cathode.

• Hydrogen: squeaky pop with a lighted splint
• Oxygen: relights a glowing splint
• Carbon dioxide: turns limewater milky
• Chlorine: bleaches damp litmus paper

Higher tier. Show what happens at each electrode, for example Cu²⁺ + 2e⁻ → Cu at the cathode.

Higher tier. Show only the ions that react, for example in displacement and neutralisation.