Chemical changes

Reactivity Series

➤ A list of metals (and carbon & hydrogen) in order of how easily they form positive ions.

Displacement Reaction

➤ A more reactive metal displaces a less reactive one from its compound.

Oxidation

➤ Loss of electrons OR gain of oxygen.

Reduction

➤ Gain of electrons OR loss of oxygen.

Redox Reaction

➤ A reaction in which one substance is oxidised and another is reduced.

What happens when a metal reacts with acid?

➤ Metal + Acid → Salt + Hydrogen

What gas is released when metals react with acids?

➤ Hydrogen gas (test: makes a squeaky pop with a lit splint)

What does a more reactive metal do in a displacement reaction?

➤ It displaces a less reactive metal from its compound.

Is iron reduced or oxidised when it reacts with copper sulfate?

➤ Iron is oxidised (loses electrons), copper is reduced.

Which is more reactive: magnesium or zinc?

➤ Magnesium

Acid

➤ A substance that releases H⁺ ions in solution.

Alkali

➤ A base that dissolves in water to form OH⁻ ions.

Neutralisation

➤ A reaction between an acid and a base to form a salt and water.

What is the general word equation for neutralisation?

➤ Acid + Base → Salt + Water

What is the ionic equation for neutralisation?

➤ H⁺ + OH⁻ → H₂O

What salt is made when hydrochloric acid reacts with sodium hydroxide?

➤ Sodium chloride

How is a salt named?

➤ First part: metal/base, second part: acid used
(e.g. copper oxide + sulfuric acid → copper sulfate)

Electrolysis

➤ The decomposition of an ionic compound using electricity.

Electrode

➤ A conductor through which electricity enters or leaves the electrolyte.

Anode

➤ The positive electrode (where oxidation occurs).

Cathode

➤ The negative electrode (where reduction occurs).

Electrolyte

➤ A molten or dissolved ionic compound that can conduct electricity.

Inert Electrode

➤ An electrode that does not react, usually made from graphite or platinum.

What happens to positive ions in electrolysis?

➤ They are reduced (gain electrons) at the cathode.

What happens to negative ions?

➤ They are oxidised (lose electrons) at the anode.

Write the half equation for the reduction of Pb²⁺ ions.

➤ Pb²⁺ + 2e⁻ → Pb

What product forms at the anode during the electrolysis of molten lead bromide?

➤ Bromine gas (Br₂)

Electrolysis of Aqueous Solutions

• In aqueous solutions, water also ionises into H⁺ and OH⁻

• At the cathode:

  • If metal is more reactive than hydrogen, hydrogen is produced

• At the anode:

  • If solution contains halide ions, halogen is produced

  • Otherwise, oxygen gas is produced

Electrolytic Extraction

➤ Using electrolysis to extract metals more reactive than carbon (e.g. aluminium).

Cryolite

➤ A substance used to lower the melting point of aluminium oxide in electrolysis.

Why is electrolysis used to extract aluminium?

➤ Because aluminium is more reactive than carbon, so cannot be extracted by reduction.

What are the electrodes made of in aluminium extraction?

➤ Graphite

Why do the anodes need replacing regularly?

➤ Oxygen reacts with graphite to form CO₂.