TRIPLE: 1.54 describe experiments to investigate electrolysis, using inert electrodes, of aqueous solutions such as sodium chloride, copper(II) sulfate and dilute sulfuric acid and predict the products

Electrolysis of aqueous sodium chloride using inert electrodes

Suitable materials for the electrodes are platinum or graphie

Particles present in solution: 

• Sodium ions
• Chloride ions
• Water molecules 

Hydrogen gas is produced as water molecules gain electrons at the cathode.

Chlorine gas is produced as chloride ions lose electrons.

1.52 understand that electrolysis involves the formation of new substances when ionic compounds conduct electricity

The products of electrolysing a molten binary compound (a compound only containing two elements) can easily be predicted by using the following rules:

• The metal is formed at the negative electrode (cathode)
• The non-metal is formed at the positive electrode (anode)

E.g. With molten lead (II) bromide, lead is formed at the negative electrode and bromine is formed at the positive electrode.

1.51 describe experiments to distinguish between electrolytes and non electrolytes

1. Set up a circuit with an LED (light emitting diode) and a break in the circuit.

2. Put both ends of the wire in a molten substance.

3. If the LED gives out light when a current is flowing, and electrolyte is present because the solution is conducting.

1.50 understand why ionic compounds conduct electricity only when molten or in solution

Ionic compounds do not conduct electricity when solid since ions are not free to move.

However, ionic compounds do conduct electricity when molten or when in aqueous solution (i.e. when dissolved in water).

When an electric current is passed through a molten ionic compound, or through an aqueous solution of an ionic compound, electrolysis takes place.

1.49 understand why covalent compounds do not conduct electricity

In a covalent compound, there are no delocalised electrons, so it cannot hold a current. Graphite is an exception, as this is a giant covalent structure and has the 4th electron free to move, so graphite can conduct electricity.