Practical: Investigate the Electrolysis of Aqueous Solutions (Edexcel IGCSE Chemistry)

Aim:

To electrolyse aqueous solutions of sodium chloride, sulfuric acid and copper(II)sulfate, and to collect and identify the products at each electrode

Diagram:

Electrolysis cell for collecting gaseous products from aqueous solutions

Method:

1. Add the aqueous solution to a beaker and cover the electrodes with the solution
2. Invert two small test tubes to collect any gaseous products
3. Connect the electrodes to a power pack or battery
4. Turn on the power pack or battery and allow electrolysis to take place
5. Observations at each electrode are made
6. Gases collected in the test tube can be tested and identified

Testing the products

• If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint, the gas is hydrogen
• If the gas produced at the anode relights a glowing splint dipped into a sample of the gas, the gas is oxygen
• If the anode gas bleaches of a piece of litmus paper, chlorine has been produced
• If a solid forms around the electrode, the metal have been formed
  • The colour can indicate the metal formed

Results:

Solution	Cathode observation	Anode observation
Sodium chloride	Colourless gas evolved which goes 'pop' with a lighted splint	Gas evolved which bleaches litmus paper
Dilute sulfuric acid	Colourless gas evolved which goes 'pop' with a lighted splint	Colourless gas evolved which relights a glowing splint
Copper(II) sulfate	Pink-brown deposit seen on the electrode	Colourless gas evolved which relights a glowing splint

Conclusions:

1. Sodium chloride solutions produces hydrogen at the cathode and chlorine at the anode
2. Dilute sulfuric acid produces hydrogen at the cathode and oxygen at the anode
3. Copper(II)sulfate solution produces copper at the cathode and oxygen at the anode