Electrolysis

Question 1

Why does an ionic substance need to be molten or in solution before you can electrolyse it?

Answer 1

An electric current can only pass through an ionic substance when its ions are free to move about.

Question 2

Describe how you would set up the equipment for the electrolysis of a solution of aqueous copper sulfate.

Answer 2

• Connect each electrode to the power supply.
• Place the electrodes into a beaker containing a solution of aqueous copper sulfate, making sure that the electrodes aren’t touching each other.
• Turn the power supply on.

Question 3

Explain what determines the product formed at the cathode when you electrolyse an aqueous solution.

Answer 3

The position of the metal in the reactivity series.

Question 4

What is formed at the anode when a concentrated halide solution is electrolysed?

Answer 4

The halogen will be formed at the anode.

Question 5

Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.
What would you see happening at the anode? Explain your answer.
[2 marks]

Answer 5

• At the anode, you would see bubbles of gas appearing…

- …because chloride ions are losing electrons to form chlorine.

Question 6

Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.
What would you see happening at the cathode? Explain your answer.
[2 marks]

Answer 6

• At the cathode, you would see the electrode being plated…
• …because copper ions are gaining electrons to form copper metal.

Question 7

A student carries out an electrolysis of a dilute solution of magnesium chloride, MgCl₂(aq).
Write the half-equation for the reaction that occurs at the cathode.
[1 mark]

Answer 7

2H⁺(aq) + 2e⁻ → H₂(g)

Question 8

A student carries out an electrolysis of a dilute solution of magnesium chloride, MgCl₂(aq).
Write the half-equation for the reaction that occurs at the anode.
[1 mark]

Answer 8

4OH⁻(aq) → O₂(g) + H₂O(l) + 4e⁻