CP 4 - Electrolysis of Copper Sulfate Solution

Question 1

What colour is CuSO4(aq)?

Answer 1

Blue

Question 2

What is an electrolyte?

Answer 2

An ionic compound which is molten or dissolved in water

Question 3

What is electrolysis?

Answer 3

The splitting up of electrolytes using electrical energy

Question 4

Write the half equation for the reaction occurring at the cathode when CuSO4 is electrolysed

Answer 4

Cu^2+(aq) + 2e- → Cu(s)

Question 5

Write a half equation for the formation of oxygen from OH- ions

Answer 5

4OH-(aq)→2H2O(l) + O2(g) + 4e-

Question 6

At which electrode does oxidation?

Answer 6

Positive electrode

Question 7

To which electrode do positive ions move towards?

Answer 7

Negative electrode (cathode)

Question 8

What forms at the cathode and the anode in electrolysis?

Answer 8

Cathode - metals or hydrogen Anode - non-metals

Question 9

What are the products of electrolysis of copper sulfate when using inert electrodes?

Answer 9

Copper at negative electrode Oxygen at positive electrode

Question 10

How do you set up an electrochemical cell?

Answer 10

Place positive and negative electrodes in a beaker containing a molten or dissolved ionic compound. Connect both electrodes to a power supply with wires.

Question 11

When carrying out the electrolysis of CuSO4, what safety precautions should be taken?

Answer 11

Wear gloves and safety goggles (copper sulfate causes skin and eye irritation)

Keep propanone (for drying the electrodes) away from flames and use in fume cupboard

Question 12

What observations could you make when CuSO4 is electrolysed using inert electrodes?

Answer 12

Cathode - copper deposit (brown/pink solid)

Anode - bubbles of O2 gas Solution - blue colour fades

Question 13

What does inert mean?

Answer 13

Unreactive

Question 14

How would you test the gas produced at the anode for electrolysis of CuSO4?

Answer 14

If the gas is oxygen, it will relight a glowing splint

Question 15

You are using copper electrodes for the electrolysis of CuSO4. Over time, what happens to the anode? Why?

Answer 15

Mass will decrease. Cu(s) in the electrode are oxidised to Cu2+(aq)

Question 16

You are using copper electrodes for the electrolysis of CuSO4. How are the change in masses of the electrodes linked?

Answer 16

The mass lost from the anode should be the same as the mass gained by the cathode

Question 17

You are using copper electrodes for the electrolysis of CuSO4. What is the relationship between the mass gained by the cathode and the current used?

Answer 17

The mass gained by the cathode is directly proportional to the current used (for a given time)

Question 18

Why must you clean the copper electrodes with emery paper before use?

Answer 18

To remove any copper oxide which may have formed

Question 19

Why should you dry the copper electrodes at the end of the electrolysis of CuSO4?

Answer 19

So the change in mass is only caused by the gain/ loss of copper atoms