Laboratory Activity 1F (Textbook) – Chemistry Form 5 Chapter 1 (Redox Equilibrium)

Laboratory Activity 1F (Electrolysis of an Aqueous Solution Using Carbon Electrodes):
Aim: To study the electrolysis of the aqueous solution of copper(II) sulphate, CuSO₄ and dilute sulphuric acid, H₂SO₄ with carbon electrodes.

Materials: 0.1 mol dm⁻³ of copper(II) sulphate, CuSO₄ solution and 0.1 mol dm⁻³ of sulphuric acid, H₂SO₄

Apparatus: Electrolytic cell, battery, carbon electrodes, connecting wire with crocodile clip, switch, ammeter, test tubes and wooden splinter.

Procedure:
1. Pour the 0.1 mol dm⁻³ of copper(II) sulphate, CuSO₄ solution into the electrolytic cell until half full.

2. Fill two test tubes with 0.1 mol dm⁻³ of copper(II) sulphate, CuSO₄ solution until full and invert them on top of the carbon electrodes in the electrolytic cell.

3. Connect the carbon electrodes to the switch, ammeter and battery with the connecting wires to complete the circuit as shown in Figure 1.27.



4. Turn the switch on for a few minutes.

5. Observe and record any changes at the anode and cathode.

6. Carry out the confirmatory tests on the collected gases.
(a) Insert a glowing wooden splinter into the test tube at the anode.
(b) Place a burning wooden splinter into the test tube at the cathode.

7. Repeat steps 1 to 6 using 0.1 mol dm⁻³ of sulphuric acid, H₂SO₄.

8. Record your observations.

Results:
Record all observations in the table below.



Discussion:
1. State the ions present in the aqueous solution of:
(a) Copper(II) sulphate, CuSO₄ solution.
(b) Sulphuric acid, H₂SO₄.

2. For each of the copper(II) sulphate, CuSO₄ solution and sulphuric acid, H₂SO₄:

(a) name the ions that move to the cathode and anode during electrolysis.

(b) identify the ions discharged at the cathode and anode. Give a reason for your answer.

(c) name the products formed at the cathode and anode.

(d) write the half equations of the reactions that take place at the cathode and anode.

(e) explain how the products at the cathode and anode are formed.

(f) write the overall ionic equation that represents electrolysis.


Answer:
Result:


Discussion:
1. (a) $$\mathrm{Cu}^{2+} \text { ion, } \mathrm{SO}_4{ }^{2-} \text { ion, } \mathrm{H}^{+} \text {ion, } \mathrm{OH}^{-} \text {ion }$$

1. (b) $$\mathrm{H}^{+} \text {ion, } \mathrm{SO}_4^{2-} \text { ion, } \mathrm{OH}^{-} \text {ion }$$

2.
Copper (II) sulphate solution


(f) $$2 \mathrm{Cu}^{2+}+4 \mathrm{OH}^{-} \rightarrow 2 \mathrm{Cu}+\mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O}$$


Sulphuric acid


(f) $$4 \mathrm{H}^{+}+4 \mathrm{OH}^{-} \rightarrow 2 \mathrm{H}_2+\mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O}$$