Experiment 1C (The Effects of Type of Electrode on the Selection of Ions to be Discharged) :
Aim: To study the effects of the type of electrode used on the selective discharge of ions at the electrodes.
Problem statement: Does the type of electrode used affect the selective discharge of ions at the electrodes?
Hypothesis: Construct a hypothesis that relate the type of electrode used with the products formed at the anode.
Variables: State all variables.
Material: 0.5 mol dm−3 of copper(II) sulphate, CuSO4 solution.
Apparatus: Beaker, battery, carbon electrode, copper electrode, connecting wires with crocodile clips, switch, ammeter, test tube, wooden splinter, electronic scale and sandpaper.
Procedure:
Using the apparatus and material provided, plan an experiment to investigate the effects of the type of electrode used on the products formed at the anode.
Results:
Record all observations in a table.
Discussion:
1. Name the products formed during the electrolysis of copper(II) sulphate, CuSO4 using electrode:
(a) carbon.
(b) copper.
2. Write the half equations to show the formations of products at the anode for the electrolysis of copper(II) sulphate, CuSO4 solution using electrode:
(a) carbon.
(b) copper.
3. What can be observed of the colour of copper(II) sulphate, CuSO4 solution when electrolysis is carried out using electrode:
(a) carbon.
(b) copper.
Explain your answer.
Answer:
Hypothesis:
When carbon electrodes are used, colourless gas bubbles are released at the anode, while when copper electrodes are used, the copper at the anode becomes thinner.
Variables:
(a) Manipulated variable : Carbon electrode and copper electrode
(b) Responding variable : Observation at anode
(c) Fixed variable : Copper(II) sulphate solution
Prosedure:
1. Pour 0.5 mol dm−3 of copper(II) sulphate solution, CuSO4 into a beaker until half full.
2. Connect the carbon electrodes to the switch and batteries using the connecting wires.
3. Dip the carbon electrodes into the copper(II) sulphate solution to complete the curcuit.
4. Observe and record the changes that occur at the anode and the cathode in a table.
5. Repeat steps 1 to 4 using copper electrodes to replace carbon electrodes.
Result:
1. (a)
Cathode : Copper
Anode : Oxygen
1. (b)
Cathode : Copper
Anode : Copper(II) ion.
2. (a) Anode : 4OH− → O2 + 2H2O + 4e−
2. (b) Anode : Cu → Cu2+ + 2e−
3. (a)
– The blue colour of copper(II) sulphate solution becomes paler.
– The concentration of Cu2+ ions decreases.
– Cu2+ ions are discharged to form copper atoms at the cathode.
3. (b)
– The blue colour of copper (II) sulphate solution remains unchanged.
– The concentration of Cu2+ ions remains unchanged.
– The discharged rate of Cu2+ ions to form copper atoms at the cathode is the same as the ionisation rate of copper atoms to form Cu2+ ions at the anode.
Aim: To study the effects of the type of electrode used on the selective discharge of ions at the electrodes.
Problem statement: Does the type of electrode used affect the selective discharge of ions at the electrodes?
Hypothesis: Construct a hypothesis that relate the type of electrode used with the products formed at the anode.
Variables: State all variables.
Material: 0.5 mol dm−3 of copper(II) sulphate, CuSO4 solution.
Apparatus: Beaker, battery, carbon electrode, copper electrode, connecting wires with crocodile clips, switch, ammeter, test tube, wooden splinter, electronic scale and sandpaper.
Procedure:
Using the apparatus and material provided, plan an experiment to investigate the effects of the type of electrode used on the products formed at the anode.
Results:
Record all observations in a table.
Discussion:
1. Name the products formed during the electrolysis of copper(II) sulphate, CuSO4 using electrode:
(a) carbon.
(b) copper.
2. Write the half equations to show the formations of products at the anode for the electrolysis of copper(II) sulphate, CuSO4 solution using electrode:
(a) carbon.
(b) copper.
3. What can be observed of the colour of copper(II) sulphate, CuSO4 solution when electrolysis is carried out using electrode:
(a) carbon.
(b) copper.
Explain your answer.
Answer:
Hypothesis:
When carbon electrodes are used, colourless gas bubbles are released at the anode, while when copper electrodes are used, the copper at the anode becomes thinner.
Variables:
(a) Manipulated variable : Carbon electrode and copper electrode
(b) Responding variable : Observation at anode
(c) Fixed variable : Copper(II) sulphate solution
Prosedure:
1. Pour 0.5 mol dm−3 of copper(II) sulphate solution, CuSO4 into a beaker until half full.
2. Connect the carbon electrodes to the switch and batteries using the connecting wires.
3. Dip the carbon electrodes into the copper(II) sulphate solution to complete the curcuit.
4. Observe and record the changes that occur at the anode and the cathode in a table.
5. Repeat steps 1 to 4 using copper electrodes to replace carbon electrodes.
Result:
1. (a)
Cathode : Copper
Anode : Oxygen
1. (b)
Cathode : Copper
Anode : Copper(II) ion.
2. (a) Anode : 4OH− → O2 + 2H2O + 4e−
2. (b) Anode : Cu → Cu2+ + 2e−
3. (a)
– The blue colour of copper(II) sulphate solution becomes paler.
– The concentration of Cu2+ ions decreases.
– Cu2+ ions are discharged to form copper atoms at the cathode.
3. (b)
– The blue colour of copper (II) sulphate solution remains unchanged.
– The concentration of Cu2+ ions remains unchanged.
– The discharged rate of Cu2+ ions to form copper atoms at the cathode is the same as the ionisation rate of copper atoms to form Cu2+ ions at the anode.