Core practical - electrolysis of copper sulfate solution. p2

Question 1

why are copper electrodes described as non-inert?

Answer 1

because they take part in the reactions

Question 2

describe what happens at the positive and negative electrodes: (2)

Answer 2

at the positive electrode, copper atoms lose electrons and form copper ions, Cu2+

at the negative electrode, copper ions gain electrons and form copper atoms

Question 3

method: (8)

Answer 3

1- Pour some copper sulfate solution into a beaker.
2- Measure and record the mass of a piece of copper foil. Attach it to the negative terminal of a dc supply, and dip the copper foil into the copper sulfate solution.
3- Repeat step 2 with another piece of copper foil, but this time attach it to the positive terminal.
4- Make sure the electrodes do not touch each other, then turn on the power supply. Adjust the power supply to achieve a constant current as directed by your teacher.
5- After 20 minutes, turn off the dc supply.
6- Carefully remove one of the electrodes. Gently wash it with distilled water, then dip it into propanone. Lift the electrode out and allow all the liquid to evaporate. Do not wipe the electrodes clean. Measure and record the mass of the electrode.
7- Repeat step 6 with the other electrode. Make sure you know which is which.
8- Repeat the experiment with fresh electrodes and different currents.

Question 4

what should you do after this practical (analysis)?

Answer 4

calculate the change in mass of each electrode

Question 5

Draw conclusions about what is happening during the electrolysis: (2)

Answer 5

• The gain in mass by the negative electrode is the same as the loss in mass by the positive electrode.
• So the copper deposited on the negative electrode must be the same copper ions that are lost from the positive electrode

Question 6

harms and precautions of using Copper sulfate solution and Propanone: (4)

Answer 6

Copper sulfate solution:

harm: Causes skin and serious eye irritation
precaution: Wear gloves and eye protection

Propanone:

harm: Highly flammable liquid and vapour - may cause drowsiness or dizziness
precaution: Keep away from naked flames - use it in a fume cupboard