Core Practical: Electrolysis of Copper(II)Sulfate Flashcards

All 6 cards in this deck

True or false? When copper sulfate solution is electrolysed with copper electrodes, the anode loses mass and the cathode gains mass.

True. Copper atoms dissolve from the anode as ions and copper is deposited on the cathode.

What are the half equations at the anode and cathode when copper sulfate solution is electrolysed with copper electrodes?

Anode: $\mathrm{Cu \rightarrow Cu^{2+} + 2e^-}$
Cathode: $\mathrm{Cu^{2+} + 2e^- \rightarrow Cu}$

Why does the blue colour of copper sulfate solution stay the same when it is electrolysed with copper electrodes?

$\mathrm{Cu^{2+}}$ ions enter the solution at the anode at the same rate as they leave at the cathode, so the concentration is unchanged.

What are the steps to measure the mass change of an electrode in the electrolysis of copper sulfate solution?

e.g. a copper cathode electrolysed for 10 minutes

1. Clean with emery paper to remove surface oxide/grease, dry and weigh
2. Electrolyse at a set current for 10 minutes
3. Rinse, dry and reweigh: mass change = final mass − initial mass

How is impure copper purified by electrolysis?

Impure copper is the anode and pure copper the cathode in copper sulfate solution; copper dissolves from the anode and is deposited as pure copper on the cathode.

How does the mass of copper deposited on the cathode depend on the current and the time?

It is directly proportional to both.

e.g. three times the current for the same time deposits three times the mass.