4. Chemical Changes (required practical 3 - electrolysis in aqueous solutions)

Question 1

What is the practical?

Answer 1

Investigating what happens when aqueous solutions undergo electrolysis

Question 2

What are the two different solutions for this practical?

Answer 2

• copper (II) chloride
• sodium chloride

Question 3

What are the steps for the electrolysis of aqueous copper (II) chloride solution?

Answer 3

1. Firstly, pour approximately 50cm3 of copper (II) chloride solution into a beaker
2. Place a plastic petri dish over the beaker, the petri dish should have two holes
3. Then insert a carbon graphite rod into each hole, which are the electrodes
4. Attach crocodile leads to the rods and then connect the rods to the terminals of a low voltage power supply. Select 4v on the power supply and switch it on.
5. The cathode starts being coated with copper
6. Bubbles of chlorine gas are formed at the anode

Question 4

What are carbon-graphite electrodes inert?

Answer 4

because carbon graphite is unreactive, so the electrodes wont react

Question 5

Why musn’t the two electrodes touch each other?

Answer 5

As that would produce a short circuit

Question 6

What does aqueous mean?

Answer 6

dissolved in water

Question 7

What do the ions discharged when an aqueous solution is electrolysed depend on?

Answer 7

The relative reactivity of the elements involved

Question 8

What is produced at the anode during the electrolysis of an aqueous solution?

Answer 8

Oxygen is produced unless the solution contains a halide ion, in which the halide ion would be produced

Question 9

What additional ions are present in an aqueous solution?

Answer 9

• OH-
• H+

Question 10

Why is hydrogen produced rather than the more reactive elements than hydrogen?

Answer 10

More reactive ions want to stay within the solution

Question 11

What are the steps for the electrolysis of aqueous sodium chloride solution?

Answer 11

1. Place approximately 50cm3 of sodium chloride solution into a beaker
2. Place a plastic petri dish over the beaker, the petri dish should have two holes
3. Then insert a carbon graphite rod into each hole, which are the electrodes
4. Turn on the low voltage power supply and look at the two electrodes
5. At the anode, chlorine gas is produced
   At the cathode, there are gas bubbles of hydrogen
6. To test the gas is hydrogen, use the squeaky pop test