6.4 Electrolysis of aqueous solutions + RP

Question 1

Investigating the electrolysis of solutions required practical:

Answer 1

1. Half fill a beaker with the solution to be electrolysed
2. Submerge the ends of the two electrodes and using the crocodile clips and wires connect them to the low voltage power supply
3. Make sure the electrodes are not touchhing
4. Turn on the power supply. If you see bubbles, a gas is being made. Turn it off
5. Fill three ignition tubes with the solution, hold them upright so that opening is still under liquid level and over the electrode that is making gas
6. Turn on the power and when the ignition tube is full of gas seal it with a bung
7. Repeat steps 5-6 until three ignition tubes have been collected from each electrode that is making a gas
8. Turn off the power supply
9. Test each gas for hydrogen, oxygen, chlorine

Question 2

Explain why it is important to wear nitrile gloves if you are collecting the gas by displacement

Answer 2

Solutions and gases may be harmful to your skin as the could irritate it.

Question 3

State the equation for the electrolysis of brine

Answer 3

Sodium chloride solution —> (electrolysis) hydrogen gas, chlorine gas, sodium hydroxide solution

Question 4

What is produced at the anode in the electrolysis of brine

Answer 4

• negative chlorine ions attracted to positive electrode
• they lose one electron (oxidation)
• Chlorine atoms bond together in pairs and are given off as a chlorine gas

Question 5

What is produced at the cathode in the electrolysis of brine

Answer 5

• positive hydrogen ions are attracted to the negative electrode
• sodium ions are also attracted to the same electrode
• it is less reactive so hydrogen ions are discharged and sodium ions stay in solution
• hydrogen ions gain one electron (reduced)
• hydrogen atoms formed bond together in pairs and give off hydrogen gas

Question 6

What is the half equation for the electrolysis of brine at the anode?

Answer 6

2Cl-(aq) —> Cl2(g) + 2e-

Question 7

What is the half equation for the electrolysis of brine at the cathode?

Answer 7

2H+ (aq) + 2e- —> H2(g)

Question 8

How do you test for hydrogen, oxygen and chorine?

Answer 8

Hydrogen: a lit splint will make a ‘pop’ sound
Oxygen: a glowing splint will relight
Chlorine: damp blue litmus paper will turn red and then be bleached