Electrolysis

Question 1

why do covalent compounds not conduct electricity?

Answer 1

They have no delocalized electrons that can carry charge

Question 2

why can ionic compounds conduct electricity when molten or in an aqueous solution

Answer 2

because then there are delocalized electrons that can carry charge

Question 3

positive ions are called what

Answer 3

cations

Question 4

negative ions are called what

Answer 4

anions

Question 5

describe the experiment to investigate the electrolysis of lead(II) bromide

Answer 5

• Power supply at 12V, separate rods and lower into lead bromide powder
• Roaring Bunsen flame to melt powder in crucible
• Adjust current to 1.5A
• Brown colour of bromine seen, moist universal indicator paper held in vapour, it goes to red/slightly bleached
• Maintain for 15 minutes, then pour molten lead bromide into second crucible, keeping molten lead in the first
• Cooled lead can be marked with a fingernail

Question 6

In the electrolysis of sodium carbonate solution, what are the products formed at each electrode?

Answer 6

Cathode - Hydrogen
Anode - Oxygen

Question 7

Why do you think the anode gets smaller over time in the electrolysis of potassium nitrate?

Answer 7

Oxygen reacts with the carbon electrode forming CO2

Question 8

3. Write half-equations for the reactions occurring at each electrode in the electrolysis of potassium chloride solution. Label which is oxidation and which is reduction.

Answer 8

2H+ + 2e- –> H2 - reduction
2Cl- –> Cl2 + 2e- - oxidation

Question 9

Write the half-equations for electrolysis of sodium chloride solution

Answer 9

2Cl- –> Cl2 + 2e-
2H+ + 2e- –> H2

Question 10

Describe the experiment of the electrolysis of sodium chloride

Answer 10

• Two carbon electrodes connected to a battery in two upside down glass tubes surrounded by concentration sodium chloride solution within a beaker with a rubber bung
• add 4 drops of universal indicator and stir
• once some gas collected stop/switch off
• use damp blue litmus to test gas at anode

Question 11

describe the experiment of the electrolysis of dilute sulphuric acid

Answer 11

• setup hoffman voltameter with power supply and sulphuric acid
• glowing splint to test gas at anode
• lit splint to test the gas at cathode

Question 12

what are the five parts of the hoffman voltameter

Answer 12

bulb, stopcock, central tube, anode, cathode

Question 13

describe the experiment of the electrolysis of copper(II) sulphate

Answer 13

• beaker with copper(II) sulphate solution
• two carbon (graphite) electrodes connected to 6V DC power supply

Question 14

Write the ionic half equations for the electrolysis of sodium chloride

Answer 14

2Na+ + 2e- –> 2Na
2Cl- –> Cl2 + 2e-

Question 15

Write the ionic half equations for the electrolysis of sulphuric acid

Answer 15

2H+ + 2e- → H2
4OH- → O2 + 2H2O + 4e-