ES 3- Manufacturing Chlorine

Question 1

Define electrolysis

Answer 1

Breaking down of a compound using electricity

Question 2

Is the anode positively or negatively charged?

Answer 2

Positively charged

Question 3

In electrolysis, cations migrate to…

Answer 3

Cathode

Question 4

In electrolysis, anions migrate to…

Answer 4

Anode

Question 5

Which line in symbol for cell/battery in electrolysis represents the negative terminal?

Answer 5

Shorter line

Question 6

Define electrolyte

Answer 6

• molten or aqueous salt that has ions that are free to move and carry a current

Question 7

Does oxidation or reduction occur at anode?

Answer 7

Oxidation, negative ions lose electrons

Question 8

In electrolysis of molten lead bromide, what will occur at anode?

Answer 8

2Br-(l)     Br2(g) + 2e-
Bromide gas (orange) formed

Question 9

Why electrolysis in an aqueous solution different to in aqueous solution?

Answer 9

• water can be reduced and oxidised

Question 10

Predict products of electrolysis of molten salt on each electrode

Answer 10

At cathode: metal

At anode: non-metal, apart from hydrogen

Question 11

Give equation for oxidation of water at anode

Answer 11

2H2O(l) O2(g) + 4H+(aq) + 4e-

Question 12

In electrolysis of an aqueous solution, in which circumstances would water be oxidised at anode instead of other negative ions?

Answer 12

• sulfates and nitrates are less easily oxidised than water, oxygen gas would be formed at anode

Question 13

What is formed at anode in aqueous solutions, if halide ions are present?

Answer 13

• halogen, halides more easily oxidised than water

Question 14

What occurs at anode if hydroxide ions are present in aqueous solution?

Answer 14

Hydroxide ions are oxidised, forming oxygen

Question 15

Does oxidation or reduction occur at cathode?

Answer 15

Reduction, positive ions gain electrons

Question 16

In electrolysis of molten lead bromide, what occurs at cathode?

Answer 16

Pb2+(l) + 2e- Pb(s)

- lead metal formed

Question 17

Write equation of reduction of water

Answer 17

2H20(l) + 2e- 2OH-(aq) + H2(g)

Hydrogen gas produced

Question 18

In what circumstances would water be reduced at cathode instance of metal ions?

Answer 18

If solution contains ions from group 1, 2 or aluminium

- are very reactive and will stay as ions

Question 19

What occurs at cathode if solution is acid?

Answer 19

H+ ions re reduced forming H2 gas

Question 20

Define inert

Answer 20

Chemically inactive

Question 21

What occurs in electrolysis of copper sulphate solution with a copper anode?

Answer 21

• at anode, copper atoms are oxidised forming copper ions, so anode reduces in mass
• at cathode, copper ions are reduced forming copper atoms, so copper is deposited and cathode is plated

Question 22

In electrolysis of copper sulphate solution and copper anode, what happens to the concentration of the solution?

Answer 22

• remain constant, as copper metal is turned to ions at anode, and ions are turned to metal at cathode