Electrolysis

Question 1

Electrolysis definition

Answer 1

the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current

Question 2

What is the anode in an electrolytic cell?

Answer 2

positive electrode

Question 3

What is the cathode in an electrolytic cell?

Answer 3

negative electrode

Question 4

Electrolyte definition

Answer 4

The molten or aqueous substance that undergoes electrolysis

Question 5

What are the products and observations during electrolysis of molten lead(II) bromide?

Answer 5

•Cathode: Lead metal forms (grey/silver molten droplets)
•Anode: Bromine gas forms (brown/orange fumes)

Question 6

What are the products and observations during electrolysis of concentrated aqueous sodium chloride (brine)?

Answer 6

•Cathode: Hydrogen gas (bubbles)
•Anode: Chlorine gas (green gas with bleaching smell)
•Solution left: Sodium hydroxide

Question 7

What are the products and observations during electrolysis of dilute sulfuric acid with inert electrodes?

Answer 7

•Cathode: Hydrogen gas (bubbles)
•Anode: Oxygen gas (bubbles)
•Hydrogen is produced in twice the volume of oxygen

Question 8

How is charge transferred during electrolysis in the external circuit?

Answer 8

By the movement of electrons

Question 9

How is charge transferred at the electrodes during electrolysis?

Answer 9

By the loss or gain of electrons

Question 10

How is charge transferred in the electrolyte during electrolysis?

Answer 10

By the movement of ions

Question 11

What happens during electrolysis of aqueous copper(II) sulfate with carbon/graphite electrodes?

Answer 11

•Cathode: Copper metal forms (reddish-brown deposit)
•Anode: Oxygen gas forms (bubbles)
•Observation: Blue colour of solution fades

Question 12

What happens during electrolysis of aqueous copper(II) sulfate with copper electrodes?

Answer 12

•Cathode: Copper is deposited.
•Anode: Copper dissolves into solution.
•Observation: Blue colour remains the same.

Question 13

What substances are formed at each electrode during electrolysis?

Answer 13

•Cathode: Metals or hydrogen
•Anode: Non-metals (except hydrogen)

Question 14

How can you predict the products of electrolysis of a binary compound in the molten state?

Answer 14

•Metal ion → metal at the cathode
•Non-metal ion → non-metal at the anode

Question 15

What is a hydrogen–oxygen fuel cell?

Answer 15

A cell that uses hydrogen and oxygen to produce electricity, with water as the only chemical product

Question 16

advantages of hydrogen–oxygen fuel cells compared with petrol engines? (3)

Answer 16

•Only produces water (no CO₂ pollution)
•More energy efficient
•Less air pollution

Question 17

disadvantages of hydrogen–oxygen fuel cells compared with petrol engines? (3)

Answer 17

•Hydrogen storage is difficult and dangerous
•Hydrogen is expensive to produce
•Requires special infrastructure

Question 18

What happens at the cathode during electrolysis?

Answer 18

Reduction - ions gain electrons

Question 19

What happens at the anode during electrolysis?

Answer 19

Oxidation - ions lose electrons

Question 20

half-equation for hydrogen forming at the cathode

Answer 20

2H^+ + 2e^- —> H_2

Question 21

half-equation for oxygen forming at the anode

Answer 21

4OH^- —> O2 + 2H_2O + 4e^-

Question 22

half-equation for copper forming at the cathode

Answer 22

Cu^2+ + 2e^- —> Cu

Question 23

half-equation for chlorine and bromine forming at the anode

Answer 23

2Cl^- —> Cl_2 + 2e^-

2Br^- —> Br_2 + 2e^-

Question 24

What type of ions move to the cathode?

Answer 24

Positive ions (cations)

Question 25

What type of ions move to the anode?

Answer 25

Negative ions (anions)

Question 26

Halide rule (at anode)

Answer 26

If halide ions are present in solution it will react and make a halogen gas, if not OH^-(aq) reacts and O2 is formed - Cl^-(aq), Br^-(aq), F^-(aq) —> Cl2(g)

Question 27

Jewellery metal rule (at cathode)

Answer 27

If a jewellery metal is present in solution then that metal will react and will form, if not then H^+(aq) reacts and H2(g) is formed