Electrolysis

Question 1

What is electrolysis?

Answer 1

Electrolysis is the breaking down of a compound using electricity. It involves passing a current through an electrolyte to cause a chemical change.

Question 2

What is an electrolyte?

Answer 2

A liquid or molten substance that conducts electricity, containing ions.

Question 3

What are electrodes?

Answer 3

Electrodes are solid conductors (usually graphite or metal) placed in the electrolyte.
• Anode = positive electrode
• Cathode = negative electrode

Question 4

What happens at the electrodes during electrolysis?

Answer 4

Cathode (−): Positive ions gain electrons (reduction)
• Anode (+): Negative ions lose electrons (oxidation)

Question 5

What does OIL RIG mean in electrolysis?

Answer 5

OIL = Oxidation Is Loss (of electrons)
• RIG = Reduction Is Gain (of electrons)

Question 6

What is produced at each electrode during the electrolysis of molten ionic compounds (e.g. lead bromide)?

Answer 6

Cathode: metal (e.g. lead)
• Anode: non-metal (e.g. bromine)

Question 7

How does water affect what is produced in electrolysis of solutions?

Answer 7

A: Water introduces H⁺ and OH⁻ ions. These compete with the ions from the salt.

Question 8

What are the general rules for aqueous electrolysis?

Answer 8

At cathode: If metal is more reactive than hydrogen → hydrogen gas is produced.
• At anode: If solution contains halide ions (Cl⁻, Br⁻, I⁻) → halogen gas.
If not → oxygen gas (from OH⁻) is produced.

Question 9

What are the products of electrolysing sodium chloride solution (NaCl)?

Answer 9

Cathode: Hydrogen gas (H₂)
• Anode: Chlorine gas (Cl₂)
• Left in solution: Sodium hydroxide (NaOH)

Question 10

What is one major use of electrolysis?

Answer 10

Extracting reactive metals, like aluminium, from their ores.

Question 11

What is a half equation for sodium ions at the cathode?

Answer 11

A: Na⁺ + e⁻ → Na (reduction)