Electrolysis (U2)

Question 1

What is electrolysis?

Answer 1

Electrolysis is the breakdown of aqueous or molten ionic compounds by electricity to give new elements.

Question 2

What are the conditions required for electrolysis?

Answer 2

• The substance must be a good conductor of electricity (metals, graphite, aqueous/molten ionic compounds).
• Graphite is used as it is made of carbon, which is uncharged and does not change its structure.

Stainless steel does not work because it is a bad conductor.
Metals cannot be electrolyzed as they are already in their simplest form.

Question 3

What are the key components of an electrolysis setup?

Answer 3

• Power Supply: Provides electricity (e.g., battery).
• Wires: Conduct electricity between components.
• Electrodes: Made of graphite or platinum:
• Anode (positive terminal): Where non-metals go.
• Cathode (negative terminal): Where metals go.
• Electrolyte: The ionic compound to be electrolyzed

Question 4

How do ions move during electrolysis?

Answer 4

Unlike poles attract:
* Metal ions (cations, +) go to the cathode (-).
* Non-metal ions (anions, -) go to the anode (+).

Question 5

What happens when molten ionic compounds undergo electrolysis?

Answer 5

Example 1: CuS (Copper Sulfide)
* Cathode: Cu²⁺ + 2e⁻ → Cu
* Anode: S²⁻ → S + 2e⁻
Example 2: PbBr₂ (Lead Bromide)
* Cathode: Pb²⁺ + 2e⁻ → Pb
* Anode: 2Br⁻ → Br₂ + 2e⁻

Question 6

What are the rules for determining products in aqueous electrolysis?

Answer 6

Cathode Rule: The least reactive positive ion reacts.
* If the metal is below H⁺ in the reactivity series, the metal forms.
* If the metal is above H⁺, H⁺ reacts instead.

Anode Rule:
* If the solution is concentrated and contains a halide, the halide ion reacts.
* Otherwise, OH⁻ reacts.

Question 7

What happens during the electrolysis of CuSO₄ (Copper Sulfate)?

Answer 7

• Ions involved: Cu²⁺, SO₄²⁻, H⁺, OH⁻
• Cathode Reaction: Cu²⁺ + 2e⁻ → Cu
• Anode Reaction: 4OH⁻ → 2H₂O + O₂ + 4e⁻