Redox & Disproportionation (Edexcel A Level Chemistry): Revision Note

Balancing disproportionation reactions

Balance the disproportionation reaction which takes place when chlorine is added to hot concentrated aqueous sodium hydroxide. The products are Cl^- and ClO₃^- ions and water

Answer

Step 1: Write the unbalanced equation and identify the atoms that change in oxidation number:

Step 2: Deduce the oxidation number changes:

Step 3: Balance the oxidation number changes:

Step 4: Balance the charges

Step 5: Balance the atoms

Oxidation and reduction

In each of the following equations, state which reactant has been oxidised and which has been reduced.

1. Na⁺+ Cl^- →  NaCl

2. Mg + Fe²⁺  →  Mg²⁺ + Fe

3. CO + Ag₂O  →  2Ag + CO₂

Answer 1:

• Oxidised: Cl^- as the oxidation state has increased by 1

  • Reduced: Na⁺ as the oxidation state has decreased by 1

Answer 2:

• Oxidised: Mg as the oxidation state has increased by 2

  • Reduced: Fe²⁺ as the oxidation state has decreased by 2

Answer 3:

• Oxidised: C as it has gained oxygen

  • Reduced: Ag as it has lost oxygen