Exercise 4 | Oxidation-Reduction Reactions

Under acidic conditions the bromate ion is reduced to bromide ion.

Write the balanced half-reaction for this process.

What would be the balanced half-reaction under basic conditions?

Bromate ion: BrO3-

Bromide ion: Br-

Unbalanced reaction: BrO3- → Br-

 

1) Balance atoms (other than O and H): Br is already balanced

2) Balance O atoms by adding H2O molecules: BrO3- → Br- + 3 H2O

3) Balance H atoms by adding H+ ions: BrO3- + 6 H+ → Br- + 3 H2O

4) Balance charge by adding electrons: BrO3- + 6 H+ + 6 e- → Br- + 3 H2O

Half-reaction under acidic conditions: BrO3- + 6 H+ + 6 e- → Br- + 3 H2O

 

Under basic conditions: add HO- ions to react with all H+ ions: HO- + H+ → H2O

BrO3- + 6 H+ + 6 e- + 6 HO- → Br- + 3 H2O + 6 HO-

BrO3- + 6 H2O + 6 e- → Br- + 3 H2O + 6 HO-

BrO3- + 3 H2O + 6 e- → Br- + 6 HO-

Half-reaction under basic conditions: BrO3- + 3 H2O + 6 e- → Br- + 6 HO-