Question

Consider the reaction of sodium hypochlorite with iodine.

Why is hydrochloric acid added to the dilute bleach and iodine in the conical flask?

Answer 1

Hydrochloric acid is added to the dilute bleach and iodine, because the hypochlorite in the bleach solution is reacted with iodide ion under acidic conditions with the formation of iodine:

reduction of chlorine: ClO^-(aq) + 2H⁺(aq) + 2e → Cl^-(aq) + H₂O

oxidation of iodine: 2I^-(aq) - 2e → I₂(aq)

redox reaction: NaClO(aq) + 2HCl(aq) + 2NaI(aq) → 3NaCl(aq) + H₂O(l) + I₂(aq)

We can determine the amount in moles of I₂ in the solution by titration with standardized sodium thiosulfate.