Answer to Question #93904 in General Chemistry for Kylie

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.