Oxochlorate(I) acid is used as a bleaching agent because it is

Analyze the question Oxochlorate(I) acid is HOCl (hypochlorous acid). The question asks why it works as a bleaching agent.

Explain the concept Bleaching by chlorine-based compounds is an oxidation process. Coloured substances (dyes and stains) contain chromophores, which are groups that absorb visible light. An oxidizing agent breaks down or changes these chromophores, so the substance loses its colour.

Step-by-step solution

1. HOCl contains chlorine in the +1 oxidation state, which is the meaning of "(I)" in oxochlorate(I).
2. Chlorine is very stable as chloride (Cl⁻, oxidation state −1), so HOCl readily gains electrons: HOCl + H⁺ + 2e⁻ → Cl⁻ + H₂O
3. Because it gains electrons, HOCl is reduced, and so it is an oxidizing agent.
4. In bleaching, HOCl releases nascent (atomic) oxygen: HOCl → HCl + [O] The [O] oxidizes the coloured dye to a colourless compound: Dye (coloured) + [O] → Oxidized dye (colourless)

Checking the options

• A. Weak acid: HOCl is a weak acid, but acid strength is not what causes bleaching.
• B. Reducing agent: wrong, because Cl(+1) is reduced, not oxidized.
• C. Oxidizing agent: correct, because bleaching works by oxidation.
• D. Strong acid: wrong, because HOCl is weak, and acid strength is irrelevant to bleaching anyway.

Exam tip Bleaching agents such as chlorine, HOCl, NaOCl (household bleach) and H₂O₂ are generally oxidizing agents. The exception is SO₂, which bleaches by reduction. So "bleach = oxidize" works for most WASSCE questions.