定义Definition
次氯酸 HClO 是氯的含氧酸，氯的氧化数为 +1。它是很弱的酸（pKa 约 7.5），但氧化性很强，能漂白和杀菌。HClO 只存在于溶液中，不稳定，见光分解。氯气溶于水时生成次氯酸。
Hypochlorous acid, HClO, is an oxoacid of chlorine in the +1 oxidation state. It is a very weak acid (pKa about 7.5) but a strong oxidising agent that bleaches and kills microbes. It exists only in solution, is unstable and decomposes in light. It forms when chlorine dissolves in water.
氯水中的反应Chlorine water
Cl₂ + H₂O ⇌ HCl + HClO，氯发生歧化。新制氯水能使湿润的有色布条褪色，起漂白作用的是 HClO；久置的氯水因 HClO 分解（2HClO → 2HCl + O₂）而失去漂白性。
Cl₂ + H₂O ⇌ HCl + HClO, a disproportionation of chlorine. Fresh chlorine water bleaches damp coloured cloth, the bleaching agent being HClO; chlorine water left standing loses this power because HClO decomposes, 2HClO → 2HCl + O₂.
水的消毒Water treatment
自来水加氯消毒的有效成分是 HClO。它在弱酸性时含量较高，pH 升高时转化为杀菌能力较弱的 ClO⁻，所以消毒效果与水的 pH 有关。
HClO is the active disinfectant in chlorinated water. It predominates in slightly acidic water; as pH rises it turns into ClO⁻, a weaker germicide, so disinfection depends on pH.
化学性质Chemical properties
见光分解：2HClO → 2HCl + O₂
Decomposes in light: 2HClO → 2HCl + O₂
与碱反应：HClO + NaOH → NaClO + H₂O
With alkali: HClO + NaOH → NaClO + H₂O