# Chlorination of Water

Does passing chlorine gas through water form hydrochloric acid or bleach? Also, will a mixture of hydrogen and chlorine gas from electrolysis of brine do the same?

• Common house hold bleach is actually basic, as it consists of a solution of sodium hypochlorite, among other things. – Dissenter Aug 18 '14 at 2:43
• @Dissenter I think he's asking if it will form one or the other, not implying that hydrochloric acid is also called bleach. That's how I read it anyways. – canadianer Aug 18 '14 at 3:01
• Cl2 + H2O = HCl + HOCl – Brinn Belyea Aug 18 '14 at 3:47
• Not sure if it will form bleach or not but Chlorine itself can be used as a bleach. See this. – ashu Aug 18 '14 at 3:48

Passing chlorine gas through water yields a solution of $\ce{Cl2}$, hydrochloric acid ($\ce{HCl}$) and hypochlorous acid ($\ce{HOCl}$). The latter two are formed by reaction of chlorine with water under disproportionation.

$$\ce{Cl2 + H2O \rightleftharpoons HCl + HOCl}$$

Bleaches are chemicals which remove color by oxidation of dyes. $\ce{Cl2}$ and $\ce{HOCl}$ themselves are already strong oxidizers, but adding alkali metal hydroxides to an aqueous chlorine solution increases the solubility of $\ce{Cl2}$, and chlorine bleach is obtained, which contains alkali metal hypochlorite as active ingredient.

$$\ce{Cl2 + OH- \rightleftharpoons ClO- + Cl- + H2O}$$

Sodium hypochlorite is produced by this reaction and common household bleach is an aqueous 3-8 mass-% solution of the salt. The necessary chlorine gas is actually produced by electrolysis of $\ce{NaCl}$.

While gaseous $\ce{Cl2}$ itself can act as a bleaching agent by oxidation, the use of hypochlorite solutions has the benefit of avoiding handling of the poisonous gas. $\ce{H2}$ is a much better reducing agent, and therefore unlikely to be useful for bleaching.

A mixture of $\ce{H2}$ and $\ce{Cl2}$ will react to form gaseous hydrogen chloride when exposed to UV light. Hydrochloric acid is obtained when gaseous $\ce{HCl}$ is dissolved in water.

$$\ce{HCl + H2O \rightleftharpoons H3O+ + Cl-}$$