Bleaching Powder ($CaOCl_{2}$)

Chemical nature: Mixed salt of HCl and HOCl (hypochlorous acid)

• Contains both $Cl^{-}$ (from HCl) and O$Cl^{-}$/hypochlorite (from HOCl)
• Formula: $CaOCl_{2}$ or Ca(OCl)Cl

Preparation: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$ (Ca(OH)_{2} treated with $Cl_{2}$ gas at room temperature)

Bleaching mechanism: $CaOCl_2 + H_2O \rightarrow Ca(OH)_2 + Cl_2 \rightarrow HOCl \rightarrow HCl + [O]\ (nascent\ oxygen)$

The nascent oxygen [O] oxidizes colored organic compounds to colorless products.

Uses:

• Water purification and disinfection
• Bleaching cotton and linen textiles
• Disinfecting public swimming pools
• Stain removal

Important: Different from chlorine bleach (NaOCl solution). $CaOCl_{2}$ is a solid while NaOCl is a solution.

Stability issue: Bleaching powder gradually loses its active chlorine on storage (reacts with atmospheric $CO_{2}$ and moisture), so it is tested by "available chlorine" assay.