Storage Conditions and Decomposition Reactions Ranked

Optimal Storage Conditions

Bleaching powder is an unstable compound that loses its chlorine content (its strength) over time. To maximize its shelf life, it must be stored correctly:

• Cool and Dry: Store in a cool, dry place. Heat and moisture rapidly accelerate its decomposition.
• Airtight, Non-Metallic Container: It must be kept in an airtight container to protect it from moisture and carbon dioxide in the air. The container must be non-metallic (e.g., plastic or glass with a plastic-lined lid) because it corrodes metals.
• Darkness: The container should be opaque (not see-through) and stored away from direct sunlight, as UV light breaks it down.
• Isolation: Store it separately from acids, organic materials (like wood, paper, cloth), and flammable substances.

Decomposition Reactions (Ranked by Commonality/Severity)

Bleaching powder decomposes in several ways. Here they are, ranked from the most common/significant causes of strength loss during storage:

1. Decomposition by Sunlight (Photodecomposition):

   This is a very rapid decomposition. UV light from the sun provides the energy to break down the calcium hypochlorite, releasing oxygen and destroying its bleaching properties. This is why it must be stored in the dark. 
   2CaOCl₂(s) + Sunlight → 2CaCl₂(s) + O₂(g)

2. Decomposition by Moisture and CO₂ (from Air):

   This is the most common reason for spoilage in poorly sealed containers. It absorbs carbon dioxide (CO₂) from the air, which neutralizes the compound, and moisture (H₂O) causes it to release its chlorine slowly. This is why bleaching powder always has a faint smell of chlorine. 
   2CaOCl₂(s) + CO₂(g) → CaCO₃(s) + CaCl₂(s) + Cl₂O(g)

3. Decomposition by Heat (Thermal Decomposition):

   When stored in a hot place, bleaching powder will auto-decompose, releasing oxygen and chlorine, and losing its strength. This is why a "cool place" is essential.

4. Decomposition by Acids (Acute Hazard):

   This is not a storage issue but an immediate, dangerous decomposition reaction. If it comes into contact with any acid, it instantly releases all its chlorine as toxic chlorine gas. 
   CaOCl₂(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + Cl₂(g)