Bleaching powder, also known as chloride of lime, is a compound with the chemical formula Ca(OCl)2. It has traditionally been used as a bleaching agent in the paper and textile industries as well as for domestic sanitation and disinfection purposes.
Composition and Properties
Bleaching powder is composed of calcium hypochlorite and calcium chloride. When produced, a mixture of slaked lime (calcium hydroxide) and chlorine gas reacts to form bleaching powder.
Ca(OH)2 + Cl2 → Ca(OCl)2 + CaCl2
The active ingredient is calcium hypochlorite (Ca(OCl)2), which makes up around 35% of bleaching powder by mass. The remaining 65% is calcium chloride (CaCl2), which acts as a stabilizer and prevents the hypochlorite from decomposing too quickly.
Bleaching powder is a white or off-white crystalline solid. It has a characteristic chlorine-like odor. When exposed to air and moisture, it decomposes slowly and releases chlorine gas. This property makes it useful as a disinfectant. Bleaching powder is only sparingly soluble in water but the hypochlorite ion (OCl-) it releases acts as a strong oxidizing agent in solution.
Uses of Bleaching Powder
The main uses of bleaching powder take advantage of its ability to release hypochlorite ions in solution:
- Bleaching of textiles and paper: Hypochlorite bleaches cellulose fibers by breaking carbon-carbon double bonds in colored compounds like dyes and lignin. This decolorizes the material.
- Water treatment: As a disinfectant, bleaching powder is used to purify municipal water supplies by killing bacteria and other microbes. The released chlorine acts as a potent germicide.
- Swimming pool sanitization: Calcium hypochlorite from bleaching powder is a common ingredient in pool chlorination tablets and granules used to keep pools clean and safe.
- Household cleaning: Bleaching powder solution is effective at bleaching and disinfecting surfaces. It helps remove stains and kill household germs.
- Agriculture: Used as a soil disinfectant and to control plant diseases in orchards and fields by inhibiting microbial growth in soil.
Safety and Environmental Issues
While an effective disinfectant and bleaching agent, bleaching powder also poses certain risks that require safety precautions:
- Chlorine gas: Prolonged exposure to chlorine gas released during decomposition can damage lungs and eyes. Proper ventilation is important when handling bleaching powder.
- Skin and eye irritation: Direct contact with skin can cause irritation, burns or bleaching of skin. Gloves and eye protection should be worn.
- Water pollution: Large amounts of bleaching powder residues released into water bodies can harm aquatic life by increasing chlorine levels.
- Alternatives: Other chlorine-based disinfectants are increasingly favored over bleaching powder due to environmental concerns. Sodium hypochlorite is a common replacement.
In conclusion, bleaching powder has historically served many useful applications but safer alternatives are now preferred due to its chlorine content and potential risks if not handled and disposed of properly. With care and precautions, it remains a viable disinfecting and bleaching agent even today.