Bleaching Powder: Uses, Strength and Safe Handling

Bleaching powder is a chlorine-releasing powder made by passing chlorine gas over slaked lime. Its active part is calcium hypochlorite, which is why it's also called chlorinated lime or chloride of lime. In water it gives off chlorine, and that chlorine does the bleaching and stain removal.

• Active compound: calcium hypochlorite, Ca(OCl)2
• CAS number: 7778-54-3 (calcium hypochlorite)
• Molar mass: about 143 g/mol for Ca(OCl)2
• Appearance: white to slightly yellowish powder with a sharp chlorine smell
• Behaviour: slowly loses strength in moist air and reacts quickly with acids, releasing chlorine gas

Household bleaching powder is weaker than the high-strength calcium hypochlorite granules used by large pool and water plants. The strength is given as available chlorine, so check the figure on the pack.

Azlok sells a Multipurpose Bleaching Powder in a 200 g pack. It's a general-purpose technical grade for cleaning, bleaching and utility work. It is not a laboratory reagent and not meant for food or medical use.

A 200 g pack is enough for several cleaning sessions. See today's price per kg to compare against bigger quantities.

• Household cleaning: removing stains and smells from toilets, bathroom floors, drains and outdoor areas.
• Bleaching: whitening cotton and linen, and in the textile and paper industries for bleaching pulp and fabric.
• Water treatment: chlorinating overhead tanks, wells and swimming pools, as done by municipal and health departments.
• Drains and garbage areas: sprinkled around drains, garbage points and wet areas to control smell, especially in the monsoon.
• Chemistry: as an oxidising agent in some reactions and in school demonstrations of chlorine release.

Making a cleaning solution: use a plastic bucket and cold water. Add the powder to the water, never water onto a heap of powder. Stir well, let the lime settle for 10 to 15 minutes, and use the clear liquid on top. The chalky sediment can leave white marks on floors.

Working out strength: grams of powder per litre = (chlorine % you want ÷ available chlorine % on the pack) × 1000. With a 30% powder, a 0.5% chlorine solution needs roughly 16 to 17 g per litre.

• Leave it on toilets or tiles for about 10 minutes, then scrub and rinse with plenty of water.
• For white cotton, use a weak, well-diluted solution, rinse thoroughly and never use it on silk, wool, nylon or coloured clothes.
• For tanks, wells and pools, follow the dose given by your local health department or pool supplier, then test chlorine with a kit before use.

Make a fresh solution each day. It loses strength within hours.

• Wear rubber gloves and keep the powder off your eyes and skin. Work with doors and windows open.
• Never mix with acids, toilet cleaners containing acid, vinegar or ammonia-based cleaners. These release toxic chlorine or chloramine gas.
• Keep it away from kerosene, oil, paint, sawdust and other organic material. It is an oxidiser and can start a fire with them.
• Store in a tightly closed plastic container in a cool, dry, shaded place. Damp and heat make it lose strength and give off fumes.
• Don't store it in metal tins. It corrodes iron.
• Keep away from children and pets. If swallowed, don't make the person vomit and see a doctor.
• Small leftover solution can go down the drain with lots of water. Don't pour it into the same drain as an acid cleaner.

For home use, buy small. Bleaching powder starts losing chlorine once the pack is opened, so a 200 g pack used within a month or two beats a big bag that sits damp in a corner. Close it tightly after every use.

Housing societies, schools, hotels and contractors who treat tanks or large areas regularly can buy more, but only if they have dry, ventilated storage. For 25 kg or more, use our bulk inquiry form and ask for the available chlorine figure on the batch.