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How much bleaching powder (having 20% available chlorine) is needed to disinfect 10,000 litres of water whose chlorine demand is 1.0 mg/l? It should  be ensured that, after about 1 hour contact time, 0.2 mg/l chlorine is available.

How much bleaching powder (having 20% available chlorine) is needed to disinfect 10,000 litres of water whose chlorine demand is 1.0 mg/l? It should  be ensured that, after about 1 hour contact time, 0.2 mg/l chlorine is available. Correct Answer 68 g

Concept:

Chlorine is used as a disinfectant in water to carry out the disinfection process in water.

Some residual chlorine is left in the water to keep the water safe from future recontamination.

So Chlorine demand = Applied chlorine-Residual chlorine

The notation “bleaching powder (having x% available chlorine)” means 100kg of bleaching powder contains x kg of chlorine.

Calculation:

Given data,

Amount of water = 10,000 litres

Chlorine demand = 1.0 mg/l

Residual Chlorine = 0.2 mg/l

Applied chlorine = Chlorine demand + Residual Chlorine = 1 + 0.2 = 1.2 mg/l

For 10,000 litres of water Applied chlorine = 1.2 × 10000 = 12000 mg = 12 gm

20 gm chlorine is available in 100 gm of bleaching powder.

12 gm chlorine is available in (100/20) × 12 = 60 gm of bleaching powder

So 60 gm of bleaching powder is required.

Note: Since no answer is matching. We can take nearest as correct answer i.e. 68 gm

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