A city supplies of 15,000 m³ of water per day treated with chlorine with dosage of 0.5 ppm. For this purpose, the requirement of 25% bleaching powder per day would be
- A30 kgCorrect
- B75 kg
- C300 kg
- D20 kg
Solution
Concept
Quantity of bleaching powder for chlorination
Formula
Chlorine = dose (g/m³) × volume (m³); Bleaching powder = chlorine / (% available chlorine)
Step-by-step solution
1. Dose 0.5 ppm = 0.5 g/m³. 2. Chlorine needed per day = 0.5 × 15,000 = 7,500 g = 7.5 kg. 3. Bleaching powder with 25% available chlorine = 7.5 / 0.25 = 30 kg.
Explanation
1 ppm in water is 1 g/m³. The mass of chlorine needed is the dose times the volume, and the bleaching powder required is more because it contains only 25% available chlorine.
Shortcut
kg of bleaching powder = (dose in mg/L × flow in m³) / (1000 × fraction of chlorine).
Common mistake
Forgetting to divide by 0.25.
Correct answer: A) 30 kg