Question

How much bleaching powder is needed to chlorinate \(5000\) litres of water whose chlorine demand is \(2\) mg/l, assuming that the bleaching powder has \(25\%\) available chlorine?

• A. \(4\) g
• B. \(40\) g
• C. \(140\) g
• D. \(400\) g

Hint:

For chlorination, \[ \boxed{ \text{Bleaching Powder} = \frac{\text{Required Chlorine}} {\%\text{ Available Chlorine}/100} } \] Always convert mg to grams before calculating the final answer.

Answer 1

The Correct Option is B

Concept: The quantity of bleaching powder required depends upon the chlorine demand of water and the percentage of available chlorine in the bleaching powder. The required chlorine is calculated as \[ \boxed{ \text{Chlorine Required}= (\text{Chlorine Demand})\times(\text{Volume of Water}) } \] The quantity of bleaching powder is \[ \boxed{ \text{Bleaching Powder} = \frac{\text{Required Chlorine}} {\text{Fraction of Available Chlorine}} } \]

Step 1: Calculate the chlorine requirement. Given, \[ \text{Volume}=5000\text{ L} \] \[ \text{Chlorine Demand}=2\text{ mg/L} \] Therefore, \[ \text{Required Chlorine} = 5000\times2 = 10000\text{ mg} = 10\text{ g} \]

Step 2: Calculate the bleaching powder required. Available chlorine \[ =25\%=0.25 \] Hence, \[ \text{Bleaching Powder} = \frac{10}{0.25} = 40\text{ g} \] Thus, \[ \boxed{40\text{ g}} \] Therefore, the correct option is \[ \boxed{(B)\;40\text{ g}.} \]