Question

1 mL of EDTA corresponds to 1.5 mg of hardness. 100 mL of water consumes the above EDTA before boiling 10 mL and 6 mL after boiling. Calculate permanent hardness per liter. *

Answer 1

Answer:

90 mg/L

Explanation:

1 ml EDTA is used for 1.5 mg hardness

water contains two types of hardness in the forms of calcium salts:

1) temporary hardness (can be removed by boiling the water)

2) permanent hardness (cannot be removed by boiling the water)

Unboiled water consumes 10 ml of EDTA which contains both hardness

      so total hardness    =    10 x 1.5 = 15 mg hardness

Boiled water consumes 6 ml of EDTA which contain only permanent hardness

      permanent hardness = 6 x 1.5 = 9 mg hardness

water volume = 100 ml = 0.1 L

           Hardness = $\frac{Solute}{Water Volume}$

           permanent hardness = $\frac{9}{0.1}$ = 90 mg/L