Question

In determination of hardness by EDTA method, 50ml of standard hard water required 30ml of EDTA solution while 50ml of sample hard water consumed 20ml of EDTA solution. After boiling 50ml of same sample required 10ml of EDTA solution. Calculate the permanent hardness.

(a) 322ppm

(b) 332ppm

(c) 664ppm

(d) 644ppm

The question was asked in final exam.

I would like to ask this question from Problems, Units and Formulae topic in chapter Water of Applied Chemistry

Answer 1

Right option is (b) 332ppm

For explanation: For 50ml of boiled water requires the 10ml of EDTA solution that is 10*(50/30) mg of CaCO3. The 1000ml of the boiled water requires the 10*(50/30)*20=322mg of CaCO3. It means permanent hardness is 322ppm.