Question

50 ml of standard and hard water containing 1mg of pure CaCO3 per ml consumed 10ml of EDTA solution. 50ml of given EDTA sample requires 10ml of same EDTA solution. Calculate the total hardness of water sample in ppm.

(a) 10ppm

(b) 100ppm

(c) 1000ppm

(d) 10000ppm

The question was posed to me in semester exam.

My doubt stems from Problems, Units and Formulae in chapter Water of Applied Chemistry

Answer 1

The correct option is (c) 1000ppm

The best I can explain: 50ml of standard hard water requires 10ml of EDTA solution so 1ml of standard water requires 5ml of EDTA solution. So, 50ml of water sample requires 10ml of EDTA solution. So, 50ml of water sample requires 50mg of CaCO3. So, 1000ml of water sample requires 50*(1000/50)=1000 mg of CaCO3 that is 1000ppm.