Question

We know that lime required for softening of water is x{temp Ca hardness + 2.Mg hardness + perm(Mg+Fe+3Al)hardness + 1/2 HCL + H2SO4 – NaAlO2 – CO2}-all are in terms of mg of CaCO3. Here x=?

(a) 7.4

(b) 0.74

(c) 74

(d) 740

I had been asked this question in an online interview.

I need to ask this question from Problems, Units and Formulae in portion Water of Applied Chemistry

Answer 1

Right choice is (b) 0.74

To elaborate: Lime also reacts with bicarbonates of Na and K to form carbonate. Since 100 parts of CaCO3 is equivalent to the 74 parts of Ca(OH)2. so, x=74/100=0.74.