1 L of pond water contains 20 mg ofCa2+ and 12mg of Mg2+ ions. What is the volume of a 2N Na2CO3 solution required to soften 5000 L of pond water?

Milli- equivalents of Ca2++ milli-equivalents of Mg2+= milli-equivalents of Na2CO3:2040+1224=V×2 ∵milli equivalents=Wt.E∴V = 12=0.5 ml /litFor 5000 L of pond waterV=5000×0.5 =2500 ml                      =2.5 lit