chemistry wiz?

Question

A 20 gram sample contains a mix of Calcium Chloride and Calcium Carbonate reacted with 100 ml of 2.5M HCL, The excess HCL was then titrated with KOH. If it took 55 ml of a 2M KOH to neutralize the excess acid, what % by weight of the sample was Calcium Chloride?

Answer 1

Millimol of HCl initially = 100*2.5 = 250

Millimol of HCl left = 55*2 = 110

consumed = 140

CaCO3 + 2HCl = CaCl2 + H2O + CO2

So, millimol of CaCO3 = 140/2 = 70

Thus mass of CaCO3 = 70*100*10^-3 = 7 g

Thus % age of CaCO3 = 7*100/20 = 35 %