Question

What is the mass of impurity in a sample of CaCo3, if 0.040 mole of Co2 was formed when 5.0g of the sample reacted with excess dilute hcl.

Answer 1

CaCO3 + 2HCl ==> CaCl2 + H2O + CO2

0.04 moles CO2 would come from 04 x 100 = 4.0 grams CaCO3
% purity = (4.0/5.0)*100 = 80%.