puritatea=masa pura/masa impura*100 => m pur=puritatea*m impur/100=60*400/100=240g CaCO3
MCaCO3=ACa+AC+3AO=40+12+3*16=100g/mol
n=m/M=240/100=2,4 moli CaCO3
CaCO3 + 2HCl -> CaCl2 + CO2 + H2O
1 mol CaCO3.....................1 mol H2O
2,4 moli CaCO3.................x moli H2O
x=1*2,4/1 =