puritatea = m pur / m impur *100 => m pur = puritatea * m impur/100 = 50*20/100=10 g CaCO3
MCaCO3 = ACa+AC+3AO=40+12+3*16=100g/mol
a) CaCO3 = CaO + CO2
100g CaCO3..................1 mol CaO
10g CaCO3...................0,1 moli CaO
b) 100g CaCO3.......................22,4L CO2
10g CaCO3...............................x=2,24L CO2