-calculez masa de Ca pur
p= m,px100/m,i....................p=puritatea
80/100= mp/40----> m,p= 32g Ca pur
-din ecuatia reactiei calculez masa de acid,cu masa molara 36,5g/mol
1mol....2mol
Ca + 2HCl--------> CaCl2 + H2
40g.....2x36,5g
32g...........x..........................................calculeaza x=m,HCl