30g.......100%
x g........30%(impuritati)
x=9g
30-9=21g(piatra vanata fara impuritati)
M(H2O)=18 g/moli
M(CuSO4)=160 g/mol
M(CuSO4 x 5H2O) = 250 g/mol
250g......1 mol
21 g.......x moli
x=21/250
x=0.084 moli
Masa solutiei contine -291+30=321 g
1 mol CuSO4 x 5H2O.........90 g H2O
0.084 moli CUSO4 x H2O .......... x g H2O
x=7.56 g H2O
21g-7.56=13.44 g
321 g......100%
13.44....x
x=4,18%