CaSO4的质量为1.361g,结晶水的质量==1.721-1.361==0.36g,
n(CaSO4)=1.361/136=0.01 mol;n(H2O)=0.36/18=0.02 mol,
CaSO4.xH2O==CaSO4 + x H2O
1 x
0.01 0.02
所以x=2 mol