Question

a student heated 21.5 g pure hydrated calcium sulfate ,CaSO4 x H2O .17.0 g anhydrous calcium sulfate was formed .Determine the molecular formula for this hydrated salt

Answer 1

CaSO₄•H₂O->(t) CaSO₄+H₂O

m(CaSO₄)=17g

m(CaSO₄•xH₂O)=21.5g

M(CaSO₄•xH₂O)=m(CaSO₄•xH₂O)*M(CaSO₄)/m(CaSO₄)=21.5*136/17=172g/mol

x=(M(CaSO₄•xH₂O)-M(CaSO₄))/18=(172-136)/18=2

CaSO₄•2H₂O