Дано
m(Ca3PO4)2)=15.5 g
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m(P)-?
4P+5O2-->2P2O5
P2O5+3H2O-->2H3PO4
2H3PO4+3CaCL2-->Ca3(PO4)2+6HCL
M(Ca3(PO4)2)=310 g/mol
n(Ca3(PO4)2)=m/M=15.5/310=0.05 mol
4n(P)=n(Ca3(PO4)2
n(P)=4/2*0.05=0.1 mol
M(P)=31 g/mol
m(P)=n(P)*M(P)=0.1*31=3.1 g
ответ 3.1 г
4Li+O2=2Li2O
Li2O+H2O=2LiOH
2LiOH+H2SO4=Li2SO4+2H2O
Li2SO4+BaCl2=2LiCl+BaSO4
2Fe(OH)3+9NO2⇒2Fe(NO3)3+ 3NO+3H2O
Удачи!!!