Question

the percentage of phosphorus in the double superphosphate

Answer 1

Ca(H₂PO₄)₂ - double superphosphate

1) Firstly need to know the molar mass
Mr(Ca(H₂PO₄)₂) = 40 + 2·(2+31+64) = 40 + 2·97 = 234 g/mol
2) Find the mass fraction by the formula
ω(R) = $\frac{Ar(R)}{Mr(RX)} * 100$, where R - element and RX - substance
ω(P) = $\frac{2*31}{234} * 100$ = 25,5 %