Which compounds contain more phosphorus, Ca3 (PO4) 2 or CaHPO4 in mass percent?

1. Find the proportion of phosphorus in calcium phosphate:

w (P) = 2 * Ar (P): M (Ca3 (PO4) 2;

M Ca3 (PO4) 2) = 40 * 3 + 31 * 2 + 16 * 4 * 2 = 310 g / mol;

w1 (P) = 2 * 31: 310 = 0.2 or 20%;

2. find the proportion of phosphorus in calcium hydrogen phosphate:

w (P) = Ar (P): M (CaHPO4);

M (CaHPO4) = 40 + 1 + 31 + 16 * 4 = 136 g / mol;

w2 (P) = 31: 136 = 0.2279 or 22.79%;

3.determine in which case the mass fraction of phosphorus is greater:

w2 (P) – w1 (P) = 22.79% – 20% = 2.79%.

Answer: phosphorus is 2.79% more in calcium hydrogen phosphate.