How many grams of phoshphorus are in a sample of Ca3(PO4)2 that contains 41.0 g of calcium? ?

Question

How many grams of phoshphorus are in a sample of Ca3(PO4)2 that contains 41.0 g of calcium? ?

Answer 1

First we calculate the Mr (molecular mass) of Ca3(PO4)2

Ca = 40.08 x 3

P = 30.97 x 2

O = 16.00 x 8

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Ca3(PO4)2 = 310.18 g/mol

so we must calculate the masses of Ca3(PO4)2 that contains 41.0 g of Ca by this :

g Ca = (3 x Ar Ca / Mr Ca3(PO4)2 ) x g Ca3(PO4)2

41.0 = (3 x 40.08/310.18) x g Ca3(PO4)2

41.0 = 0.39 x g Ca3(PO4)2

g Ca3(PO4)2 = 105.77 g

because the masses of Ca3(PO4)2 is known thus we can calculate the mass of P

g P = [ 2 x Ar P / Mr Ca3(PO4)2] x g Ca3(PO4)2

g P = ( 2 x 30.97 / 310.18) x 105.77

g P = 21.12 g