Question

A hydrated calcium phosphate contains 7.14 % water of crystallization the molecular mass of phosphate is 252. The percentage composition is 15.18 % Ca, 24.6% P, 4% H and 57.11 % Oxygen what is the molecular formula of the compound?

Answer 1

Answer:

Explanation:

Calculating the percentage composition of the given numbers -

          Number of moles          Simplest ratio            Whole number  

Ca   =  15.18 / 40 = 0.38           0.38 / 0.38 = 1                   1

P          24.6 / 31 = 0.79            0.79 / 0.38 = 2.07             2

H         4 / 1       =   4                  4 / 0.38 = 2.63                  3

O         57.11 / 16 = 3.57           3.57 / 0.38 = 9.39              9

H2O    7.14 / 18  = 0.397         0.397 / 0.38 = 1.04             1

Hence, the simple ratio of percentage to mass ratio,  

Ca : P : H : O = 0.4 : 0.8 : 4 : 3.6 = 1 : 2 : 10 : 9 ( Taking upto one decimal point)

Thus,  the empirical formula formed will be  =  Ca P2H3O9. H2O

Mass of empirical formula =  171

Molecular formula  =  empirical formula/ n

=  252 / 171 = 1.47 or 2

Thus, the molecular formula = Ca2P4H6O18 . 2H2O