Question

H3PO4, Phosphoric acid, is used in detergents, fertilizers, toothpastes and flavoring in carbonated beverages. Calculate the percent composition by mass to two decimal places of H, P and O in this compound.

Answer 1

Hydrogen atomic mass : 1 amu
Oxygen atomic mass:  16 amu
Phosphorus atomic mass : 31  amu   (30.97+)

compound: H3 PO4:  Total = 3 * 1+ 31 + 16 * 4 = 98 amu

% by mass of Hydrogen: 100*1/98 = 1.02 %
                    of Oxygen:   100* 64 /98 = 65.31 %  rounded number
                    of Phosphorous: 100* 31 / 98 = 31.63%

Answer 2

Answer:

Hydrogen atomic mass : 1 amu

Oxygen atomic mass:  16 amu

Phosphorus atomic mass : 31  amu   (30.97+)

compound: H3 PO4:  Total = 3 * 1+ 31 + 16 * 4 = 98 amu

% by mass of Hydrogen: 100*1/98 = 1.02 %

                   of Oxygen:   100* 64 /98 = 65.31 %  rounded number

                   of Phosphorous: 100* 31 / 98 = 31.63%