Calculate the mass fractions of elements in the compounds H3PO4, Ca (NO3) 2.

To find the mass fraction of an individual element that is part of a substance, we use the formula:

w% (element) = Mr (element): Mr (substance) * 100%.

Using this formula, we find the mass fractions of elements in the following compounds:

a) H3PO4:

w% (H) = (3 * 1): 98 * 100% = 3%;

w% (P) = 31: 98 * 100% = 31.6%,

then oxygen accounts for 100% – 31.6% – 3% = 65.4%.

b) Ca (NO3) 2:

w% (Ca) = 40: 164 * 100% = 24.4%;

w% (N) = (2 * 14): 164 * 100% = 28: 164 * 100% = 17%,

then oxygen accounts for 100% – 17% – 24.4% = 58.6%.