Percentage Composition

Example 6.7.1:

Calculate the percentage by mass of Nitrogen in trioxonitrate (V) acid. (H = 1, N = 14, O = 16)

Solution:

HNO₃

 1 + 14 + 16 × 3.

Relative Molecular Mass = 63

N = 14

% by mass of Nitrogen = \( \frac{14}{63} \: \times \: \frac{100}{1} \\ = \scriptsize 22.2 \% \)

Example 6.7.2:

Calculate the percentage composition of all the components elements in calcium trioxocarbonate (IV) (CaCO₃)
(Ca = 40, C = 12, O = 16)

Solution:

Relative molecular mass = 40 + 12 + (16 x 3)  =  100

% by mass of calcium = \( \frac{40}{100} \: \times \: \frac{100}{1} \\ = \scriptsize 40 \% \)

% by mass of carbon = \( \frac{12}{100} \: \times \: \frac{100}{1} \\ = \scriptsize 12 \% \)

% by mass of oxygen = \( \frac{48}{100} \: \times \; \frac{100}{1} \\ = \scriptsize 48 \% \)

Note:  The results above can be interpreted as follows: 100 g of calcium trioxocarbonate (IV) contains 40 g of calcium, 12 g of carbon, and 48 g of oxygen. The percentage by mass of any element also represents its reacting mass in forming that compound.