Percent Composition — lesson. Science State Board, Class 10.

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We have learnt the number of entities present in a given substance so far. However, the percentage of a specific element present in a compound is frequently required.

The percentage composition of a compound represents the mass of each element present in

$100$

$g$ of the compound.

The formula for calculating the mass percent of an element is given below:

$Mass percent of an element = \frac{Mass of the element in the compound}{Molecular mass of the compound} \times 100$

Let us look at few examples for calculating percentage composition.

Example:

$1$

Calculate the mass percent of water (

$H_2O$ ).

Solution:

$Molecular mass of H_{2} O = 2 (1) + 16 = 18 g$

$\begin{array}{l} Mass percent of hydrogen = \frac{2}{18} \times 100 = 11.11 % \\ Mass percent of oxygen = \frac{16}{18} \times 100 = 88.89 % \end{array}$

Example: $2$

Calculate the mass percent of methane (

$CH_4$ ).

Solution:

$Molecular mass of {CH}_{4} = 12 + 4 = 16 g$

$\begin{array}{l} Mass percent of carbon = \frac{12}{16} \times 100 = 75 % \\ Mass percent of hydrogen = \frac{4}{16} \times 100 = 25 % \end{array}$

This percentage composition is used for determining the empirical formula and molecular formula.

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11. Percent Composition

Theory: