Question

Irrespective of the source, a pure sample of water always yields $88.89\%$ oxygen by mass and $11.11\%$ hydrogen by mass. This is explained by the law of:

• A. conservation of mass
• B. constant proportion
• C. multiple proportion
• D. none of these

Answer 1

Answer: (B)

constant proportion

The molecular mass of water is 18 amu.

Molecular mass of oxygen is 16 amu. So, % of oxygen in $H_{2}O$ is $\frac{16}{18}\times 100=88.89\%.$.

Molecular mass of hydrogen is 2 amu. So, % of hydrogen in $H_{2}O$ is$\frac{2}{18}\times 100=11.11\%.$.

According to the law of constant proportions, a chemical compound always contains the same elements combined in the same proportion by mass. For example, pure water obtained from different sources such as rivers, wells, springs, seas, etc., always contains hydrogen and oxygen together in the ratio of 1:8 by mass.