Question

Write a note on the discovery of oxygen.

Answer 1

Oxygen

The second-largest component of air, oxygen is very important for the survival of human beings, plants and animals.

Discovery of oxygen

• Antoine Lavoisier, a french scientist proved that air is a mixture of gases.
• With the help of an experiment conducted in 1776, he showed that nitrogen and oxygen are the main constituents of air.
• Lavoisier heated some mercury in a retort. The end of the retort was connected to a bell jar that consisted of air. The bell jar was kept inverted over mercury contained in a trough.

Lavoisier's observation

• A red layer of mercuric oxide was formed on the hot surface of the mercury in the retort.
• The level of mercury in the bell jar rose by 1/5th of the total volume of the bell jar.

Lavoisier's conclusions

• Mercury used 1/5th portion of air in the bell jar to form the red substance called active air. This gas supported combustion better than air and was named oxygen by Lavoisier. This gas also supported life.

$$\begin{gathered} 2\mathrm{Hg}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\stackrel{\mathrm{heat}}{\to }2\mathrm{HgO}\left(\mathrm{s}\right) \\ \mathrm{Mercury}\mathrm{Oxygen}\mathrm{Mercury}\left(\mathrm{II}\right)\mathrm{oxide} \end{gathered}$$

Mercury (II) oxide was heated to obtain mercury and oxygen.

$$\begin{gathered} 2\mathrm{HgO}\left(\mathrm{s}\right)\stackrel{\mathrm{heat}}{\to }2\mathrm{Hg}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ \mathrm{Mercury}\left(\mathrm{II}\right)\mathrm{oxide}\mathrm{Mercury}\mathrm{Oxygen} \end{gathered}$$

• The remaining 4/5th portion of air in the bell jar did not support combustion and was called inactive air. This gas was named azote meaning not suitable for life. Later the gas was named nitrogen.

From the above experiment, it was clear that nitrogen and oxygen are present in the air in a ratio of 4:1 by volume. Other gases are present in very small amounts in the air.