NCERT · Class 12 · Chemistry · SolutionsState Henry's Law and write its mathematical expression. Discuss any three important applications of Henry's Law and mention its limitations.

Statement of Henry's Law\nHenry's Law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution.

Mathematical Expression\nIf $x$ is the mole fraction of the gas in the solution and $p$ is the partial pressure of the gas over the solution, then according to Henry's law:

$$p = K_H \cdot x$$\nWhere $K_H$ is Henry's law constant. Different gases have different $K_H$ values at the same temperature, indicating that $K_H$ is a function of the nature of the gas.

Important Applications of Henry's Law

1. Production of Carbonated Beverages: To increase the solubility of $CO_2$ in soft drinks and soda water, the bottles are sealed under high pressure. When the bottle is opened, the partial pressure decreases, resulting in the effervescence of $CO_2$.
2. Scuba Diving (Deep Sea Diving): Scuba divers breathe compressed air while deep in the ocean. Under high pressure underwater, the solubility of atmospheric gases like nitrogen and oxygen in blood increases significantly. When the diver surfaces, the pressure decreases rapidly, causing dissolved nitrogen gas to form bubbles in the blood, leading to a painful and dangerous medical condition known as 'bends'. To avoid this, tanks are diluted with helium (11.6%), nitrogen (56.2%), and oxygen (32.1%).
3. At High Altitudes: At high altitudes, the partial pressure of oxygen is low compared to sea level. This leads to low concentrations of oxygen in the blood and tissues of people living there or climbers, causing a medical condition known as anoxia, where climbers become weak and unable to think clearly.

Limitations of Henry's Law\nHenry's law is valid only under certain specific conditions:

• The pressure of the gas is not too high.
• The temperature is not too low.
• The gas does not undergo any chemical association or dissociation in the solvent (e.g., ammonia or hydrogen chloride gas dissolved in water do not obey Henry's law strictly because they ionize or react).