Write and explain Henry's law. Also write its application.

Explanation

Henry was the first to give a quantitative relation between pressure and solubility of a gas in a solvent which is known as Henry.s law. The law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas.
Dalton, a contemporary of Henry, also concluded independently that the solubility of a gas in a liquid solution is a function of partial pressure of the gas.
If we use the mole fraction of a gas in the solution as a measure of its solubility, then it can be said that the mole fraction of gas in the solution is proportional to the partial presure of the gas over the solution.
The most commonly used form of Henry.s law states that ..the partial pressure of the gas in vapour phaser (p) is proportional to the mole fraction of the gas (x) in the solution.. and is expressed as :
Here, `K_(H)` is the Henry.s law constant.
If we draw a graph between partial pressure of the gas versus mole fraction of the gas in solution, then we should get a plot of the type as shown in Fig.

Experimental results for the solubility of HCl gas in cyclohexane at 293 K. The slope of the line is the Henry.s Law constant, `K_(H)`.
Different gases have different `K_(H)` values at the same temperature. This suggests that `K_(H)` is a function of the nature of the gas.
Higher the value of `K_(H)` at a given pressure, the lower is the solubility of the gas in the liquid.

Henry.s law finds several applications in industry and explains some biological phenomena. Notable among these are :
To increase the solubility of `CO_(2)` in soft drinks and soda water, the bottle is sealed under high pressure.
Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure underwater. Increased pressure increases the solubility of atmospheric gases in blood. When the divers come towrds surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends, which are painful and dangerous to life.
To avoid bends, as well as, the toxic effects of high concentrations of nitrogen in the blood, the tanks used by scuba divers are filled with air dilluted with helium (11.7 % helium, 56.2% nitrogen and 32.1% oxygen).
At high altitudes the partial pressure of oxygen is less then that at the ground level. This leads to low concentrations of oxygen in the blood and tissues of people living at high altitudes or climbers. Low blood oxygen causes climbers to become weak and unable to think clearly, symptoms of a condition known as anoxia.