Example 1.4

Example . Gas Temperature/K K H /kbar Gas Temperature/K K H /kbar He . H . N . N . O . O . Table . : Values of Henry's Law Constant for Some Selected Gases in Water Argon . CO . Formaldehyde . × - Methane . Vinyl chloride . 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 diluted with helium ( . % helium, . % nitrogen and . % oxygen). · At high altitudes the partial pressure of oxygen is less than 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 . Effect of Temperature Solubility of gases in liquids decreases with rise in temperature. When dissolved, the gas molecules are present in liquid phase and the process of dissolution can be considered similar to condensation and heat is evolved in this process. We have learnt in the last Section that dissolution process involves dynamic equilibrium and thus must follow Le Chatelier’s Principle . As dissolution is an exothermic process, the solubility should decrease with increase of temperature. Liquid solutions are formed when solvent is a liquid. The solute can be a gas, a liquid or a solid. Solutions of gases in liquids have already been discussed in Section . . . In this Section, we shall discuss the solutions of liquids and solids in a liquid. Such solutions may contain one or more volatile components. Generally, the liquid solvent is volatile. The solute may or may not be volatile. We shall discuss the properties of only binary solutions, that is, the solutions containing two components, namely, the solutions of (i) liquids in liquids and (ii) solids in liquids. Let us consider a binary solution of two volatile liquids and denote the two components as and . When taken in a closed vessel, both the components would evaporate and eventually an equilibrium would be established between vapour phase and the liquid phase. Let the total vapour pressure at this stage be p total and p and p be the partial vapour pressures of the two components and respectively. These partial pressures are related to the mole fractions x and x of the two components and respectively. The French chemist, Francois Marte Raoult ( ) gave the quantitative relationship between them. The relationship is known as the Raoult’s law which states that for a solution of volatile liquids,