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Chemistry: Solutions: Types of Solutions and Conditions for Validity of Henry՚s Law

Types of Solutions

  • Solutions can be solid, liquid or gaseous.
  • Depending upon the physical state of the solute and the solvent, there are nine possible types of solutions.
  • The different types of solutions are given in the table below:
Illustration: Types of Solutions

Liquid in Liquid

In the solution of liquids in liquids such as alcohol in water, the constituent present in smaller amounts is solute and the constituent present in larger amounts is called as solvent.

When two liquids are mixed, three different situations arise:

  • Both the liquids are completely miscible (dissolve in each other in all proportions) e. g. , alcohol and water, benzene and toluene.
  • The liquids are partially miscible (dissolve in each other only to a certain extent) e. g. , water and phenol.
  • The liquids are immiscible (do not dissolve in each other) e. g. water and benzene, water and toluene.

The solubility of liquids in liquids generally increases with rise in temperature.

Gases in Liquid

  • The gases are generally soluble in liquids.
  • Oxygen is sufficiently soluble in water, which allows the survival of aquatic life in ponds, rivers and oceans.
  • Gases like CO2 and NH3 are highly soluble in water.
  • The solubility of a gas in a liquid depends on the pressure, temperature and the nature of the gas and the solvent.

Effects of Pressure

  • The variation of solubility of a gas in a liquid with pressure is governed by Henry՚s law.
  • Henry՚s law states that “The mass or mole fraction, of a gas dissolved in a solvent is directly proportional to the partial pressure of the gas” Henry՚s law is represented by

where K = constant

p = partial pressure of the gas

x = the mole fraction of the gas in the solution.

Conditions for Validity of Henry՚s Law

It is found that gases obey Henry՚s law under the following conditions:

  • The pressure is not too high.
  • The temperature is not too low.
  • The gas does not dissociate, associate or enter into any chemical reaction with the solvent.

Effect of Temperature

  • The solubility of a gas in a liquid at constant pressure decreases with rise in temperature.
  • The solubility of CO2 in water at 20°C is 0.88 cm3 per cm3 of water.
  • When a solution containing gas is heated some gas is usually expelled from the solution.

Effect of the Nature of the Gas and the Solvent

Gases like CO2, HCl and NH3 are highly soluble in water where as H2, O2 and N2 are less soluble.

Solids in Liquids

  • When a solid is dissolved in a liquid, the solid is referred as the solute and the liquid as the solvent.
  • Different substances dissolve to different extent in the same solvent.

Vapour Pressure

The pressure exerted by the vapour of the liquid in such a case is called the vapour pressure of the liquid.