Classification of Solutions based on Raoult’s law

Liquid Solutions are classified into two types on the basis of whether they obey the Raoult’s law or not. The classification is discussed as follows:

Ideal Solutions

Solutions which obey Raoult’s law irrespective of concentration in which the components are mixed are known as ideal solutions. There are two more properties followed by ideal solutions, i.e. there is no change in the enthaply or volume before and after mixing of solution components.

An ideal solution results from mixing of such components which have similar intermolecular and intramolecular forces of attraction. This can be understood by taking example of A and B as components of a solution. The solution would be ideal if A-A and B-B interactions are similar to those of A-B. Perfectly ideal solutions are rare.

Examples of some nearly ideal solutions include solutions of:

• Benzene and Toluene
• n-hexane and n-heptane
• bromoethane and chloroethane

Non Ideal Solutions

Solutions which don’t obey Raoult’s law for entire range of concentration are known as non-ideal solutions. These solutions show positive or negative deviation from the Raoult’s law depending upon whether the actual vapour pressure of the solution higher or lower than that determined by Raoult’s law.

These deviations occur due to intramolecular interactions of components being weaker or stronger than their intermolecular interactions. There are a variety of non-ideal solutions.

Some examples of non-ideal solutions include solutions of:

• Ethanol and Acetone
• Chloroform and Acetone
• Phenol and Aniline

Raoult’s Law in chemistry relates partial pressures of volatile liquid components to their mole fractions in a liquid solution. It states that the partial pressure of each component in the solution is directly proportional to its mole fraction. Thus, it helps us to calculate the total vapour pressure of the solution. Based on Raoult’s law, liquid solutions are classified as Ideal Solutions and Non-Ideal Solutions.

In this article, we will discuss the definition of Raoult’s law, ideal and non-ideal solutions, Raoult’s law for non-volatile solutes and some solved numerical problems based on Raoult’s law.