**Ideal solutions: ** The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions. Ideal solutions are formed by mixing the two components which are identical in molecular size, in structure and have almost identical intermolecular forces.

**Examples:**

1. Benzene and toluene

2. n – Hexane and n-Heptane

3. Chiorobenzene and bromobenzene.

**Characteristics: **

1. They must obey Raoult’s law.

2. ∆H mixing should be zero.

3. ∆W mixing should be zero, i.e. volume change on mixing is zero.

**Non – ideal solutions: ** The solutions which do not obey Raoult’s law are called non-ideal solutions. In case of non – ideal solutions there is a change in volume and heat energy when the two components are mixed.

**Characteristics:**

1. They does not obey Raoult’s law.

2. ∆V_{mix} ≠ 0

3. ∆H_{mix} ≠ 0

**Behaviour of Ideal Solutions: **A plot of P_{1} or P_{2} versus the mole fraction x_{1} and x_{2} for an ideal solution gives a linear plot. These Lines (I and II)pass through the points and respectively when x_{1} and x_{2} is equal to unity.

Similarly the plot (Line III) of P_{toal} versus x_{2} is also linear. The minimum value of is P_{1}° and the maximum value is P_{2}° , assuming that component 1 is less volatile than component 2, i.e. P_{1}° < P_{20}.