Question

What is an ideal solution? Mention the characteristics of an ideal solution.

Hint:

An ideal solution obeys Raoult's law at all concentrations with zero enthalpy and zero volume change of mixing.

Answer 1

Step 1: Definition. An ideal solution is a solution that obeys Raoult's law over the entire range of concentration, at all temperatures. That is, the partial vapour pressure of each component equals its mole fraction times the vapour pressure of the pure component: \( p_A = x_A p_A^{\circ} \) and \( p_B = x_B p_B^{\circ} \).
Step 2: Molecular reason. In an ideal solution the intermolecular forces between the two different molecules A–B are nearly the same as the forces A–A and B–B in the pure liquids. Example: benzene and toluene, or n-hexane and n-heptane.
Step 3: Characteristics.
(i) It obeys Raoult's law at every concentration.
(ii) Enthalpy of mixing is zero: \( \Delta H_{mix} = 0 \) (no heat absorbed or released on mixing).
(iii) Volume change on mixing is zero: \( \Delta V_{mix} = 0 \) (total volume equals the sum of the volumes of the components).
Step 4: Conclusion. Hence an ideal solution shows no deviation from Raoult's law, with \( \Delta H_{mix} = 0 \) and \( \Delta V_{mix} = 0 \) because A–B interactions equal A–A and B–B interactions. \[ \boxed{\Delta H_{mix} = 0,\ \Delta V_{mix} = 0} \]