An ideal solution is one in which the attraction between components of the solution is the same as the interaction between the molecules of each component. Heat is neither absorbed nor evolved during the formation of ideal solution and the volume of the solution is equal to the sum of the volumes of the component liquids. The vapour pressures of ideal solutions can be calculated by averaging the properties of the liquids. The solutions in which properties of dissolved liquids are different from those of the liquids in the pure state and which are formed by evolution or absorption of heat are called non-ideal solutions. Raoult’s law states that partial pressures of component (say liquid A) in solution is proportional to the mole fraction. If all the components in solutions behave like ideal gases, then the total pressure of the solution is equal to the sum of the partial pressure of the individual components.

\[P_{Total} = \chi _AP_A^o + \chi _BP_B^o\]

where \(P_A^o\) and \(P_B^o\) are the vapour pressures of pure solvents A and B, respectively, and \(\chi _A\) and \(\chi _B\) are mole fractions of the solvents A and B in solution. The composition of vapour of an ideal solution can be determined by the partial pressures of the components.

If \(Y_A\) and \(Y_B\) are the mole fractions of the components A and B in the vapour phase, the partial

vapour pressures of A and B can be calculated using Dalton’s law of partial pressures.

\[P_A = Y_AP_{Total}\]

\[P_B = Y_BP_{Total}\]

A non-ideal solution is that solution (i) which does not obey Raoult’s law (ii) for which \(\Delta V_{mix}\) is not zero and (iii) for which \(\Delta H_{mix}\) is not zero. In non-ideal solutions, the solute–solvent interactions are weaker or stronger than the solute–solute and solvent–solvent interactions. The non-ideal solutions in which solute–solvent interactions are weaker or stronger than the solute– solute or solvent–solvent show positive deviations from Raoult’s law.

On adding acetone to methanol some of the hydrogen bonds between methanol molecules break. Hence

at specific composition, methanol–acetone mixture will form minimum boiling azeotrope and will show positive deviation from Raoult’s law

The answer is (1) at specific composition, methanol–acetone mixture will form minimum boiling azeotrope and will show positive deviation from Raoult’s law.

When methanol and acetone are mixed, some of the hydrogen bonds between the methanol molecules break. This is because the acetone molecules do not have any hydrogen bonding capabilities, so they disrupt the hydrogen bonds between the methanol molecules.

As a result of the broken hydrogen bonds, the vapor pressure of the solution increases. This is because the methanol molecules are now more loosely held together and are more likely to escape from the solution.

The solution will also form a minimum boiling azeotrope. This is because the methanol and acetone molecules will interact with each other more strongly than they will interact with themselves. This makes it more difficult for the molecules to escape from the solution, which raises the boiling point of the solution.

The positive deviation from Raoult's law occurs because the vapor pressure of the solution is higher than the vapor pressure predicted by Raoult's law. This is because the broken hydrogen bonds make it easier for the methanol molecules to escape from the solution.