Question

Which of the following does not belong to an ideal solution?

• A. \( \Delta H_{\text{mix}} = 0 \)
• B. \( \Delta V_{\text{mix}} = 0 \)
• C. Obeys Raoult's law over the entire range of concentration
• D. Does not obey Raoult's law

Hint:

For an ideal solution, both the enthalpy and volume of mixing are zero, and Raoult's law is followed across all concentrations. Non-ideal solutions show deviations from this behavior.

Answer 1

The Correct Option is D

An ideal solution is one in which the enthalpy of mixing \( \Delta H_{\text{mix}} = 0 \), and the volume of mixing \( \Delta V_{\text{mix}} = 0 \), meaning there is no heat or volume change upon mixing the components. Furthermore, an ideal solution obeys Raoult's law throughout the entire concentration range, which means the vapor pressure of the solution is directly proportional to the mole fraction of the solvent. However, a solution that does not obey Raoult's law is not considered ideal. Deviations from Raoult's law can occur due to interactions between different components in non-ideal solutions, causing either positive or negative deviations from the expected behavior. Thus, the correct option is (4), which states that such a solution does not obey Raoult's law.

Answer 2

Step 1: Understand the concept of an ideal solution
An ideal solution is one in which the intermolecular forces between unlike molecules are similar to those between like molecules.
In such solutions, the components mix without any change in enthalpy or volume.

Step 2: Raoult's law in ideal solutions
Ideal solutions obey Raoult's law, which states that the partial vapor pressure of each component is proportional to its mole fraction in the solution.
Mathematically, \( P_i = X_i P_i^0 \), where \( P_i \) is the partial pressure and \( X_i \) is the mole fraction.

Step 3: Non-ideal solution characteristics
Solutions that do not obey Raoult's law exhibit deviations, either positive or negative, due to differences in intermolecular forces.
These are called non-ideal solutions.

Step 4: Conclusion
Therefore, a solution that does not obey Raoult's law does not belong to an ideal solution.