Q114 / 200 · MHT CET - Medical 2026 (22 April Shift 2) · Chemistry
Which of the following statements is NOT true about the ideal solution?
- AIt obeys Raoult's law over the entire range of concentration.
- BThere is no heat evolved or absorbed when two components forming an ideal solution are mixed.
- CThere is no volume change when two components forming an ideal solution are mixed.
- Correct answerDThe vapor pressure of the ideal solution can be higher or lower than those of pure components
Solution
For an ideal solution, the following conditions hold true:
1. It obeys Raoult's law over the entire range of concentration.
2. The enthalpy of mixing is zero, i.e., $\Delta H_{mix} = 0$. No heat is evolved or absorbed.
3. The volume of mixing is zero, i.e., $\Delta V_{mix} = 0$.
4. The total vapor pressure of the solution is given by $P_{total} = P_{A}^{0} x_{A} + P_{B}^{0} x_{B}$. Since $x_{A} + x_{B} = 1$, the total vapor pressure is a weighted average of the vapor pressures of the pure components. Therefore, the vapor pressure of an ideal solution always lies between the vapor pressures of the pure components. It cannot be higher or lower than both.
Thus, the statement that the vapor pressure of the ideal solution can be higher or lower than those of pure components is incorrect.
Answer: The vapor pressure of the ideal solution can be higher or lower than those of pure components
1. It obeys Raoult's law over the entire range of concentration.
2. The enthalpy of mixing is zero, i.e., $\Delta H_{mix} = 0$. No heat is evolved or absorbed.
3. The volume of mixing is zero, i.e., $\Delta V_{mix} = 0$.
4. The total vapor pressure of the solution is given by $P_{total} = P_{A}^{0} x_{A} + P_{B}^{0} x_{B}$. Since $x_{A} + x_{B} = 1$, the total vapor pressure is a weighted average of the vapor pressures of the pure components. Therefore, the vapor pressure of an ideal solution always lies between the vapor pressures of the pure components. It cannot be higher or lower than both.
Thus, the statement that the vapor pressure of the ideal solution can be higher or lower than those of pure components is incorrect.
Answer: The vapor pressure of the ideal solution can be higher or lower than those of pure components
Hence, the correct answer is option: 'D'.