Raoults Law

Hint: In negative deviation, the intermolecular forces in the solution are stronger.
For an ideal solution, the expected vapor pressure is calculated as a weighted average of the vapor pressures of the pure components , based on their mole fractions. Given the formula we compute:

However, the observed vapor pressure is 70 torr, which is lower than the expected 73 torr. This indicates a negative deviation from Raoult's Law, suggesting that the intermolecular attractions between the components in the solution are stronger than those in the pure components, causing a reduction in the vapor pressure.

Solution: The solution exhibits a negative deviation from Raoult's Law, as the observed vapor pressure ( 70 torr) is less than the calculated ideal vapor pressure ( 73 torr), determined using the mole fractions ( and ) and the vapor pressures of the pure components ( 63 torr and 78 torr). This deviation indicates stronger intermolecular interactions in the mixture compared to the pure components.