Vapour Pressure of Solutions of Solids in Liquids — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Vapour Pressure of Solutions of Solids in Liquids.

Combined Colligative Property Problems

high

NEET often tests the interconnectedness of colligative properties. A question might provide vapour pressure lowering data and then ask for the boiling point elevation or freezing point depression of the same solution, or vice-versa. This requires students to first calculate the mole fraction of the solute from vapour pressure data and then use that mole fraction (or molality derived from it) in the formulas for other colligative properties. This tests a deeper understanding and ability to link concepts.

Graphical Representation and Interpretation

medium

While less common, questions could involve interpreting graphs of vapour pressure versus mole fraction. For an ideal solution with a non-volatile solute, the graph of $P_A$ vs $x_A$ is a straight line passing through the origin and $P_A^0$ at $x_A=1$. Students might be asked to identify such a graph, or interpret deviations from linearity for non-ideal solutions (though detailed non-ideal behavior is less emphasized for NEET). This tests visual and analytical skills beyond direct formula application.

Impact of Electrolytes (van't Hoff factor)

medium

Although the core topic is 'solids in liquids' which often implies non-electrolytes, NEET frequently includes questions involving electrolytes where the van't Hoff factor ($i$) must be considered. A question might ask about the vapour pressure lowering of a solution containing NaCl or CaCl$_2$. Students would need to account for the dissociation of these solutes, multiplying the calculated moles of solute by $i$ to get the effective number of particles. This adds a layer of complexity to the mole fraction calculation.