Crystallisation, Distillation, Chromatography — Predicted 2026
AI-Predicted Question Angles for UPSC 2026
Application of specific distillation types
highNEET frequently tests the ability to choose the correct distillation method based on the properties of the liquid mixture. Questions will likely involve scenarios like separating liquids with close boiling points (fractional), heat-sensitive compounds (vacuum), or water-immiscible volatile compounds (steam). Students need to differentiate between these applications clearly, understanding the underlying principles that make each method suitable for its specific purpose. This requires more than just memorization; it demands a conceptual grasp of how each technique works.
Chromatography principles and $R_f$ value calculation
mediumChromatography, especially TLC, is a versatile technique. Questions are highly probable on the roles of stationary and mobile phases, the concept of differential adsorption/partition, and the calculation of the $R_f$ value. A common question type involves providing distances traveled by the spot and solvent front and asking for the $R_f$ value, or vice-versa. Understanding how $R_f$ values relate to compound identification and purity assessment is also a key area. Conceptual questions on factors affecting $R_f$ (e.g., solvent polarity) could also appear.
Ideal solvent characteristics and process steps in crystallisation
mediumCrystallisation is a fundamental purification method for solids. Questions often focus on the characteristics of an ideal solvent (differential solubility, non-reactivity) and the importance of specific steps in the process, such as slow cooling for crystal purity and size, or hot filtration to remove insoluble impurities. Misconceptions related to these steps (e.g., effect of rapid cooling) are common traps. A question might ask to identify the correct sequence of steps or the purpose of a particular step in crystallisation.