CBSE Class 12 · 2001 · All India Compartment · SolutionsShort Answer

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For determining molar masses of macromolecular substances in solution, the osmotic pressure measurement method is preferred over measurement of any other colligative property. Give two reasons for it.

Solution

(i) Macromolecules give solutions of very low molality, for which

Δ T_{b}

and

Δ T_{f}

are too small to be measured; the osmotic pressure of even such dilute solutions is appreciable and measurable.
(ii) Osmotic pressure is measured at room temperature, so polymers and proteins that are unstable on heating are not decomposed. (Molarity, used in

π = C R T

, is also directly obtained at that temperature.)

CBSE Class 12 Board · 2001 · All India Compartment · Subjective

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