JEE Main201910 Jan 2019Evening ShiftChemistrySolutionsActual
The elevation in boiling point for 1 molal solution of glucose is 2 K . The depression in freezing point for 2 molal solution of glucose in the same solvent is 2 K . The relation between K b and K f is:
Options
- AK b = 2   K f
- BK b = 1 .5   K f
- CK b = K f
- DK b = 0 .5   K f
Correct answer
A. K b = 2   K f
Step-by-step solution
Freezing point depression refers to the lowering of the freezing point of solvent upon the addition of solute. Boiling point elevation refers to the increase in the boiling point of a solvent upon the addition of a solute. ∆ T b = iK b m ⇒ 2 = iK b × 1 . . . . . . . . . . . . i ∆ T f = iK f m ⇒ 2 = iK f × 2 . . . . . . . . . . . . . . . ii Dividing i ii , 1 = K b 2 K f K b = 2   K f