Question

Elevation in boiling point for 1.5 molal solution of glucose in water is 4 K The depression in freezing point of 4.5 molal solution of glucose in water is 4 K. The ratio of molal elevation constant to molal depression constant (K_b/K_f) is ______.

Options

• 2 : 0

• 5 : 5

• 1 : 1

• 3 : 1

Answer 1

Elevation in boiling point for 1.5 molal solution of glucose in water is 4 K The depression in freezing point of 4.5 molal solution of glucose in water is 4 K. The ratio of molal elevation constant to molal depression constant (K_b/K_f) is 3 : 1.

Explanation:

ΔT_b = K_bm₁

ΔT_f = K_fm₂

Given, m₁ = 1.5 m

m₂ = 4.5 m

ΔT_b = 4 K

ΔT_f = 4K

Dividing (1) by (2)

`(Δ"T"_"b")/(Δ"T"_"f") = ("K"_"b" "m"_1)/("K"_"f" "m"_2)`

`4/4 = ("K"_"b" xx 1.5)/("K"_"f" xx 4.5)`

`"K"_"b"/"K"_"f" = 4.5/1.5 = 3/1`

So, K_b : K_f = 3 : 1