Question

What amount of ethanol(assumed on-volatile) must be dissolved in 1kg water so that it freezes at -2° C.

[Given Freezing point of water = 0°C

K_{f =} 1.86 K kg/mol]

Answer 1

Given, K_f = 1.86 k kg/mol

ΔT_f = 2°C or 2k

ΔT_f = k_fm

Let say x gm ethanol dissolved in 1kg water.

∴ ΔT_f = k_f = \(\frac{x}{\frac{46}{1}}\)

⇒ 2 = 1.86 x \(\frac{x}{46}\)

⇒ \(\frac{2\times46}{1.86}=x\)

⇒ x = 49.46 g