Question

The depression in the freezing point of a sugar solution was found to be 0.402°C. Calculate the osmotic pressure of the sugar solution at 27°C. (K_f = 1.85 K kg mol⁻¹)

Answer 1

Given: R = 0.0821 L atm mol⁻¹ K⁻¹

T = 27°C = 300 K

K_f = 1.85 K kg mol⁻¹

ΔT_f = 0.402°C

We know that

ΔT_f = K_f m 

`m = (Delta T_f)/K_f`

= `0.402/1.85`

= 0.2173 mol/kg

Let 1 kg of solvent = 1 L of solution, so

C = m

= 0.2173 mol/L

By using van’t Hoff equation

π = CRT

π = 0.2173 × 0.0821 × 300

π = 5.35 atm