Question

A solution contains 0.8960 g K₂SO₄ in 500 mL solution. Its osmotic pressure is found to be 0.690 atm at 27°C. Calculate the value of van’t Hoff factor.

Answer 1

Given: Mass of K₂SO₄ = 0.8960 g

Volume of solution (V) = 500 mL = 0.5 

Temperature (T) = 27°C = 300 K

Observed osmotic pressure `pi_"obs"` = 0.690 atm

Molar mass of K₂SO₄ = 39.1 × 2 + 32.1 + 16 × 4 = 174.3 g/mol

Gas constant (R) = 0.0821 J K⁻¹ mol⁻¹

Moles of K₂SO₄ = `0.8960/174.3`

= 0.00514 mol

Let no. of dissociation (i) = 1

`pi_"theory" = CRT`

= `0.00514/0.5 xx 0.0821 xx 300`

= 0.01028 × 24.63

= 0.253 atm

Van’t Hoff factor (i) = `pi_"obs"/pi_"theory"`

= `0.690/0.253`

= 2.72