Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K2SO4 in 2 liter of water at 25° C, assuming that it is completely dissociated.

Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K₂SO₄ in 2 liter of water at 25° C, assuming that it is completely dissociated.

Solution

Given that

Mass of K₂SO₄, w  = 25 mg  = 0.025g  (use 1 g  = 1000 mg ) 

Volume V  = 2 liter

T = 25 + 273  = 298 K (add 273 to convert in Kelvin)

The  reaction of dissociation of K₂SO₄

K2So4  → 2K⁺  +  SO4^2-

 Number if ions produced  = 2+ 1  = 3
So van’t Hoff factor i  = 3

Use the formula of Osmotic pressure 

Gas constant, R = 0.0821 L atm K^-1mol^-1

Molar mass of K₂SO₄ ,M = 2 × 39 + 1 × 32 + 4 × 16 = 174 g mol^-1

Plug the values we get 

π= 5.27 × 10^-3 atm 

Answer

Osmotic pressure = 5.27 × 10 ^{– 3} atm