Q20 of 30 Page 1

Determine the osmotic pressure of a solution prepared by dissolving 2.5 × 10–2 g of K2SO4 in 2L of water at 25°C, assuming that it is completely dissociated.

(R =0.0821 L atm K–1mol–1, Molar mass of K2SO4= 174gmol-1)


When K2SO4 dissociates,



The number of ions produced are = 2+1 = 3


∴ Vant Hoff’s factor i = 3


To calculate osmotic pressure, we know,



[As, n = ]


Here, π is the osmotic pressure


n = Number of moles of solute


w = Weight of solute


M = Molecular mass of solute


R = Gas constant


t = Temperature


From the question,


w = 0.025gm


Volume V = 2L


t = 298 K


R =0.0821 L atm K–1mol–1


M = 174gm mol-1


∴ Putting all the values,



So, osmotic pressure is


π = 5.27 × 10-3 atm.


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