Thursday, May 2, 2013

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 K2SO4in 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+  +  SO42-
 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

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