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NCERT Class XII Chemistry
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Question : 41 of 53
Marks: +1, -0
Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K2SO4K_2SO_4 in 2 litre of water at 25°C, assuming that it is completely dissociated.
Solution:  
 K2 SO4\ {K}_{2} \ {SO}_{4} dissolved =25 mg=0.025g=25 \ {mg}=0.025 {g}
Volume of solution =2 L,    T=25∘ C=298 K=2\,{L},\;\; T=25^{\circ}\,{C}=298\,{K}
Molar mass of  K2SO4=2×39+32+4×16\ {K}_{2} {SO}_{4}=2 ×39+32+4 ×16
=174 gmol−1=174 \ {g} {mol}^{-1}
 K2SO4\ {K}_{2} {SO}_{4} dissociates completely as,  K2 SO4rightarrow2K++ SO42−\ {K}_{2} \ {SO}_{4} \\rightarrow2 {K}^{+}+\ {SO}_{4}^{2-}
i.e., ions produced =3,∴  i=3=3, ∴\; i=3
∴  π=iCRT=ihVRT\therefore\; \pi = i C R T = i \frac{h}{V} R T
=i×w/M×1VRT=i ×{w}/{M} ×{1}{V} R T
=3×0.025g174gmol−1×12L×0.0821LatmK−1mol−1×298K=3 \times \frac{0.025 {g}}{174 {g} {mol}^{-1}} \times \frac{1}{2 {L}} \times 0.0821 {L} atm {K}^{-1} {mol}^{-1} \times 298 {K}
=5.27×10−3 atm=5.27× 10^{-3} \ {atm}
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