Question

Arrange the following solutions in the increasing order of their osmotic pressure
(i) $ 34.2 \,g/L $ sucrose $ (M = 342) $
(ii) $ 60 \,g/L $ urea $ (M = 60) $
(ii) $ 90 \,g/L $ glucose $ (M = 180) $
(vi) $ 58.5\, g/L\, NaCl (M = 58.5) $

• A. Sucrose < Urea < Glucose < NaCl
• B. Sucrose < Glucose < NaCl < Urea
• C. Sucrose < Glucose < Urea < NaCl
• D. NaCl < Urea < Glucose < Sucrose

Answer 1

Answer: (C)

Osmotic pressure is a colligative property, the property of the solution which depends only on the number of solute particles.
$(i) 34.2 \,g/ L$ sucrose $= 0.1$ mole sucrose in $1 \,L$ solution
$(ii) 60 \,g/L$ urea $= 1$ mole urea in $1 \,L$ solution.
$(iii) 90 \,g/L$ glucose $= 0.5$ mole glucose in $1\, L$ solution.
$(vi) 58.5 \,g/L \,NaCl = 1 \,mol \,NaCl$ in $1\,L$ solution
Sucrose, urea and glucose do not dissociate into their ions while $1$ mole $NaCl$ gives $2$ mole particles i.e., $Na^+$ and $Cl^-$ ions.
Hence, the correct increasing order of their osmotic pressure is sucrose < glucose < urea < $NaCl$. Solutions.