Question

A solution X is prepared by dissolving three moles of glucose in one litre of water and a solution Y is prepared by dissolving 1.5 moles of sodium chloride in one litre of water. Will the osmotic pressure of X be higher, lower or equal to that of Y? Give a reason for your answer.

Answer 1

The osmotic pressure will be same for both solutions. Both solutions are isotonic.
The osmotic pressure $\pi =iCRT$, where i is the vant Hoff factor and C is the molar concentration.
For solution $X$, $i=1$ as glucose is non electrolyte and does not dissociate and $C=\frac{3mol}{1L}=3M$
Hence, the osmotic pressure
$\pi =iCRT=1\times 3\times RT=3RT$
For solution Y, $i=2$ as NaCl is strong electrolyte and dissociates into ions and $C=\frac{1.5mol}{1L}=1.5M$
Hence, the osmotic pressure
$\pi =iCRT=2\times 1.5\times RT=3RT$