Chemistry - Liquid Solution Question with Solution | TestHub

A $1$ molal solution of glucose means $1$ mole of glucose is dissolved in $1000$ g of water.

Number of moles of solute (glucose), $n=1$ mol

Number of moles of solvent (water), $N=\frac{1000}{18}=55.55$ mol

According to Raoult's law, the relative lowering of vapor pressure is equal to the mole fraction of the solute.

$\frac{\Delta P}{P^{\circ }}={\chi }_{\text{solute}}=\frac{n}{n+N}$

$\frac{\Delta P}{P^{\circ }}=\frac{1}{1+55.55}=\frac{1}{56.55}$

$\frac{\Delta P}{P^{\circ }}\approx 0.01768\approx 1.8\times 10^{-2}$

Answer: $1.8\times 10^{-2}$