Question

Mole fraction of the solute in a $1.00$ molal aqueous solution is:

• A. $1.7700$
• B. $0.1777$
• C. $0.0177$
• D. $0.0344$

Answer 1

The correct option is C $0.0177$

Molality is number of moles of solute present in $1\text{kg}$ of solvent.
Molar mass of water $\left(H_{2}O\right)=18\text{g/mol}$
Given mass of water $=1000\text{g}=1\text{kg}$

$\text{Moles}=\frac{\text{Given Mass}}{\text{Molecular Mass}}=\frac{1000}{18}=55.5\text{moles}$

$\text{Mole fraction of solute}=\frac{\text{Moles of solute}}{\text{Total moles of solution}}$

$\text{Therefore,}\frac{1}{(55.5+1)}=0.0177$