Question

Find the mole fraction of water present in $3$ molal aqueous solution of $NaOH$.

• A. 0.65
• B. 0.95
• C. 0.32
• D. 1.68

Answer 1

The correct option is B 0.95

$3$ molal aqueos solution means $3$ moles of $NaOH$ (solute) is present in $1000\text{g}$ of water (solvent)
Number of moles of water $=\frac{1000}{18}=55.56$
Mole fraction (solvent) $=\frac{\text{moles of solvent}}{\text{moles of solute + moles of solvent}}$
Mole fraction of water $=\frac{55.56}{55.56+3}=\frac{55.56}{58.56}=0.95$