Question

The mole fraction of a solute in its one molal aqueous solution is:

• A. 0.018
• B. 0.027
• C. 0.036
• D. 0.048

Answer 1

Answer: (A)

$w=1000g\left(H_{2}O\right);n$ (solute) $=1mol$
(as $1$ molal aqueous solution implies $1$ mol of solute in $1kg$ of water)
$N$ (water) $=\frac{W}{M}=\frac{1000}{18}=55.55$
Whereas
$n=$ number of moles of solute
$N=$ number of moles of water $\left({\left(\text{H}\right)}_{\text{2}}\text{O}\right)$
$X_{\text{solute}}=\frac{n}{n+N}=\frac{1}{1+55.55}$
$=0.018$