Find the molarity of the 5 molal urea solution, whose density is $1.3 \mathrm{~g} / \mathrm{mL}$ (given,…
Find the molarity of the 5 molal urea solution, whose density is $1.3 \mathrm{~g} / \mathrm{mL}$ (given, molecular weight of urea is $60.06 \mathrm{~g} / \mathrm{mol}$ )
$>5 \mathrm{M}$
$=5 \mathrm{M}$
$ < 5 \mathrm{M}$
Can't be predicted
Solution
5 molal urea solution $(d=1.3 \mathrm{~g} / \mathrm{mL})$
$1 \mathrm{~kg}$ of solvent contains 5 moles of urea. Means $1000 \mathrm{~g}$ water contains $300 \mathrm{~g}$ of urea. Molarity of $1300 \mathrm{~g}$ urea solution contains $300 \mathrm{~g}$ urea will be
$
M_{\text {urea }}=\frac{\left(\frac{300}{60}\right) \times 1000}{\left(\frac{1300}{1.3}\right)}=5.0
$
Hence, the correct option is (2)