Question

q-An aqueous solution of urea (NH2CONH2) is 3.0 molal. find out the mole fraction of the urea thanks in advance

Answer 1

Moles of urea , m=3
Mass of water=1000 g
so,moles of water , m°=1000/18
Mole fraction of urea=m/(m+m°)
you can solve it by substituting the values.
Hope it helps.:-)

Answer 2

Mole fraction of urea is 0.051 m

Solution:

3.0 molar solution contains 3 moles of urea per 1000g (1kg) of water.

Molar mass of water = 18 g/mol

Moles of water= $\frac{\text {Mass of water }}{\text { molar mass of water }}=\frac{1000}{18 \mathrm{g} / \mathrm{mol}}=55.402$

For 1kg of solvent here are 3 moles of urea which has mass of

$3 \text { moles } \times 60 \frac{\mathrm{g}}{\mathrm{mol}}=180 \mathrm{g}$

$3 \text { moles } \times 60 \frac{\mathrm{g}}{\mathrm{mol}}=180 \mathrm{g}$

$=\frac{\text { Number of moles of urea }}{\text { Number of moles of urea }+\text { number moles of water }}$

$=\frac{3}{3+55.402}=\frac{3}{58.402}=0.051 \mathrm{m}$