Question

During the experiment you are given 2.5 m acetone solution in heptane (molar mass = 100 g/mol) having a density of 0.5 g/mL. Find the mole fraction of solute.

• A. 0.3
• B. 0.2
• C. 0.85
• D. 0.02

Answer 1

The correct option is B 0.2

Let us assume the weight of the solvent as 1 kg or 1000 g.
$\text{Molality}\left(m\right)=\frac{\text{Moles of solute}}{\text{Weight of solvent (kg)}}$
Moles of acetone (solute) = 2.5 moles
Moles of solvent $\left(\text{heptane}\right)=\frac{1000}{100}=10$ mol
$\text{Mole fraction of solute}=\frac{\text{Moles of solute}}{\text{Total moles}}=\frac{2.5}{(2.5+10)}=\frac{2.5}{12.5}=0.2$