Question

The molality of a solution of acetone in heptane is 2.5 m. The mole fraction of acetone is:

Answer 1

Assuming 1 kg of the solvent, 2.5 m solution has 2.5 mole of the acetone in 1 kg of heptane.
Mass of the solvent = 1 kg
Moles of the solute = 2.5 mol
Molar mass of heptane $\left(C_7{H}_{16}\right)$ = 100 g/mol
$\text{Moles of the solvent}=\frac{1000}{100}=10mol$
Mole fraction of acetone $=\frac{\text{moles of acetone}}{\text{total moles of solute and solvent}}=\frac{2.5}{12.5}=0.2$