Question

If the mole fraction of acetone in heptane is $0.25$, and its density is $0.895\text{g/mL}$ then what will be the molarity of the solution?

• A. 0.25 M
• B. 2.5 M
• C. 2 M
• D. 0.2 M

Answer 1

The correct option is B 2.5 M

Assuming total moles of the solvent = 1
moles of acetone = 0.25
molar mass of acetone = 58 g/mol
mass of acetone = 14.5
moles of heptane = 0.75
molar mass of heptane = 100 g/mol
mass of heptane = 75 g/mol
Total mass of the solution = 89.5 g
Volume of the solution = $\frac{\text{mass}}{\text{density}}=\frac{89.5}{0.895}=100$ mL
$\text{Molarity}=\frac{\text{moles}}{\text{volume(L)}}=\frac{0.25}{0.1}=2.5\text{M}$