Question

The mole fraction of benzene in a solution containing 39% by mass in an organic solvent of molecular mass 122 is

• A. 0.5
• B. 0.6
• C. 0.4
• D. 0.35

Answer 1

Answer: (A)

0.5

Answer 2

Mass of benzene $(w_2) = 39 \,g$
Mass of solvent $(w1) = 61 \,g$
Molecular mass of benzene $(M_2) = { 78\, g\, mol^{-1}}$
Molecular mass of solvent $(M_1) = {122\, g\, mol^{-1}}$Mole fraction of benzene, $x_2$
$= \frac{w_{2}/ M_{2}}{w_{1} /M_{1} +w_{2} /M_{2}}$
$= \frac{39 /78 }{61/ 122 + 39 /78} = \frac{0.5}{0.5 +0.5} =0.5$