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)

Mass of benzene $\left(w_2\right)=39g$
Mass of solvent $(w1)=61g$
Molecular mass of benzene $\left(M_2\right)=78gmo{l}^{-1}$
Molecular mass of solvent $\left(M_1\right)=122gmo{l}^{-1}$
Mole fraction of benzene, $x_2$
$=\frac{w_2/M_2}{w_1/M_1+w_2/M_2}$
$=\frac{39/78}{61/122+39/78}=\frac{0.5}{0.5+0.5}=0.5$