Question

Calculate the mole fraction of 30% by mass benzene in a solution with carbon tetrachloride.

• A. 0.542
• B. 0.458
• C. 0.518
• D. 0.324

Answer 1

The correct option is B 0.458

Let total mass of the solution = 100 g
mass of benzene = 30 g
Mass of $CC{l}_4$ = total mass – mass of benzene = 100 – 30 = 70 g
Molar mass of benzene$\left(C_6{H}_6\right)$ = $6\times 12+6\times 1=78$ g/mole
Number of Moles = $\frac{\text{given mass}}{\text{molar mass}}$
Number of moles of $C_6{H}_6$
$=\frac{30}{78}=0.3846$ mol
Molar mass of $CC{l}_4=1\times 12+4\times 35.5=154$ g/mole
Number of moles of $CC{l}_4=\frac{70}{154}=0.4545$ mol
Use the formula of mole fraction
Mole Fraction = $\frac{\text{Moles of benezene}}{\text{total moles in the solution}}=\frac{0.3846}{0.3846+0.4545}=0.458$