Question

In a solution of 7.8 gm benzene $C_6{H}_6$ and 46.0 gm toluene $\left(C_6{H}_5{CH}_3\right)$, the mole fraction of benzene in this solution is:

• A. 1/6
• B. 1/5
• C. 1/2
• D. 1/3

Answer 1

Answer: (A)

1/6

• Mole fraction is a unit of concentration, defined to be equal to the number of moles of a component divided by the total number of moles of a solution.
  
• Because it is a ratio, mole fraction is a unitless expression. The mole fraction of all components of a solution, when added together, will equal 1.
  
• We know No. of moles=$\frac{Given-mass}{Molar-mass}$

Molar mass of Benzene=78

Molar mass of Toluene=92

Hence, No. of mole of Benzene=$\frac{7.8}{78}$= 0.1 moles

No. of moles of toluene=$\frac{46}{92}$= 0.5 moles

So, Mole fraction of Benzene=$\frac{0.1}{0.5+0.1}$=$\frac{1}{6}$

• Hence, A is correct answer.