Question

Molality of pure liquid benzene ($C_6{H}_6$) if its density d=1.2 g/ml is:

• A. $0.83m$
• B. $50m$
• C. $0.7m$
• D. $12.8m$

Answer 1

The correct option is D $12.8m$

We know that molality $=\frac{moleofsolute}{weightofsolventinkg}$

Now the solution is purely of benzene,

Let x kg be the weight of the solution. Then, 1000x g benzene is there in the solution.

Therefore, moles of benzene $=\frac{1000x}{78}$ (since molar mass of benzene is 78g)

Therefore, molality $=\frac{1000x}{78\times x}$ $=\frac{1000}{78}$ $=12.8m$

Hence, (d) is the correct option.