AIIMS 2007
- Exam
- AIIMS
- Year
- 2007
- Subject
- Chemistry
- Chapter
- Solutions
AIIMS 2007 · Chemistry · Solutions
The vapour pressure of pure benzene at a certain temperature is...
The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, nonelectrolyte solid weighing (0.5 ) is added to 39.0 () of benzene (molar mass (78 / ) ). The vapour pressure of the solution then is 0.845 bar. What is the molecular mass of the solid substance?
Options
- A58
- B180
- C170
- D145
Correct answer
C. 170
Step-by-step solution
(P_A^{\circ}=0.850) bar, bar
(w=0.5 \mathrm{ g}, \quad m=\text{ ? })
weight of solvent (benzene) (=39.0 \mathrm{ g})
and molecular weight of benzene (=78 \mathrm{ g})
As we know, (\frac{P_A^{\circ}-P_S}{P_A^{\circ}}=x_B=\frac{n_B}{n_A})
(\frac{0.850-0.845}{0.850}=\frac{\frac{w_B}{M_B}}{\frac{w_A}{M_A}}=\frac{\frac{0.5}{m}}{\frac{39}{78}})
On solving, we get molecular mass of solid structure ((\mathrm{m})=170 \mathrm{ g}).