Q.
Nitrobenzene is formed as the major product along with aminor product in the reaction of benzene with a hot mixtureof nitric acid and sulphuric acid. The minor product consists of carbon : $42.86\%$, hydrogen : $2.40\%$, nitrogen : $16.67\%$ and oxygen : $38.07\%$,
(i) Calculate the empirical formula of the minor product.
(ii) When $5.5 \,g$ of the minor product is dissolved in $45 \,g$ ofbenzene, the boiling point of the solution is $1,84^{\circ}C$ higherthan that of pure benzene. Calculate the molar mass of theminor product then determine its molecular and structuralformula. (Molal boiling point elevation constant of benzene is $2.53 \,K. \,kg\, mol^{-1})$.
IIT JEEIIT JEE 1999Solutions
Solution:
(i) Empirical formula determination
Elements
C
H
N
O
Weight %
42.86
2.40
16.67
38.07
Moles
3.57
2.40
1.19
2.38
Simplest ratio
3
2
1
2
$\Rightarrow$ Empirical formula $= C _{3} H _{2} NO _{2}$
(ii) $\Delta T_{b}=1.84=2.53 \times \frac{5.5}{M} \times \frac{1000}{45} $
$\Rightarrow M=168$
$\because$ Empirical formula weight $(84) $ is half of molar mass, molecular formula is $C _{6} H _{4} N _{2} O _{4}$ a dinitrobenzene :
| Elements | C | H | N | O |
|---|---|---|---|---|
| Weight % | 42.86 | 2.40 | 16.67 | 38.07 |
| Moles | 3.57 | 2.40 | 1.19 | 2.38 |
| Simplest ratio | 3 | 2 | 1 | 2 |
