0.45 gm of an organic compound gave on combustion 0.792 gm of CO₂ and 0.324 gm of water. 0.24 gm of the same substance was Kjeldahlised and the ammonia liberated was absorbed in 50.0 ml of M/8 H₂SO₄. The excess acid required 77.0 ml of N/10 NaOH for complete neutralisation. Calculate the empirical formula of the compound.

Calculation of the percentage composition :

i)  Percentage of carbon

                        $=\frac{12}{44}\times \frac{{\text{Mass of CO}}_2\text{Produced}}{\text{Mass of substance taken}}\times 100$

                        $=\frac{12}{44}\times \frac{0\text{.}792}{0\text{.}45}\times 100=48\text{.}0$

ii)  Percentage of hydrogen

                           $=\frac{2}{18}\times \frac{{\text{Mass of H}}_2\text{O produced}}{\text{Mass of substance taken}}\times 100$

                          $=\frac{2}{18}\times \frac{0\text{.}324}{0\text{.}45}\times 100=8\text{.}0$

iii)  Percentage of nitrogen

mEq. of H₂SO₄ $=50\times \frac{\text{M}}{8}\times 2=12\text{.}5$

mEq. of NaOH $=72\times \frac{1}{10}\times 1=7\text{.}7$

Excess of H₂SO₄ used to neutralise ammonia

                       = 12.5 - 7.7 = 4.8

Percentage of N₂ $=\frac{1\text{.}4\times 4\text{.}8}{0\text{.}24}=28\text{.}0\text{\%}$

iv)  Percentage of oxygen = 100 - (percentage of C + percentage of H + percentage of N) = 100 - (48.0 + 8.0 + 28.0) = 16.0.

b.  Calculation of empirical formula :

 

Hence, the empirical formula of the compound is C₄H₈N₂O.