Question

$1.4g$ of an organic compound was digested according to Kjeldahl's method and the ammonia evolved was absorbed in $60mL$ of $M/10H_{2}S{O}_4$ solution. The excess sulphuric acid required $20mL$ of $M/10NaOH$ solution for neutralization. The percentage of nitrogen in the compound is :

• A. 3
• B. 5
• C. 10
• D. 24

Answer 1

Answer: (C)

Out of $60mL$ of $\frac{M}{10}{H}_{2}S{O}_4,10mL$ will be neutralized with $20mL$ of $\frac{M}{10}NaOH$.
Hence, $60-10=50mL$ of $\frac{M}{10}{H}_{2}S{O}_4$ will be neutralized with ammonia. This will be equal to $100mL$ ammonia.
$1000mL$ of $1M$ ammonia corresponds to $14g$.
$100mL$ of $\frac{M}{10}$ ammonia will correspond to $\frac{100}{1000}\times \frac{1}{10}\times 14=0.14g$ nitrogen
Thus, $1.4g$ of organic compound contains $0.14g$ nitrogen.
Hence, $100g$ of organic compound will contain $\frac{0.14}{1.4}\times 100=10g$ nitrogen
Hence, the per cent of nitrogen in the organic compound is $10\%$.