Question

A sample of 0.50 g of an organic compound was treated according to Kjeldahls method. The ammonia evolved was absorbed in 50 ml of 0.5$M{H}_{2}S{O}_4$. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.

Answer 1

Total mass of orgasmic compound is 0.50 g.
Initial volume of 0.5 M sulphuric acid is 50 mL.
The remaining acid required 60 mL of 0.5 M NaOH solution for neutralization.
60 mL of 0.5 M NaOH solution $=\frac{60}{2}=30mL$ of 0.5 M sulphuric aicd solution.
Acid consumed during absorption of ammonia is $50-30=20mL$.
20 mL of 0.5 M sulphuric acid corresponds to 40 mL of 0.5 M ammonia.
1000 mL of 1 M ammonia contains 14 g of nitrogen.
40 mL of 0.5 M ammonia will contain $\frac{14\times 40}{1000}\times 0.5gN$.
Percentage of N $=\frac{14\times 40\times 0.5}{1000\times 0.50}\times 100=56$%