Question

A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 mL of 0.5 M H₂SO₄. 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

Given that, total mass of organic compound = 0.50 g 

60 mL of 0.5 M solution of NaOH was required by residual acid for neutralisation. 

60 mL of 0.5 M NaOH solution =60/2mL of 0.5M  H₂SO₄ = 30 mL of 0.5 M H₂SO₄ 

Acid consumed in absorption of evolved ammonia is (50–30) mL = 20 mL 

Again, 20 mL of 0.5 MH₂SO₄ = 40 mL of 0.5 MNH₃ 

Also, since 1000 mL of 1 MNH₃ contains 14 g of nitrogen, 

40 mL of 0.5 M NH₃ will contain (14X40/1000)XO.5 = 0.28 g of N 

Therefore, percentage of nitrogen in 0.50 g of organic compound  =(0.28/0.50)X100=56.%