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 neutralization. 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 neutralization.

60 mL of 0.5 M NaOH solution \(=\frac{60}{2}\) ML of 0.5 M 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 \(\frac{14×40}{1000}×0.5= 0.28\) g of N

Therefore, the percentage of nitrogen in 0.50 g of organic compound \(-\frac{0.28}{0.50}×100= 56%\)%