In Kjeldahl's method, nitrogen in the compound is converted to NH₃.
The ammonia is absorbed and reacts with H₂SO₄ according to: 2NH3+H2SO4→(NH4)2SO4.
Given that 15 mL of 1 M H₂SO₄ was neutralized:
Moles of H₂SO₄ = 15 × 10⁻³ mol.
From stoichiometry, 1 mol H₂SO₄ reacts with 2 mol NH₃.
Therefore, moles of NH₃ = 2 × 15 × 10⁻³ = 0.030 mol.
Since each NH₃ contains 1 nitrogen atom:
Moles of N = 0.030 mol.
Mass of N = 0.030 × 14 = 0.42 g.
Percentage of N in compound = (0.42/1) × 100 = 42%.