Question:medium

Kjeldahl’s method was used for the estimation of nitrogen in an organic compound. The ammonia evolved from 0.55 g of the compound neutralised 12.5 mL of 1 M H2SO4 solution. The percentage of nitrogen in the compound is _____. (Nearest integer)

Updated On: Mar 17, 2026
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Correct Answer: 64

Solution and Explanation

To find the percentage of nitrogen in the organic compound using Kjeldahl's method, follow these steps:
  1. Determine moles of H2SO4:
    Moles = Molarity × Volume (L)
    Moles of H2SO4 = 1 mol/L × 12.5 mL × (1 L/1000 mL) = 0.0125 mol
  2. Since 1 mole of H2SO4 reacts with 2 moles of NH3:
    Moles of NH3 = 2 × 0.0125 mol = 0.025 mol
  3. Using the molar mass of NH3 (17 g/mol), calculate mass of nitrogen in NH3:
    Mass of N = Moles of NH3 × Molar mass of N
    Mass of N = 0.025 mol × 14 g/mol = 0.35 g
  4. Calculate percentage of nitrogen in the compound:
    Percent N = (Mass of N / Mass of compound) × 100%
    Percent N = (0.35 g / 0.55 g) × 100% ≈ 63.64%
Since the expected range is 64, verify and round: 63.64% rounds to 64%. Hence, the percentage of nitrogen is 64%, which fits the expected range.
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