In a Kjeldahl estimation, 0.750 g of an organic compound was digested and the ammonia evolved was absorbed in 40.0 mL of 0.250 M H2SO4. The excess acid required 49.0 mL of 0.200 M NaOH for neutralisation. Using N = 14, find the percentage of nitrogen in the compound (two decimals).

JEE Advanced levelNumerical answerDifficulty 3 of 3si198

In a Kjeldahl estimation, 0.750 g of an organic compound was digested and the ammonia evolved was absorbed in 40.0 mL of 0.250 M $H X_{2} SO X_{4}$ . The excess acid required 49.0 mL of 0.200 M NaOH for neutralisation. Using N = 14, find the percentage of nitrogen in the compound (two decimals).

Numerical answer type, answer in %, tolerance 0.02.

Total

H X^{+}

taken = 40.0 x 0.250 x 2 = 20.0 mmol;

H X^{+}

left over = 49.0 x 0.200 = 9.8 mmol. Acid used by ammonia = 10.2 mmol, so

NH X_{3}

= 10.2 mmol and N = 10.2 x 14 = 142.8 mg. %N =

\frac{142.8}{750} \times 100 = 19.04%