JEE Main 2017 · Chemistry · Qualitative and Practical Chemistry · easy

In Kjeldahl's method, the ammonia evolved from 0.40 g of an organic compound is absorbed in 50 mL of 0.50 N H2SO4. The excess acid requires 30 mL of…

Single correct option

In Kjeldahl's method, the ammonia evolved from

0.40\ \mathrm{g}

of an organic compound is absorbed in

50\ \mathrm{mL}

0.50\ \mathrm{N\ H_2SO_4}

. The excess acid requires

30\ \mathrm{mL}

0.50\ \mathrm{N\ NaOH}

for neutralisation. The percentage of nitrogen in the compound is

Show answer and solution

Answer: (D) $35\%$

Acid taken

=50\times0.50=25

meq. Excess acid

=30\times0.50=15

meq. Acid used by

\mathrm{NH_3}=25-15=10

meq, which is

10

meq of

\mathrm{NH_3}=10

mmol of N

=140

mg. Percentage

\mathrm{N}=\dfrac{140\ \mathrm{mg}}{400\ \mathrm{mg}}\times100=35\%

. Forgetting to subtract the back-titrated excess acid gives

87.5\%

, and using eq. wt. of N as

28

gives

70\%

Original question written in the JEE Main 2017 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake