Question

0.303 g of an organic compound was analysed for nitrogen by Kjeldahl’s method. The ammonia gas evolved was absorbed in 50 ml of 0.1N-H2SO4. The excess acid required 25 ml of 0.1 N NaOH for neutralization. The percentage of nitrogen in the given compound is

Answer 1

Your problem is same as the problem below

Thinking process This problem is based on the estimation of percentage fo N in organic compound using Kjeldhl's method Use the concept of stoichiometry and follow the steps given below to solve the problem.
(a) Write the balanced chemical reaction for the conversion of N present in organic compound to ammonia, ammonia to ammonium sulphate and ammonium sulphate to sodium sulphate.
(b) Calculate millimoles (m moles) of N present in organic compound followed by mass of N present in organic compound using the concept of stoichiometry.
(c) At last, calculate % of N present in organic compound using formula
Mass of organic compound = 1.4 g
Let it contain x m mole of N atom.
Organic compound →NH3(x m mole)
2NH3+H2SO4(6 m moleinitiall) ytaken→(NH4)2SO4
H2SO4+2NaOH→Na2SO4+2H2O
2 m mole NaOH reacted.
Hence, m moles of H2SO4reacted from Eq. (ii) = 1
⇒ m moles of H2SO4 reacted from Eq. (i) = 6 - 1 = 5 m moles
⇒ m moles of NH3 in Eq. (i) = 2 × 5 = 10 m moles
⇒ m moles of N atom in the organic compound = 10 m moles
⇒ Mass of N=10×(10^−3) ×14=0.14g