See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Concept: Kjeldahl's method is a classical analytical technique used to determine the nitrogen content in organic compounds. Step 1: In Kjeldahl's method, the organic compound is first digested with concentrated H2SO4, which converts the nitrogen present in the compound into ammonium sulphate, (NH4)2SO4. Step 2: The ammonium sulphate is then treated with excess NaOH solution and heated, which releases ammonia gas (NH3). Step 3: The ammonia gas evolved is absorbed in a known volume of standard acid (usually H2SO4 or HCl). Step 4: The amount of acid neutralized by NH3 is determined by back titration with standard NaOH. Step 5: From the volume of acid neutralized, the amount of NH3 and hence the amount of nitrogen in the original compound is calculated. Thus, nitrogen is estimated in the form of NH3. Why other options fail: (a) N2 - nitrogen is not liberated as elemental nitrogen gas in this method. (c) NO2 - nitrogen dioxide is not formed in this method. (d) none of these - incorrect since NH3 is indeed the form in which nitrogen is estimated. Therefore, the correct answer is B.