Question

During estimation of nitrogen present in an organic compound by Kjeldahl's method, the ammonia evolved from 2 g of an organic compound was neutralized by 20 ml of 0.8 M H2SO4 solution. The percentage of nitrogen present in the compound is:

(a) 4%
(b) 8%
(c) 12%
(d) 16%

Answer 1

To find the percentage of nitrogen in the organic compound, the moles of H₂SO₄ used in the reaction are first calculated. These are then used to determine the moles of NH₃ and, consequently, the nitrogen. However, the calculated percentage of nitrogen does not match any of the provided options, indicating an error in the question or options.

Step-by-step explanation:

To calculate the percentage of nitrogen in the organic compound using Kjeldahl's method, we need to know the moles of H2SO4 that reacted with the ammonia (NH3), which comes from the nitrogen in the organic compound:

1. First, we determine the moles of H2SO4. The molarity of H2SO4 is 0.8 M and the volume used is 20 mL or 0.020 L. Moles of H2SO4 = Molarity × Volume = 0.8 mol/L × 0.020 L = 0.016 moles.
2. In the reaction, each mole of H2SO4 reacts with two moles of NH3. So, moles of NH3 = 2 × moles of H2SO4 = 2 × 0.016 = 0.032 moles.
3. Since the molar mass of nitrogen (N) is 14.01 g/mol, mass of N in the compound = moles of N × molar mass of N = 0.032 moles × 14.01 g/mol = 0.44832 g.
4. Finally, the percentage of nitrogen in the compound = (mass of N / mass of the compound) × 100 = (0.44832 g / 2 g) × 100 = 22.416%, which is not among the given options, indicating that there may be an error in the statement of the question or the options provided.

The correct calculation method is shown above, but the result does not match any of the options (a) 4%, (b) 8%, (c) 12%, (d) 16%. The percentage calculated is significantly higher than all given options. This might suggest there has been a typo in the question or the options provided.