The Kjeldahl Method and Nitrogen Estimation

The Kjeldahl method is a widely used technique for the estimation of nitrogen in organic compounds. It involves the digestion of the compound and the subsequent determination of the nitrogen content by titration. In this method, the organic compound is digested with concentrated sulfuric acid, which converts the nitrogen present in the compound into ammonium sulfate.

The Given Information

In this problem, we are given that 1.4 g of an organic compound was digested by the Kjeldahl method. The evolved ammonia from the digestion was absorbed in 60 mL of M/10 sulfuric acid. We are also given that the unreacted sulfuric acid required 20 mL of M/10 sodium hydroxide for complete neutralization.

Calculating the Amount of Ammonia Produced

To calculate the amount of ammonia produced, we need to determine the number of moles of sulfuric acid neutralized by the ammonia. Since we know the volume and concentration of the sulfuric acid and sodium hydroxide, we can use the following equation:

Moles of acid = Concentration of acid × Volume of acid

Moles of base = Concentration of base × Volume of base

Since the reaction between sulfuric acid and sodium hydroxide is 1:2, the moles of acid neutralized by the base will be twice the moles of base used. Therefore, the moles of acid neutralized by ammonia can be calculated as follows:

Moles of acid neutralized by ammonia = 2 × Moles of base

Calculating the Nitrogen Content

The moles of acid neutralized by ammonia are equivalent to the moles of ammonia produced during the digestion of the organic compound. Since 1 mole of ammonia contains 1 mole of nitrogen, we can calculate the moles of nitrogen as follows:

Moles of nitrogen = Moles of ammonia

To calculate the percentage of nitrogen in the compound, we divide the moles of nitrogen by the mass of the compound and multiply by 100:

Percentage of nitrogen = (Moles of nitrogen / Mass of compound) × 100

Solving the Problem

In this problem, we are given that 1.4 g of the organic compound was digested. From the given information, we can calculate the moles of nitrogen produced and then determine the percentage of nitrogen in the compound.

Using the given information, we can calculate the moles of acid neutralized by ammonia:

Moles of acid neutralized by ammonia = 2 × (M/10) × 0.020 L

Next, we can calculate the moles of nitrogen:

Moles of nitrogen = Moles of acid neutralized by ammonia

Finally, we can calculate the percentage of nitrogen in the compound:

Percentage of nitrogen = (Moles of nitrogen / 1.4 g) × 100

By performing the calculations, we find that the percentage of nitrogen in the compound is 10%.

Therefore, the correct answer is option 'B' - 10%.