In the estimation of nitrogen by Kjeldahl's method, 2.8 g of an organic compound required 20 millimoles of `H_(2)SO_(4)` for the complete neutralisation of `NH_(3)` gas evolved. The percentage of nitrogen in the sample is

Options

A. `20%`
B. `10%`
C. `40%`
D. `30%`

Explanation

To solve the problem of estimating the percentage of nitrogen in an organic compound using Kjeldahl's method, we can follow these steps:

### Step 1: Understand the given data
We are given:
- Mass of the organic compound = 2.8 g
- Millimoles of H₂SO₄ used = 20 mmol

### Step 2: Calculate the milliequivalents of H₂SO₄
The milliequivalents of H₂SO₄ can be calculated using the formula:
\[ \text{Milliequivalents} = \text{Millimoles} \times n \text{-factor} \]
For H₂SO₄, the n-factor is 2 (since it can donate two protons). Therefore:
\[ \text{Milliequivalents of H₂SO₄} = 20 \, \text{mmol} \times 2 = 40 \, \text{milliequivalents} \]

### Step 3: Use the formula for percentage of nitrogen
The formula for calculating the percentage of nitrogen (N) in the organic compound is:
\[ \text{Percentage of N} = \frac{1.4 \times \text{milliequivalents of H₂SO₄}}{\text{weight of organic compound}} \times 100 \]
Substituting the values we have:
\[ \text{Percentage of N} = \frac{1.4 \times 40}{2.8} \times 100 \]

### Step 4: Perform the calculation
Calculating the numerator:
\[ 1.4 \times 40 = 56 \]
Now, substituting back into the formula:
\[ \text{Percentage of N} = \frac{56}{2.8} \times 100 \]
Calculating \( \frac{56}{2.8} \):
\[ \frac{56}{2.8} = 20 \]
Thus:
\[ \text{Percentage of N} = 20 \times 100 = 20\% \]

### Final Answer
The percentage of nitrogen in the sample is **20%**.

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