For the estimation of nitrogen, `1.4 g` of an organic compound was digested by Kjeldahl method and the evolved ammonia was absorbed in `60 mL` of `(M)/(10)` sulphuric acid. The unreacted acid required `20 mL` of `(M)/(10)` sodium hydroxide of complete neutralization. The percentage of nitrogen in the compound is:

Options

A. `6%`
B. `10%`
C. `3%`
D. `5%`

Explanation

To calculate the percentage of nitrogen in the organic compound using the Kjeldahl method, we can follow these steps:

### Step 1: Determine the amount of sulfuric acid used
The total volume of sulfuric acid used is given as 60 mL of \( \frac{M}{10} \) sulfuric acid.

**Calculation:**
- Molarity of sulfuric acid = \( \frac{M}{10} \)
- Volume of sulfuric acid = 60 mL = 0.060 L
- Moles of sulfuric acid = Molarity × Volume = \( \frac{M}{10} \times 0.060 \) L = \( \frac{0.060}{10} \) = 0.006 moles

### Step 2: Calculate the equivalents of sulfuric acid
Since sulfuric acid (H₂SO₄) has two acidic protons, we can calculate the equivalents of sulfuric acid.

**Calculation:**
- Equivalents of H₂SO₄ = Moles × 2 = \( 0.006 \times 2 = 0.012 \) equivalents = 12 milliequivalents

### Step 3: Determine the amount of sodium hydroxide used
The unreacted sulfuric acid required 20 mL of \( \frac{M}{10} \) sodium hydroxide for complete neutralization.

**Calculation:**
- Molarity of sodium hydroxide = \( \frac{M}{10} \)
- Volume of sodium hydroxide = 20 mL = 0.020 L
- Moles of sodium hydroxide = Molarity × Volume = \( \frac{M}{10} \times 0.020 \) L = \( \frac{0.020}{10} \) = 0.002 moles

### Step 4: Calculate the equivalents of sodium hydroxide
Sodium hydroxide (NaOH) has one acidic proton.

**Calculation:**
- Equivalents of NaOH = Moles = 0.002 equivalents = 2 milliequivalents

### Step 5: Calculate the equivalents of sulfuric acid that reacted with ammonia
The equivalents of sulfuric acid that reacted with ammonia can be calculated by subtracting the unreacted equivalents from the total equivalents.

**Calculation:**
- Equivalents of H₂SO₄ used against NH₃ = Total equivalents - Unreacted equivalents = 12 - 2 = 10 milliequivalents

### Step 6: Calculate the percentage of nitrogen in the organic compound
Using the formula for the percentage of nitrogen:
\[ \text{Percentage of N} = \left( \frac{\text{mass of compound}}{\text{mass of nitrogen in equivalents}} \right) \times 100 \]
The mass of nitrogen can be calculated from the equivalents of sulfuric acid that reacted with ammonia.

**Calculation:**
- Since 1 equivalent of nitrogen corresponds to 1 equivalent of H₂SO₄, we have 10 milliequivalents of nitrogen.
- Therefore, mass of nitrogen = 10 milliequivalents = 10 mg (since 1 equivalent of nitrogen = 1 g)
- Percentage of N = \( \frac{1.4 \, \text{g} \times 10}{1.4 \, \text{g}} \times 100 = 10\% \)

### Final Answer:
The percentage of nitrogen in the compound is **10%**.

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