Estimation of nitrogen: There are two methods for the estimation of nitrogen (i) Dumas method and (ii) Kjedahl's method.
i. Dumas method: A known mass of compound is heated with copper oxide (CuO) in an atomsphere of `CO_(2)`, which gives free nitrogen along with `CO_(2) and H_(2)O`
`C_(x)H_(y)N_(z) + (2x + y//2) CuO rarr xCO_(2) + y//2 (H_(2)O) + z//2 (N_(2)) + (2x + y//2) CU`
The gaseous mixture is passed over a heated copper gauze which converts traces of nitrogen oxides formed to `N_(2)`. The gaeous mixture is collected over an aqueous solution of KOH which absorbs `CO_(2)`, and nitrogen is callected in the upper part of the graduated tube.
ii. Kjeldahl's method: A known mass of organic compound (0.5 gm) is mixed with `K_(2)SO_(4)` (10 gm) and `CuSO_(4)`. (1.0 gm) or a drop of mercury (Hg) and conc. `H_(2)SO_(4)` (25ml), and heated in Kjeldahl's flask. `CuSO_(4)` or Hg acts as a catalyst, while `K_(2)SO_(4)` raises the boiling point of `H_(2)SO_(4)`. The nitrogen in the organic compound is quantitatively converted to ammonium sulphate. The resulting mixture is then distilled with excess of NaOH solution and the `NH_(3)` evolved is passed into a known but excess volume of standard HCl or `H_(2)SO_(4)`. The acid left unused is estimated by titration with some standard alkali. The amount of acid used against `NH_(3)` can be thus be known and from this the percentage of nitrogen is calculated.
(a) `C + H + S underset(H_(2)SO_(4))overset("conc.")rarr CO_(2) + H_(2)O + SO_(2)`
(b) `N underset(H_(2)SO_(4))overset("conc.")rarr (NH_(4))_(2)SO_(4)`
(c) `(NH_(4))_(2) SO_(4) + 2NaOH rarr Na_(2)SO_(4) + 2NH_(3) + 2H_(2)O`
(d) `2NH_(3) + H_(2)SO_(4) rarr (NH_(4))_(2) SO_(4)`
(iii) This method is not applicable to compounds containing N in intro and azo groups, and N present in the ring (e.g., pyridine) as N of these compounds does not change to `(NH_(4))_(2)SO_(4)` (ammonium sulphate) under these reaction conditions
0.002 gm of an organic compound was treated according to Kjeldahl's method. `0.2 xx 10^(-4) mol` of `H_(2)SO_(4)` was required to neutralise `NH_(3)`. Calculate the percentage of `N_(2)`

Options

A. 50
B. 28
C. 70
D. 18

Answer

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

### Step 1: Calculate the moles of sulfuric acid (H₂SO₄)
Given that the moles of H₂SO₄ required to neutralize the ammonia is \(0.2 \times 10^{-4}\) mol.

### Step 2: Determine the basicity of sulfuric acid
The basicity of sulfuric acid (H₂SO₄) is 2 because it can donate two protons (H⁺ ions).

### Step 3: Calculate the equivalents of sulfuric acid
The equivalents of H₂SO₄ can be calculated using the formula:
\[ \text{Equivalents of H₂SO₄} = \text{Moles of H₂SO₄} \times \text{Basicity} \]
Substituting the values:
\[ \text{Equivalents of H₂SO₄} = (0.2 \times 10^{-4}) \times 2 = 0.4 \times 10^{-4} \text{ equivalents} \]

### Step 4: Convert equivalents to milliequivalents
To convert the equivalents to milliequivalents, we multiply by \(10^3\):
\[ \text{Milliequivalents of H₂SO₄} = 0.4 \times 10^{-4} \times 10^3 = 0.4 \times 10^{-1} = 0.04 \text{ milliequivalents} \]

### Step 5: Use the formula to calculate the percentage of nitrogen
The formula to calculate the percentage of nitrogen in the organic compound is:
\[ \text{Percentage of } N = \frac{1.4 \times \text{milliequivalents of H₂SO₄}}{\text{mass of organic compound}} \times 100 \]
Substituting the values:
\[ \text{Percentage of } N = \frac{1.4 \times 0.04}{0.002} \times 100 \]

### Step 6: Calculate the percentage
Calculating the value:
\[ \text{Percentage of } N = \frac{0.056}{0.002} \times 100 = 28\% \]

### Final Answer
Thus, the percentage of nitrogen in the organic compound is **28%**.

---