Quantitative Analysis

The question asks whether the Kjeldahl method is applicable for estimating nitrogen in pyridine and whether the nitrogen in pyridine can be easily converted to ammonium sulphate via this method.

1. Kjeldahl Method: This method is commonly used for determining the nitrogen content in chemical substances, primarily those organic compounds containing nitrogen in the form of ammonia or amines. The process involves digestion, neutralization, and titration to convert nitrogen into ammonium sulfate which is then measured.
2. Pyridine: Pyridine is a heterocyclic aromatic organic compound with the chemical formula . It has nitrogen in the form of a pyridine ring, which is not amenable to ready conversion into ammonia under the usual conditions of the Kjeldahl method.
3. Statement Evaluation:
   • Statement I: "Kjeldahl method is applicable to estimate nitrogen in pyridine."

This is false. The nitrogen in pyridine is part of a stable aromatic ring, which does not get converted into ammonia easily in the Kjeldahl digestion process. Hence, the Kjeldahl method is not appropriate for determining nitrogen in pyridine.

• Statement II: "The nitrogen present in pyridine can easily be converted into ammonium sulphate in Kjeldahl method."

This is also false. As mentioned earlier, the nitrogen in pyridine is not readily convertible to ammonium sulphate because of its stable aromatic nature.

Conclusion: Both Statement I and Statement II are false. The correct answer is: Both Statement I and Statement II is false.

To solve the question, we need to correctly match each test from List-I with the corresponding reaction sequence from List-II.

1. Borax Bead Test:
   This test is used to identify certain metals. The equation involved is:This sequence involves the use of Na₂B₄O₇ in the reaction. Hence, (A) Borax bead test matches with III.
2. Charcoal Cavity Test:
   This test helps to identify metal salts that, when reduced, leave a characteristic residue in the cavity. The equation is:This involves reactions happening on charcoal and hence, (B) Charcoal cavity test matches with IV.
3. Cobalt Nitrate Test:
   This is a test for the detection of compounds that produce cobalt or its oxides. The relevant equation is:The sequence involves cobalt nitrate, so (C) Cobalt nitrate test matches with I.
4. Flame Test:
   This test is used to detect the presence of certain metal ions, based on the color of the flame. The reaction is:It involves the burning of the sample, so (D) Flame test matches with II.

Thus, the correct matches are: A-III, B-IV, C-I, D-II.

The question asks to identify the specific role of copper sulfate (CuSO₄) in the Kjeldahl method, which is a technique used for the quantitative estimation of nitrogen in organic compounds.

Concept Used:

The Kjeldahl method involves three main steps:

1. Digestion: The organic compound containing nitrogen is heated with concentrated sulfuric acid ( ). The nitrogen in the compound is quantitatively converted into ammonium sulfate ( ). This step is often slow and is carried out at high temperatures.
2. Distillation: The resulting acidic solution is treated with an excess of a strong base (like NaOH) to liberate ammonia gas ( ). The ammonia is then distilled and absorbed in a known excess volume of a standard acid (e.g., or HCl).
3. Titration: The amount of unreacted acid is determined by titrating it against a standard base. This allows for the calculation of the amount of ammonia produced, and subsequently, the percentage of nitrogen in the original sample.

To facilitate the digestion process, certain substances are added to the digestion flask along with the sample and concentrated .

Step-by-Step Solution:

Step 1: Analyze the digestion step of the Kjeldahl method.

The digestion reaction involves the oxidation of the organic compound by hot, concentrated sulfuric acid. The reaction can be represented generally as:

This digestion process is typically very slow.

Step 2: Consider the role of additives in the digestion process.

To speed up the decomposition and digestion of the organic sample, two types of substances are commonly added:

• A salt to elevate the boiling point: Potassium sulfate ( ) is added to raise the boiling point of the sulfuric acid (from ~337 °C to ~370-400 °C). This allows the digestion to proceed at a higher temperature, which significantly increases the reaction rate.
• A catalyst: A metallic salt is added to catalyze the oxidation of the organic matter. This further accelerates the rate of digestion.

Step 3: Identify the specific function of CuSO₄.

Copper(II) sulfate ( ) is one of the most commonly used catalysts in the Kjeldahl method. Its function is to increase the rate of the reaction between the sulfuric acid and the organic compound. It does so by facilitating the oxidation process, allowing the conversion of organic nitrogen to ammonium sulfate to occur more quickly and efficiently. Other catalysts like selenium or mercury(II) oxide can also be used, but CuSO₄ is a popular choice.

Final Result:

In the digestion step of Kjeldahl’s method for nitrogen estimation, copper sulfate (CuSO₄) acts as a catalyst to increase the speed of the reaction.