Question

Given below are two statements:
Statement (I): Potassium sulphate, a constituent of digestion mixture, used in the digestion of milk sample in Kjeldahl method of protein estimation reduces the temperature of the contents.
Statement (II): Copper sulphate, a constituent of digestion mixture, used in the digestion of milk sample in Kjeldahl method of protein estimation, serves as catalyst.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true
• B. Both Statement (I) and Statement (II) are false
• C. Statement (I) is true but Statement (II) is false
• D. Statement (I) is false but Statement (II) is true

Hint:

In the Kjeldahl digestion mixture:
- Potassium sulfate (\(\text{K}_2\text{SO}_4\)) \(\rightarrow\) Raises the boiling point of the acid (increases temperature).
- Copper sulfate (\(\text{CuSO}_4\)) \(\rightarrow\) Speeds up the reaction (acts as a catalyst).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Kjeldahl method is the standard reference method used to estimate the nitrogen and crude protein content in milk and other food products.
The first and most critical step of this method is digestion, where the organic nitrogen in the milk sample is converted into ammonium sulfate (\((\text{NH}_4)_2\text{SO}_4\)) using concentrated sulfuric acid (\(\text{H}_2\text{SO}_4\)) under heat.

Step 2: Detailed Explanation:
Let us analyze the role of the reagents added to the digestion flask:
-Statement (I): "Potassium sulphate... reduces the temperature of the contents."
This statement is incorrect.
Concentrated sulfuric acid has a boiling point of approximately 337°C.
To completely digest complex proteins like casein, higher temperatures are required.
Potassium sulfate (\(\text{K}_2\text{SO}_4\)) is added to the digestion mixture to raise the boiling point of the acid, allowing the reaction to proceed at temperatures up to 370°C to 400°C.
This higher temperature accelerates the organic decomposition process, rather than reducing the temperature.
-Statement (II): "Copper sulphate... serves as catalyst."
This statement is true.
Anhydrous copper sulfate (\(\text{CuSO}_4\)) is added to the digestion mixture as a catalyst.
It speeds up the oxidation of organic matter and the conversion of organic nitrogen to ammonia.
Other metals like selenium or mercury can also be used, but copper sulfate is preferred because it is safer and less toxic.
Therefore, Statement (I) is false and Statement (II) is true.

Step 3: Final Answer:
Statement (I) is false but Statement (II) is true, which corresponds to Option (D).