Copper Sulphate and Caustic Soda
Explanation
The Biuret test is a standard chemical test used to detect the presence of peptide bonds, which are the structural links holding amino acids together in proteins. The test relies on the formation of a coordination complex between copper ions and peptide bonds in an alkaline solution.
Detailed Analysis:
- Reagents Used: The test utilizes an alkaline solution of Copper Sulphate ($CuSO_4$) and Caustic Soda (Sodium Hydroxide, $NaOH$).
- Function of Reagents:
- Caustic Soda: Creates the necessary alkaline environment for the reaction to occur.
- Copper Sulphate: Provides the Copper(II) ions ($Cu^{2+}$).
- Observation: In the presence of proteins, the blue copper(II) ions coordinate with the nitrogen atoms of the peptide bonds to form a complex that turns the solution violet or purple.
- Incorrect Options: Iodine solution is typically used to test for the presence of starch (carbohydrates), turning blue-black, and is not involved in protein detection.
Key Takeaway:
The Biuret test detects proteins using a mixture of Copper Sulphate and Caustic Soda, resulting in a color change from blue to violet due to the reaction with peptide bonds.