Question

During the Biuret's test, if a purple ring forms at the surface of the solution and the rest remains blue, what error occurred?

A) Incorrect pH level
B) Insufficient mixing
C) Wrong reagents used
D) Excessive heating

Answer 1

Insufficient mixing leads to a purple ring at the surface and blue color in the rest of the solution during the Biuret's test, which is used to detect peptides and proteins. The correct option is B.

Step-by-step explanation:

During the Biuret's test, if a purple ring forms at the surface of the solution while the rest remains blue, this indicates insufficient mixing of the reagents and sample. A Biuret test is used to detect the presence of peptides and proteins through complexation with copper ions in alkaline solutions.

When proteins or peptides are present, the color changes from blue to purple. However, if proper mixing is not achieved, the reagents may not have been evenly distributed throughout the solution, resulting in a purple ring at the surface where the copper sulfate from Biuret reagent meets the protein, and a blue color in the rest of the solution where the reagents have not interacted sufficiently with the sample.