Answer:
It is a test for proteins in urine
Explanation:
The Biuret reagent is made of sodium hydroxide (NaOH) and hydrated copper(II) sulfate. The biuret reagent is commonly used to test for proteins. The biuret test is also known as Piotrowski's test. It is a chemical test commonly used in detecting the presence of peptide bonds. In the presence of peptides, a copper(II) ion forms purple-colored coordination complexes in an alkaline solution.
Hence the addition of this Biuret reagent to a urine sample in a test tube aims to detect the presence or absence of proteins in the given urine sample. If there is protein in the urine sample, the blue colour of the Biuret reagent turns purple. If there is no protein in the urine sample, the Biuret reagent remains blue.
In an alkaline solution, copper II is able to form a complex with the peptide bonds in proteins. Once this complex has been formed, the Biuret solution turns from a blue color to a purple color. This is the positive test for proteins.
