is the following positive in a biuret test?
skim milk
purified casein
purified lactose
dextrose
You should get a second opinion but I believe the answer is skim milk. However, I'm not an organic chemist.
To determine if a substance would give a positive result in a biuret test, you need to understand the principle behind the test and the compound it detects.
The biuret test is commonly used to detect the presence of proteins, specifically those containing peptide bonds. Peptide bonds are chemical bonds that link amino acids together to form proteins.
During the biuret test, a reagent, usually a solution of copper sulfate (CuSO4), is added to the test sample. In the presence of peptide bonds, the copper ions in the reagent form a purple complex known as the biuret complex.
Now, let's examine the substances in your question:
1. Skim milk: Skim milk contains various proteins, including casein. Therefore, it is expected to give a positive result in the biuret test.
2. Purified casein: Casein is a protein found in milk, particularly in the curd part. As it is a protein, purified casein would also give a positive result in the biuret test.
3. Purified lactose: Lactose is a sugar found in milk and is not a protein. Therefore, purified lactose would not give a positive result in the biuret test.
4. Dextrose: Dextrose, also known as glucose, is a simple sugar. It does not contain peptide bonds and is not a protein. Hence, dextrose would not give a positive result in the biuret test.
In summary, the substances skim milk and purified casein would give a positive result in the biuret test, while purified lactose and dextrose would not.