Urea is heated in a test tube. A condensation reaction occurs.
Which one?
What is the formula for this reaction?
Then cupper sulphate and sodium hydroxide is added to the tube. This is compared to a tube in which cupper sulphate, sodium hydroxide and a solution of egg white are mixed.
What color does it turn into?
Which part of the protein molecule gives the characteristic color with cupper ions in a basic solution?
The reaction, depending on the conditions, is:
(H2N)2CO ---> NH3 + HNCO
The test you describe sounds like the biuret test for the peptide link. Both, urea and proteins have peptide links and give a positive test. If you have done this experiment, you should know the characteristic color.
Biuret is one of the thermal decomposition products of urea. Also, an impurity in urea. How pure was the urea used?
I highly recommend you study the materials related to this experiment. We can't "second guess" from afar what happened where you are.
To determine the condensation reaction that occurs when urea is heated in a test tube, we need to understand the composition and behavior of urea. Urea is an organic compound with the chemical formula (NH₂)₂CO. When heated, urea decomposes into two molecules of ammonia (NH₃) and carbon dioxide (CO₂) through a reaction called thermal decomposition.
The formula for the thermal decomposition of urea can be represented as:
(NH₂)₂CO → 2NH₃ + CO₂
Moving on to the second part of the question, when copper sulfate (CuSO₄) and sodium hydroxide (NaOH) are added to the test tube, a reaction occurs known as a precipitation reaction. This reaction results in the formation of a solid, which is typically a precipitate.
The chemical equation for the reaction between copper sulfate and sodium hydroxide is:
CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄
The resulting precipitate is copper(II) hydroxide (Cu(OH)₂), which appears as a blue solid.
Comparing this reaction to the tube where copper sulfate, sodium hydroxide, and a solution of egg white are mixed, we can observe a different color change. Egg white contains proteins, and one of the characteristics of proteins is their ability to bind with copper ions (Cu²⁺) in basic solutions.
Copper ions form coordination complexes with the protein molecules, resulting in a color change. In basic solutions, copper ions react with the protein structure and give a characteristic blue or purple color.
Therefore, the color observed when copper sulfate, sodium hydroxide, and a solution of egg white are mixed is typically a blue or purple color due to the interaction between the protein molecules and copper ions in a basic solution.