Analysis: Lab by- Gurpreet, Pratik and Rajat

1. Identify the control sample in each test you conducted. Explain how you know it is the control and why it is included.
For all of the tests, Distilled Water was the controlled sample because for the entire test the distilled water did not react with any of the solutes present inside the test tubes. It is included as a test sample because its composition contains no macromolecules.
Biuret Test for Protein- Distilled water, Starch, Glucose, Apple juice
These are the samples in which the color change didn’t occur and it contained no proteins.
Iodine Test for Starch- Distilled water, Albumin, Glucose, milk, whip cream, apple juice, gelatin
These are the samples in which the color change didn’t occur and it doesn’t have any starch in it.
Test of Reducing Sugar (Benedict’s)- Distilled water, Albumin, starch, gelatin
These are the samples in which the color change didn’t occur and it does not contain sugar.
Test for Lipids- Distilled water, starch, apple juice, gelatin, glucose
These are the samples in which are not translucent (clear) therefore; it doesn’t leaves oily spot on the brown paper.

2. Make a summary chart with the different 8 solutions that you tested. Identify which macromolecules are found in each of the solutions.

Solutions Macromolecules Found
Distilled water
None
Albumin solution
Proteins, lipids
Starch suspension
Starch
Glucose suspension
Carbohydrates
Milk
Protein, Carbohydrates, lipids
Whipping Cream
Protein, Carbohydrates, lipids
Apple juice
Carbohydrates
Gelatin Solution
Protein (few), Carbohydrates

3. Describe a positive test for

a) Protein- To test the protein, you need to add 2cm of Biuret solution to 1 cm of your sample. If it turns blue then it’s a negative test. So a positive test would be if it changes color to purple. The reagent used in the Biuret Test is a solution of copper sulfate (CuSO4) and potassium hydroxide (KOH), when the copper (II) ions are coordinated with the nitrogen atoms which are one of the contents of proteins, these peptide bonds the color of the solution changes from blue to violet. When the peptides are very short, the solution turns a pink color which means few proteins.

b) Starch- To test the starch you need to add 5 drops of iodine to your sample. If it turns blue it’s a negative test. Dark-blue, purple or even brown, it’s positive for starch. Amylose molecules are made up of single strands of glucose molecules. When iodine is added to a starch, it sticks to the beta amylose molecules because of their solubility. The starch pushes the iodine into a line in the middle of the amylose coils and creates a transfer of charge between the iodine and starch. This causes a change in the arrangement of electrons and energy level spacing’s. The new spacing’s absorb visible light differently and create the deep blue color. Thus changes its color in dark- blue when the iodine solution is added.

c) Sugars- To test the sugars you need to add 2cm of benedict’s solution to 1cm of your sample. After pouring the liquids, you need to add the