Chemical Testing for Carbohydrates, Proteins, and Lipids in Lab

1. Chemical Aspects of LifeLab 4 Pre-lab Discussion

2. Background • In this lab you will be testing for the presence of the following substances: • Carbohydrates • Proteins • Lipids • You will use various chemical indicators to test for the presence of these substances. • Carbohydrates will be tested with Benedict’s solution and Iodine solution • Proteins will be tested with Biuret’s solution • Lipids will be tested with Sudan IV • Use the following chart as a reference:

3. The “Carb” Test with Benedict’s • The carbohydrate test is the most confusing. You really need to understand the difference between monosaccharides and disaccharides • Monosaccharides include: • Glucose • Fructose • Galactose • Disaccharides include: • Maltose – glucose + glucose • Lactose – glucose + galactose • Sucrose – glucose + fructose ***Remember: Disaccharides are formed by a condensation reaction. Once a chemical reaction has occurred you have an entirely new product. The reactants are gone.

4. The Benedict’s Test • Benedicts Solution is a blue indicator solution that reacts with monosaccharides. It will turn one of three colors depending on the concentration of monosaccharides in solution. • Red-brown—high concentration of monosaccharides • Orange—moderate concentration of monosaccharides • Green—low concentration of monosaccharides. • Blue—no monosaccharides

5. Carbohydrate Hypotheses • You will be testing 5% Glucose solution and 5% Sucrose solution with Benedict’s Solution. Write a hypothesis for each of these tests. • If Benedict’s is added to 5% Glucose solution then…. • If Benedict’s is added to 5% Sucrose solution then… • Hydrochloric acid can be added in place of water to produce a hydrolysis reaction. During this reaction, a disaccharide can be broken down into two monosaccharides. You will be testing 5% Sucrose + HCl with Benedict’s Solution. Write a hypothesis for this test. • If Benedict’s is added to Sucrose +HCl then…

6. Starch is a very large polysaccharide made when hundreds of glucose molecules join together through numerous condensation reactions. • You will be testing Starch and Benedict’s solution. You will also be testing Starch + HCl and Benedict’s solution. • Write a hypothesis for each of these tests. • If Benedict’s is added to a Starch solution then… • If Benedict’s is added to a Starch + HCl solution then…

7. The “Carb” test with Iodine • Iodine can be used to test for polysaccharides…particularly Starch • Iodine turns blue black in the presence of starch. • You will test starch and water with iodine. • Important test – will be used many times this year. Write Hypotheses statements for each of these tests. • If iodine is added to a starch solution, then… • If iodine is added to water, then….

8. Protein Tests • Biuret solution is a blue solution that turns a violet color in the presence of proteins • You will be testing egg albumin and gelatin with Biurets solution. Write hypotheses statements for each of these tests. • If Biuret solution is added to egg albumin, then … • If Biuret solution is added to gelatin, then….

9. Lipid Test: Grease Spot • Lipids in solution will leave a transparent spot on a brown paper bag. • You will test oil, water and milk by placing drops of each on a brown paper bag. Write hypotheses statements for each test. • If a drop of oil is placed on a piece of brown paper bag, then… • If a drop of water is placed on a piece of brown paper bag, then… • If a drop of milk is placed on a piece of brown paper bag, then…

10. Lipid Test: Sudan IV • Sudan IV is a red dye that is soluble in lipids, but not soluble in water. (Soluble means that it will dissolve in solution. Insoluble will float or sink). • You will be adding Sudan IV to a mixture of water and oil and then to a mixture of water and milk. Write hypotheses statements to predict where you will see the red color in the test tubes. • If Sudan IV is dropped into a water and oil mixture, then the dye will … • If Sudan IV is dropped into a water and milk mixture, then the dye will…