Question

Questions: 1. What is responsible for a positive Benedict's test? 12-KI test? 2. What is responsible for a positive Biuret test? How are lipids detected? 3. Which biomolecules are present in the food samples? Procedure: Benedict's test 1. Fill 100 mL Beaker with 40 mL of water. 2. Place the burner stand over the burner and light it up using a match. 3. Place the beaker containing water over the burner stand to make a water bath. 4. Label 3 test tubes with (A, B, C). 5. Carefully mix the food sample, blank, and control with the reagent in every test tube. 20 drops Benedict's reagent + 10 drops food sample 1 b. a. 20 drops Benedict's reagent + 10 drops blank (water) c. 20 drops Benedict's reagent + 10 drops control (glucose) 6. Place the test tubes in the water bath for 5 minutes 7. Remove the tubes from water bath and record your observation Biuret Test 8. On a ceramic plate mix the food sample, blank, and control with the reagent on 3 spots a. 3 Drops Biuret reagent + 3 drops food sample 2 b. 3 Drops Biuret reagent + 3 drops blank (water) C. 3 Drops Biuret reagent +3 drops control (Egg white) 9. record your observation. 12-KI Test 10. Label 3 test tubes with (A, B, C). 11. Carefully mix the food sample, blank, and control with the reagent in every test tube. a. 3 drops I-KI reagent + 3 drops food sample 3 b. 3 drops I,-KI reagent + 3 drops blank (water) c. 3 drops 12-KI reagent + 3 drops control (Starch) 12. Record your observation Filter paper test 13. Smear or apply a drop of food sample, blank, and control over three separate clean spots on a piece of filter paper Exercise 1: Test for Biomolecules Observations Test Reagent Test Sample 1 Benedict's a. Food sample 1 reagent b. Blank: Water c. Control: Glucose 2 Biuret a. Food sample 2 reagent b. Blank: Water c. Control: Egg white a. Food sample 3 b. Blank: Water c. Control: Starch a. Food sample 4 b. Blank: Water c. Control: Oil 3 12-Kl reagent 4 Filter paper

Answer 1

Q.1 Benedict test help us to identify the presence of free aldehydic or ketonic group in the sample. This test is especially used for reducing sugars. Positive Benedict test results in the formation of reddish precipitate giving the conformation of presence of reducing sugar. Iodine does not react with reducing sugars and so when iodine (which is red) is added to such a solution, no color change will be observed and if starch is present, a blue/black color change explains the presence of starch.

Q.2 Biuret Test determines the presence of peptide bonds. It relies on the reaction between copper ions and peptide bongs of the protein and color change from blue to violet indicates the presence of protein.

Lipids are detected or identified by Emulsion test where lipids are suspended in ethanol until they dissolve after that the sample liquid is decanted into the water . As lipids are insoluble in water, a cloudy white emulsion is formed when the ethanol is diluted.

Q.3 The biomolecules is the term used for the molecules or ions present in the organism. The four types of biomolecules present in the system is Nucleic acids, lipids, protein and Carbohydrates.