Question

QUESTIONS: 1. When a reducing sugar reacts with Benedict reagent, what organic product is formed besides Cu20? Why is the formation of Cu O significant in this test? 2. What chemical test is performed to indicate the completion of the hydrolysis of starch by acid?

Answer 1

Qn:1 Benedict's reagent #It is a chemical reagent and complex mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate. #It is used to detect the presence of reducing sugars #The positive test with Benedict's reagent is observed by a color change from clear blue to brick-red with a precipitate. #This test detects the presence of aldehydes, alpha-hydroxy-ketones, and hemiacetals, including those that occur in certain ketoses. Bendicts reagent converts aldehydic part of reducing sugar indo carboxylate ion This is the organic product formed during the reaction. + RH Cu2+ + 5 OH + Cu2O + 3H20 - R carboxylate ion The formation of Cu O is important in the benedicts test. Because Cu?is reduced into Cu". This is the indication of bendects tests happened or not. Qn:2 #The test for the completion of hydrolysis of starch is Starch-iodine test. #In this test sample turns blue-black in color when a few drops of potassium iodide solution is placed on the sample. #The reaction is happened due to the formation of polyiodide chains from the reaction of starch and iodine. #The amylose in starch forms helices where iodine molecules assemble, forming a dark blue or black color. #When starch is broken down or hydrolyzed into smaller carbohydrate units, the blue-black color is not produced. # Hence, this test can also indicate completion of hydrolysis when a color change does not occur. #This is also called as Iodine test.