Benedict's reagent is a chemical that is used as a test for the presence of a free aldehyde functional group on glucose.The aldehyde is used when glucose and fructose bind together to form sucrose,and the Benedict's test is negative.Starch contains a great deal of glucose but gives a negative Benedict's test because:
A)all of the aldehyde groups on the starch are oxidized and cannot react with the Benedict's reagent.
B)starch is not soluble in water and cannot react with Benedict's reagent.
C)glucose in starch has lost a carbon atom and cannot react with Benedict's reagent.
D)only the glucose at the end of a chain of starch will have an exposed aldehyde functional group to react with Benedict's reagent.

Question

Quizplus · Accepted Answer

Starch is made up of glucose molecules that are linked together through glycosidic bonds. Only the glucose molecule at the end of the chain will have an exposed aldehyde functional group that can react with Benedict's reagent. The other glucose molecules in the chain will have their aldehyde groups involved in the glycosidic bond and will not react with Benedict's reagent. Therefore, even though starch contains a large amount of glucose, it will give a negative Benedict's test since only a small percentage of the glucose molecules will have a free aldehyde functional group.

Benedict's Reagent Is a Chemical That Is Used as a Test