If you place starch or maltose in Benedict's solution, would a brick red precipitate be formed? Why or why not

Answer 1

Benedict's reagent (also called Benedict's solution or Benedict's test) is a reagent consisting of hydrated copper sulfate used as a test for the presence of monosaccharides (such as glucose and fructose); it is also used for some disaccharides like maltose, or more generally for the presence of aldehydes, in a solution.

Benedict's reagent contains blue copper sulfate (CuSO4)· 5H2O which is reduced to red copper oxide by aldehydes, thus oxidizing the aldehydes to carboxylic acids. The copper oxide is insoluble in water and so precipitates. The color of the final solution ranges from green to brick red depending on how many of the copper ions are present. Benedict's test cannot be used to detect the presence of aromatic aldehydes.

Answer 2

Yes for maltose and no for starch.

Maltose is a disaccharide of two glucose units linked by alpha 1- glycosidic bonds. One reducing end (at C1) is not involved in bond linkage and is available to reduce copper (II) to brick red copper (I) in the solution. There is one reducing end for every one small maltose molecule.

Starch is a polysaccharide with glucose linked with 1-4 and 1-6 bonds. There are available reducing ends at some terminal glucose subunits where the C1 is not involved in bond linkage. However, due to the large number of subunits (up to thousands) of glucose in starch compared to the few number of reducing ends it have, the reducing effect of starch is very very minimal and would not cause color change in Benedict's solution