Question

The carbohydrate sucrose dissociates (= separates) spontaneously into two smaller molecules,glucose and fructose. But if you add sucrose to water and wait a day, you still cannot detect glucose and fructose. Why not?

Answer 1

Sucrose, a disaccharide, remains intact in water because the covalent bonds between its glucose and fructose molecules are not broken by simply dissolving in water. To separate into monosaccharides, an enzymatic reaction is required which does not occur by just leaving it in water for a day.

Step-by-step explanation:

The student's observation that sucrose does not seem to separate into glucose and fructose when added to water and left for a day is due to the nature of how sucrose behaves in solution. Sucrose is a disaccharide composed of glucose and fructose molecules bonded together via a glyosidic linkage. When sucrose is dissolved in water, the solution consists of individual sugar molecules that are separated from each another by disruption of intermolecular attractive forces, but the covalent bonds that hold the glucose and fructose together within the sucrose molecule are not broken. The process of disassociating the disaccharide into monosaccharides, like glucose and fructose, requires an enzymatic reaction, specifically involving the enzyme sucrose. Absent this enzyme, sucrose remains intact in an aqueous solution. Therefore, after a day in water, without the enzyme, glucose and fructose are not present as separate entities, and thus can't be detected.