Will iodine react with sucrose or glucose? I would say no, because it reacts with starch, a polysaccharide, and glucose is a monosaccaride and sucrose is a combination of fructose and glucose, two monosaccharides. Am I right? Why or why not? How does iodine cause a reaction to starch? Thanks!

When iodine iw dissolved in an aqueous solution of potassium iodide — it reacts with starch producing a purple black color.

Sra

Yes, you are correct. Iodine does not react directly with sucrose or glucose. Iodine primarily reacts with starch, a polysaccharide made up of repeating glucose units. The reaction occurs due to the presence of helical structures in starch called amylose and amylopectin.

Iodine forms a complex with these helical structures, resulting in a distinct color change from golden-brown to blue-black. This is commonly used as a test to detect the presence of starch in various substances. The iodine molecules fit into the helical structure of starch, forming a stable complex.

On the other hand, glucose is a monosaccharide, meaning it consists of a single sugar unit. Similarly, sucrose is a disaccharide made up of glucose and fructose. Since neither glucose nor sucrose have the same helical structure as starch, they do not form a complex with iodine. Consequently, there is no observable color change when iodine comes into contact with glucose or sucrose.

Yes, you are correct. Iodine does not react with sucrose or glucose. The reason for this lies in the chemical structure of these compounds.

Sucrose is a disaccharide, composed of one glucose molecule linked to one fructose molecule. Glucose and fructose are both monosaccharides, which are simple sugars. In sucrose, the bond between glucose and fructose is a glycosidic bond, and this prevents iodine from reacting with either of them.

On the other hand, iodine reacts with starch, a polysaccharide that is composed of hundreds to thousands of glucose molecules joined together. This reaction happens because iodine forms a complex with the linear or helical chains of glucose molecules in starch. This complex is characterized by a dark blue-purple color and is commonly used as a test for the presence of starch.

The iodine-starch reaction occurs due to the formation of an inclusion complex, where the iodine molecules fit within the helical structure of starch, causing the change in color. This reaction is an example of molecular recognition, where the specific shape and chemical properties of starch enable it to interact with iodine.

In summary, iodine does not react with sucrose or glucose because of the glycosidic bond present in sucrose and the chemical structure of glucose. Iodine causes a reaction with starch due to its specific interactions with the linear or helical structure of glucose molecules present in starch.