Question

When you use iodine to test for starch, a color change to blue-black indicates a positive starch test.

True or False?

Answer 1

A color change to blue-black after adding iodine to a substance is a positive indication of the presence of starch, due to the formation of an amylose-iodine complex.

Step-by-step explanation:

The statement is true; using iodine to test for starch results in a color change to blue-black, which indicates a positive test for starch. This color change is due to the formation of a complex between iodine molecules and the spiral structure of amylose, one of the components of starch. Amylose is a linear polysaccharide made of D-glucose units linked together, which coils into a helix that can trap iodine molecules, resulting in the characteristic blue-black color.

Answer 2

The statement "When you use iodine to test for starch, a color change to blue-black indicates a positive starch test" is True.

Step-by-step explanation:

The use of iodine to test for starch is based on a chemical reaction where iodine interacts with the starch polymer amylose, producing a blue-black color.

Starch, which is a mixture of two polymers, amylose and amylopectin, reacts with iodine when the iodine molecules become lodged within the coiled structure of amylose, leading to the formation of a starch-iodine complex.

This reaction is highly sensitive and can detect even minute amounts of starch in a solution.

The visible dark blue to black color change upon the addition of iodine to a starch solution is indeed indicative of a positive test for starch.

Therefore, the statement that a color change to blue-black indicates a positive starch test when using iodine is True.