AP BIOLOGY

Detailed explanation-1: -Using an iodine solution, you can test for the presence of starch. When starch is present, the iodine changes from brown to blue-black or purple.

Detailed explanation-2: -Iodine-KI Reagent: Iodine does not completely soluble in liquids, so the iodine reagent is formulated in the presence of potassium iodide by breaking down iodine in liquids. This creates the complex of a linear triiodide ion soluble, which slides into the starch coil, creating a vivid blue-black appearance.

Detailed explanation-3: -Amylose present in starch is the reason for change in its colour to blue black. Iodine is not soluble in water so it is dissolved along with potassium iodide that forms a triiodide molecule which enters the helical structure of amylose and changes the colour of starch.

Detailed explanation-4: -Iodine Test Using iodine to test for the presence of starch is a common experiment. A solution of iodine (I2) and potassium iodide (KI) in water has a light orange-brown color. If it is added to a sample that contains starch, such as the bread pictured above, the color changes to a deep blue.