Tag: Biology experiment

Biuret solution detects the presence of proteins by reacting with the peptide bonds that link amino acids together. When copper(II) ions in the reagent form a complex with these bonds in an alkaline environment, a color change from blue to violet or purple occurs, indicating a positive result.

A positive iodine test for starch produces a striking blue-black color, a reaction so sensitive it can be visually detected with very low concentrations of iodine. This simple chemical procedure is the standard method for confirming the presence of starch in various samples, from laboratory solutions to food products.

When a solution of iodine is dropped onto a cut potato, the initial yellowish-brown color of the iodine rapidly transforms into a deep blue-black or purple hue. This dramatic color change serves as a definitive indicator for the presence of starch, a complex carbohydrate abundant in potatoes and other plants.

According to scientific principles, iodine reacts with starch to produce a distinctive blue-black color. Therefore, to know if starch is not present in a sample, you must conduct the iodine test and observe for a negative result, where the yellow-brown color of the iodine solution remains unchanged.