The iodine test is used to test for the presence of starch. Starch turns into an intense "blue-black" colour upon addition of aqueous solutions of the triiodide anion, due to the formation of an intermolecular charge-transfer complex. In the absence of starch, the brown colour of the aqueous solution remains.

Iodine solution is used to test the presence of starch in a food item by observing colour change.^_^

Testing for Starch using Iodine Solution

Starch is a type of carbohydrate that is commonly found in plants. Iodine solution can be used to test for the presence of starch in a substance. Here's how it works:

Principle: The iodine solution reacts with the starch to form a blue-black complex.

Procedure:

1. Take a small amount of the substance to be tested (e.g. potato, bread, rice, etc.) and place it on a white tile or plate.
2. Add a few drops of iodine solution to the substance.
3. Observe the color change:

- If the substance contains starch, it will turn blue-black.
- If the substance does not contain starch, there will be no color change.

Explanation:

Starch is a polysaccharide made up of glucose molecules. When iodine solution is added to a substance that contains starch, the iodine molecules slip inside the coils of the starch molecules and form a complex. This complex absorbs light differently than starch alone, causing the color change from brownish-yellow to blue-black.

Conclusion:

Iodine solution is a quick and easy way to test for the presence of starch in a substance. This test is commonly used in biology and chemistry labs to identify the presence of carbohydrates in food samples, plant tissues, and other materials.