How does iodine work as an indicator?

Iodine detects starches. http://antoine.frostburg.edu/chem/senese/101/redox/faq/starch-as-redox-indicator.shtml

Why might starch not be able to diffuse but iodine can? I'm writing a lab report for a lab we did in Biology class, but I'm not sure what reason to put for why the starch could not diffuse through the bag we used in the experiment but the iodine could.

Iodine is commonly used as an indicator to test for the presence of starch in a substance. It is able to do so because of a chemical reaction between iodine and starch.

To understand how iodine works as an indicator for starch, let's discuss the chemical reaction that occurs. When iodine comes into contact with starch, a complex is formed between the iodine and the starch molecules. This complex has a blue-black color, which is easily distinguishable and indicates the presence of starch.

Now, let's see how this can be used practically. If you want to use iodine as an indicator to test for starch, you would typically perform the following steps:

1. Take a small sample of the substance you want to test, such as a piece of food or a plant material.

2. Add a few drops of iodine solution to the sample. Iodine solutions can be easily obtained in drugstores or prepared by dissolving iodine in water.

3. Observe the color change. If the sample contains starch, it will react with the iodine and turn blue-black. On the other hand, if there is no starch, there will be no color change.

It's important to note that iodine does not react with other carbohydrates or sugars, making it selective for detecting starch specifically.

In summary, iodine works as an indicator for starch by forming a blue-black complex with starch molecules. By adding iodine solution to a sample and observing a color change, you can determine whether or not the sample contains starch.