British Sign Language Glossaries of Curriculum Terms

BSL Chemistry Glossary - iodine solution - Definition

Iodine (I₂) solution is used to detect the presence of Starch.

When you drop it into a liquid you can see whether it has Starch in it. If it does, the starch doesn't easily dissolve in water because it's a long polymer.

In this test tube I have Glucose, in the other is Starch. Glucose is a single molecule, whereas Starch is much, much longer.

Watch out for the change in colour. Notice the colour stays the same - it's still brown which means there is no Starch present.

Have a look at the other one. Can you see the colour has changed to dark blue/black, that's because this test tube has Starch in it.

There are two ways of identifying the presence of Starch: the first is that it doesn't easily dissolve in water and the second is that it turns the colour of I₂ Solution from brown to blue/black.