When you pour iodine on baby powder, it tuns yellow. Let it sit for a while or add water, it turns...black.
We did that in my science class. Not sure whether or not to call it chemistry because the material is 3 grades above our current and we're all passing with flying colors.
![Laughing :lol:](./images/smilies/icon_lol.gif)
It also works with baking powder, baking soda, and flour.