Chemistry and biology
MIT's choose-your-own: Chemistry adventure
WHITNEY: So this is hydrogen peroxide. You might recognize it from your first aid kit, because it's really good at killing germs. But there's more to this guy than cleaning cuts. So this liquid is actually made up of molecules that are constantly wanting to break apart. Hydrogen peroxide, or H2O2, is held together by an unstable bond-- this one, between the oxygen atoms. So the molecule wants to break down into smaller, more stable pieces-- H20, or water, and O2, or oxygen gas. Now this breakdown is usually so slow, we can't even see it happening. But what if we did want to see it happen? We can speed up this reaction a lot by using yeast. Yeast makes something called catalase, and what this does is speed up the breakdown of hydrogen peroxide, and something that speeds up a chemical reaction is called a catalyst. And the reason yeast makes catalase is because hydrogen peroxide damages cells and DNA. So the catalase goes around and breaks apart hydrogen peroxide, so it can't damage the yeast. And actually our bodies have catalase too, to protect our cells and DNA. And the cool thing is the catalase doesn't get used up at all in the process. So it keeps going around, breaking apart the hydrogen peroxide, quickly releasing oxygen gas and water. And normally this oxygen gas would just get released out into the air, but for fun, we can trap it in soap bubbles. This is the hydrogen peroxide you can buy at the drugstore. It's not very strong. It's only 3%. But this one is 30%. I'm diluting this down with water to 12%, mixing one milliliter of dish soap, and some food coloring. I'm also taking a gram of yeast and activating it with four milliliters of warm water. So what do you think will happen if we mix all these together? So pretty cool. But can we get even more foam? Can we make it faster? Let's tweak each of the ingredients one at a time and figure out how they affect the reaction. Should we change the amount of hydrogen peroxide, the amount of soap, or the amount of yeast?