So while discussing phase changes, one consistent misconception is about what’s inside the bubbles in boiling water. Often students believe it’s just air, or more specifically hydrogen and oxygen gas. I asked then what would happen if I held a match over boiling water. Would it explode? To show them a hydrogen explosion, I tossed some zinc in HCl and lit the escaping gas. Once again the powerful model they have been developing paired some new empirical data let them see the world more clearly.