Chapter 2

In the Middle Ages, alchemists labored to turn common materials such as iron into precious metals such as gold. If you could journey back in time, how could you convince an alchemist that iron cannot be changed into gold?

Why does a balloon filled with helium float? Hydrogen can make balloons float, but it is not used for this purpose today because it is flammable. Based on chemical principles reviewed in the chapter, can you see why helium is not flammable? ( Hint: Think what you are adding to a fire when you blow on it.)