Add about an inch of water to a large test tube followed by a couple drops of phenolphthalein pH indicator, which you will likely need to obtain from your classroom. Add a small pinch of washing soda, which contains sodium carbonate, Na₂CO₃. Upon mixing, the washing soda turns the solution basic, as evidenced by the pink color that forms. Neutralize this base by adding an acid, but not just any acid—use the acid of your breath. Bubble your breath into the solution through a straw until the pink color disappears. What acid are you adding? How does this activity relate to the acidity of rain? Why do you want to add only a small pinch of washing soda and not a tablespoon?