What happens inside biscuits and cookies as they bake? They go into the oven as thick dough. Then baking soda or baking powder makes them inflate: tiny pockets of air form inside the dough, making it rise. This experiment exposes the mystery of the rising dough.
What You’ll Need
1 teaspoon baking soda
1 teaspoon baking powder
4 small cups or containers
2 tablespoons vinegar
What to Do
Place the baking soda into one cup and the baking powder into a separate cup.
Place 1 tablespoon of vinegar into each of the other two cups.
Pour the vinegar over the powders at the same time.
Watch what happens.
How It Works
Both mixtures bubbled up, and the one with baking powder fizzed longer than the one with baking soda. Here’s why.
In both cups, reactions took place between two chemical families: bases and acids. The reactions released carbon dioxide gas, which made a lot of little bubbles, or fizz.
In one cup, baking soda (a base called sodium bicarbonate) reacted with acetic acid in the vinegar. The chemical reaction stopped once the acid was used up.
In the cup with baking powder, the same chemical reaction took place because baking powder contains baking soda. But baking powder also contains at least one more kind of acid. These acids come in dry forms that won’t react until they mix with water. So after the acetic acid in the vinegar was used up, the other acids were able to keep reacting with the baking soda because of the water in the vinegar.
Why do we have both baking soda and baking powder? A recipe must have the right balance between acids and bases. If all of the acids and bases are not used up, then the food will have too much of one or the other. Too much acid tastes sour. Too much base tastes bitter.
Some recipes have acidic ingredients, such as buttermilk or yogurt. They call for baking soda to use up the acids. Other recipes have almost no acids. They call for baking powder, which has the right balance to make the dough rise with no leftover acid or base.
