Baking soda, baking powder, and yeast are used to make batters and dough rise.
Recipes that include such acidic ingredients as buttermilk, honey, cocoa powder, or molasses call for baking soda, which works with the acid to cause rising. It's often used to make cookies.
You can use baking powder whether or not the recipe contains acidic ingredients. The most commonly available baking powder is called double-acting, meaning it works in two stages: It's activated when exposed to moisture as the batter is being mixed, and again when exposed to heat. It's mostly used for cakes, cookies, pancakes, and muffins.
How to Store
Both baking soda and baking powder need to be stored away from humidity, in a very dry place. Before buying and using, make sure to check the expiration or use-by date.
Yeast is a leavener used mainly in bread baking. There are two types of dry yeast: active dry and rapid rise (or instant). Your recipe will tell you which kind to buy. Active dry yeast needs to dissolve in warm water (not hot) before being mixed with other ingredients; rapid rise can be stirred right in. Make sure active dry yeast works before using it. Here's how to test (or proof) it: dissolve yeast in warm water; let stand 5 minutes. If the water gets bubbly, the yeast is working; if not, discard and start with a new packet or jar. Yeast is usually found in the dairy section. Check the use-by date before purchasing, and store in a dry part of the refrigerator.