Baking soda and baking powder make baked goods rise. They release gases that give muffins, breads and cakes a lift as they bake.
Baking soda (sodium bicarbonate) requires a liquid and an acid in order to activate its leavening (rising) powers. The acid can be buttermilk, citrus juice, sour cream, honey or molasses. Once baking soda is mixed with a liquid and acid, it will start producing carbon dioxide gas so it should be baked immediately before the gas escapes from your batter or dough, leaving your baked goods flat.
Baking powder is typically made of sodium bicarbonate and other acids. Single-acting baking powder requires only moisture to activate it. Double-acting baking powder, the most common type, releases a little gas when it’s mixed with a liquid and more when it’s heated.
Some recipes call for both baking soda and baking powder when the leavening action from one isn’t enough.