Both baking powder and baking soda are chemical leavening agents that cause batters to rise when baked. The leavener enlarges the bubbles which are already present in the batter produced through creaming of ingredients. When a recipe contains baking powder and baking soda, the baking powder does most of the leavening. The baking soda is added to neutralize the acids in the recipe plus to add tenderness and some leavening
Baking soda, also known as sodium bicarbonate or bicarbonate of soda (alkali) is about four times as strong as baking powder. It is used in recipes that contain an acidic ingredient (e.g. vinegar, citrus juice, sour cream, yogurt, buttermilk, chocolate, cocoa (not Dutch-processed), honey, molasses (also brown sugar), fruits and maple syrup).
Baking soda starts to react and release carbon dioxide gas as soon as it is added to the batter and moistened. Make sure to bake the batter immediately.
Baking soda has an indefinite shelf life if stored in a sealed container in a cool dry place. Too much baking soda will result in a soapy taste with a coarse, open crumb. Baking soda causes reddening of cocoa powder
when baked, hence the name Devil's Food Cake