Acid is required when using chemical leavenings such as baking soda or baking powder. Visualize the baking soda and vinegar volcanoes of your elementary school science projects. Just like that, but on a much smaller scale, acid reacts with baking soda to release carbon dioxide bubbles to leaven baked goods. Doughs and batters leavened by baking soda should also have an acidic ingredient such as natural cocoa powder, brown sugar, honey, or buttermilk. Baking powder, on the other hand, already contains powdered tartaric acid and doesn’t need an external source of acid to react.