The most universal use of baking soda (bicarbonate of soda) is for baking in which baking soda is used to promote leavening. Leavening increases the surface area of dough or batter by causing it to rise and become light and porous. The most common leavening agent is carbon dioxide, a gas that is produced by a chemical reaction with the use of baking soda, baking powder or yeast in a recipe. Baking soda yields the carbon dioxide for leavening when it's heated. When used as a leavening agent, baking soda also reacts with acidic ingredients to render a neutral, tasteless residue. Common examples of these acidic ingredients include sour milk, buttermilk, molasses, cream of tartar, lemon juice and the acidic substances in baking powder.