Baking Soda or bicarbonate of soda is a leavening agent in baked goods like cookies or quick breads. It is used when the dough or batter contains an acidic ingredient, like buttermilk, lemon, brown sugar, sour cream or yogurt. The soda or base combines with the buttermilk or acid, to produce carbon dioxide and the baked goods expand, or rice. It is an ingredient in baking powder. Make sure not to confuse the two when baking or your product will be ruined.