Baking Soda (Sodium bicarbonate) is used in cooking and baking as a raising agent. With baking it reacts to make a dioxide that helps dough rise. The acidic compounds that induce this reaction include tartric Acid, lemon juice, yoghurt, buttermilk, cocoa, vinegar, honey etc.
Baking soda can be substituted for baking powder provided sufficient acid reagent is also added to the recipe. Many forms of baking powder contain sodium bicarbonate combined with tartric acid.