Baking soda is pure bicarbonate of soda also known as sodium bicarbonate. It is an alkaline ingredient, and when mixed with acidic ingredients, it reacts and releases bubbles of carbon dioxide. Baking soda is single acting, it only reacts once it is combined with moisture. It has baking and household uses.
Baking powder is used for baking. It is made up of sodium bicarbonate (baking soda); an acid salt which reacts with moisture or heat, or both – such as tartaric acid, mono-calcium or combination of acid salts; and cornstarch (used to keep ingredients separated). Baking powder is double acting, it reacts once when mixed with moisture and again when it is exposed to high temperatures.