Baking soda contains one ingredient, sodium bicarbonate. However, Baking powder contains sodium bicarbonate, monocalcium phosphate and either sodium acid pyrophosphate or sodium aluminum sulfate.
Baking soda contains one ingredient, while baking powder has a few. Baking soda also requires an acid and a liquid to become activated (or in baking, it needs an acid and liquid to help rise) and for baking powder, it only needs a liquid to become activated (or help rise).
