powdered baking soda is just baking soda...but powderd into finer composition. i Baking soda is sodium bicarbonate, an alkaline (a base the opposite of an acid), which produces carbon dioxide when mixed with a liquid acid. but if u r asking about baking powder,..... then it is a mixture of baking soda, starch, and at least one slightly acidic compound such as cream of tartar that works as a leavening agent in baking by releasing carbon dioxide when mixed with a liquid, such as milk or water.