baking powder is used as a volumner and as a softner too. it is used  in cakes , pastries ,  puddings , and biscuites and in normal cooking foods . baking powder is basically just baking soda with some extra leavening and reacting agents in it for cooking, when it "expires" for your baking uses, you can still use it as baking soda (sodium bicarbonate). It can be used as a cleaning agent for scrubbing stains in sinks and on countertops.