Have you ever wondered why some recipes call for baking soda, others for baking powder, and some for both? I've had several friends and coworkers, even, ask me the difference. At first glance they seem so similar. They are similar in appearance and can easily be confused for one another but even their containers are both orange. They were trying to trick us by doing that, I'm certain of it. However, there is a difference between the two so let's get down to the nitty gritty science of it all.
Baking soda and baking powder are both leaveners, therefore in baking they are used to make things rise. They react with other ingredients to create a gas that literally lifts our baked goods.
Baking soda, chemically known as sodium bicarbonate, has to be mixed with an acid to work. So you'll often see baking soda in a recipe that calls for lemons, chocolate, or buttermilk. The acid in those ingredients activate the baking soda causing the gas to do it's thing.
Baking powder, on the other hand, doesn't need an acid to work because the acid is already mixed in. Baking powder is actually a mixture of sodium bicarbonate and an acid, usually baking soda and cream of tartar. Heat is all that's required to activate baking powder. Because heat is the activating cue, it is okay to mix up doughs and batters ahead of time that have baking powder in them, whereas doughs and batters that have baking soda should be used right away. Once the acid and soda are mixed together, it starts working and if you let your batter sit for too long the baking soda will weaken, having already absorbed all of the acidity in the batter.
So, why do some call for both? Some recipes, like in our blueberry buttermilk pancakes, you want a nice tanginess. If you were to only use baking soda it would use up all of the buttermilk's acidity and you would lose that flavor in the finished product. If you add baking powder in addition to the baking soda you get to keep some of the acid and therefore your tanginess. Baking soda also adds color to baked goods which is why you don't only want to use baking powder. Taking the baking soda out of a recipe that calls for it will result in a depressing and pale colored treat that no one wants to eat. Using both in a recipe is also nice for smaller batches because too much baking soda in a recipe can make it taste like soap, using both will keep that from happening while also giving you the height you desire.
Now, go forth and bake fearlessly!