What is ________ used for?

I have decided to occasionally write what, or why certain ingredients are used for recipes and others are not. I always wonder and am probably not the only one, what is the difference baking powder and baking soda?

in a nutshell it's their chemistry (ugh i though i would be done with this for a long while!). baking soda is pure sodium bicarbonate, which means that when put with an acidic product it creates carbon dioxide so when you stuff your food in the oven the reaction causes things to rise. (this is why you use it with dairy products, chocolate, honey...)

baking powder has sodium bicarbonate as well as the acid and a drying substance, like a starch. what determines which one you use? (this, from chemistry.com)
Baking soda is basic and will yield a bitter taste unless countered by the acidity of another ingredient, such as buttermilk. You'll find baking soda in cookie recipes. Baking powder contains both an acid and a base and has an overall neutral effect in terms of taste. Recipes that call for baking powder often call for other neutral-tasting ingredients, such as milk. Baking powder is a common ingredient in cakes and biscuits.

You can substitute baking powder in place of baking soda (you'll need more baking powder and it may affect the taste), but you can't use baking soda when a recipe calls for baking powder. Baking soda by itself lacks the acidity to make a cake rise. However, you can make your own baking powder if you have baking soda and cream of tartar. Simply mix two parts cream of tartar with one part baking soda.

now, you know!