Listen up bake fans. Cooking is different from baking because of one essential reason. Cooking is an art form, baking is a science. What does that mean? Glad you (didn't) ask. That means when a baking recipe tells you to do something you do it without question! Think of it as martial law, especially when you're going though the recipe for the first time. Some of the culinary art's most spectacular fails have happening in baking. You can at least modify a cooking recipe and save it. Ever try to separate a tablespoon of salt from four cups of flour. Forget it kid, you're now officially screwed to the wall.
Hence my explanation of what baking soda and baking powder are and why they are SO not interchangeable. (That's an SAT word for - you can't substitute one for the other.) You can only use the powder in place of the soda, and even then you should know what you're doing first! They are both leavening agents, which mean they make baked goods rise, but they do this in different ways.
Baking Powder consists of:
- sodium bicarbonate
- sodium aluminum sulfate
- monocalcium phosphate
- The acidifying agents (sodium & phosphate) will cause carbon dioxide to be released and that gets the recipe in question going with the leavening action.
- The heat from the oven makes the gases expand, causing the rest of the dough, batter, ect to rise.
- sodium bicarbonate
Moving on. Baking soda used in cooking is to quick start the leavening process. It releases the carbon dioxide very quickly, so you need to get that batter or dough into the oven as quickly as humanly possible. That's why, if you're cooking with and electric oven, it's important to pre-heat it, so you have time to concentrate on the method.
You CANNOT substitute baking soda for baking powder. Why? Like it states above, baking powder has baking soda and other stuff in it. Baking soda is just baking soda. It's the other ingredients in the batter that will kick start the baking soda's leavening process. But if you don't have an ingredient with acidic qualities, it won't work.
Acidic quality ingredients:
- cocoa powder (baking soda turns it red - hence Devil's Food Cake)
- cream of tartar
Is one better than the other? No, they're just different like Uncle Brad.
Parting thoughts: Follow the written recipes when you bake. You're not qualified to pull a "choose your own adventure" stunt and I'm not qualified, or willing quite frankly, to teach you how to do feats and wonders.
The Joy of Cooking - http://www.joyofbaking.com/bakingsoda.html
About.com: Chemistry - http://chemistry.about.com/cs/foodchemistry/f/blbaking.htm