what is the difference between baking powder and baking soda?!
Baking power contains baking soda. Baking powder is more neutral (PH wise) and soda is more acidic. Depending on whats in your recipe one will work with the other ingredients better than the other.
Here this sums it up pretty well:
"How Are Recipes Determined?
Some recipes call for baking soda, while others call for baking powder. Which ingredient is used depends on the other ingredients in the recipe. The ultimate goal is to produce a tasty product with a pleasing texture. 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.
Baking powder has baking soda as an ingredient and also contains an acid ingredient (like cream of tartar)
When you combine an acid and an alkaline component and add water (or any liquid), carbon dioxide gas is released. Baking powder contains both. The carbon dioxide gas is what gives the rise to baked goods (just like yeast would)
Many recipes that only use baking soda get the acid somewhere else. For example, Soda bread uses baking soda (alkaline) and butter milk (the acid)
Most baking powder is "double acting", which means it has baking soda with two acids, one fast acting that reacts right away when liquid is added and another heat acting that reacts while it's baking. Recipes that use baking soda for leavening have some other acid for the fast acting reaction, such as buttermilk, cream of tartar, lemon, etc. But these recipes are single acting, so you need to take some care to get them cooking while the reaction is still occuring, or they won't rise well. Baking soda can be used with baking powder in order to react and neutralize other acidic ingredients in the recipe.