baking soda vs. baking powder

Baking powder is a mixture of cream of tartar, baking soda, and sometimes a starch. This mixture balances out the effects of the soda, which is very strong and makes the cake rise and bubble as it bakes by releasing gases. The cream of tartar and starch stabilize the reaction so it doesn't puff too much, and tastes milder. If you just use baking soda, the crust will be affected differently, and it will taste much more salty, sometimes bitter.

If you use baking soda instead of baking powder as instructed in a recipe, your cake would taste different because baking soda has a much stronger taste than baking powder. That is my experience.

According to a few websites, baking soda & baking powder are interchangeable, but they are not equal. The problem is, I'm getting different info from various sites. Some say baking powder is stronger than baking soda, while other sites say the opposite. Most seem to agree, though, that if the recipe says use baking powder, you have to replace it not only with baking soda, but to also include cream of tartar & some include cornstarch.