How are baking powder and baking soda different?
Both of them are baking soda, which is a chemical that makes
baked foods light and fluffy when it comes into contact with acid
in the food. Baking powder, which contains an acid, is used when
the food doesn't have enough acid to activate the baking soda.
It's not recommended, but I've used baking powder in recipes
that called for baking soda and it worked well. The opposite is not
true--if the recipe calls for baking powder, there's not enough
acid in there to kick off baking soda and eating the product will
be like chewing on a rock.