Baking powder is used in baking to make cake batter and bread dough rise. The big advantage of baking powder over yeast is that it works instantly. Here's how the chemical reaction in baking powder works.
Baking powder contains baking soda (sodium bicarbonate) and a dry acid (cream of tartar or sodium aluminum sulfate). When liquid is added to a baking recipe, these two ingredients react to form bubbles of carbon dioxide gas.
The reaction that occurs between sodium bicarbonate (NaHCO3) and cream of tartar (KHC4H4O6) is:
NaHCO3 + KHC4H4O6 → KNaC4H4O6 + H2O + CO2
Sodium bicarbonate and sodium aluminum sulfate (NaAl(SO4)2) react in a similar manner:
3 NaHCO3 + NaAl(SO4)2 → Al(OH)3 + 2 Na2SO4 + 3 CO2
USING BAKING POWDER CORRECTLY
The chemical reaction that produces the carbon dioxide bubbles occurs immediately upon adding water, milk, eggs or another water-based liquid ingredient. Because of this, it's important to cook the recipe right away, before the bubbles disappear. Also, it's important to avoid over-mixing the recipe so that you don't stir the bubbles out of the mixture.
You can buy single-acting or double-acting baking powder. Single-acting baking powder makes carbon dioxide as soon as the recipe is mixed. Double-acting powder produces additional bubbles as the recipe is heated in the oven.
Double-acting powder usually contains calcium acid phosphate, which releases a small amount of carbon dioxide when mixed with water and baking soda, but much more carbon dioxide when the recipe is heated.
You use the same amount of single-acting and double-acting baking powder in a recipe. The only difference is when the bubbles are produced.
The double-acting powder is more common and is useful for recipes that might not get cooked right away, such as cookie dough.