Baking Powder & Baking Soda
Baking soda is also known as bicarbonate of soda. These two are the same product – different names in different countries. It is a chemical leavening agent that is used in baking, but it needs some form of acid to activate it.
If you are making a mixture that has acidic ingredients in it, you won’t need to add anything extra to activate the soda. However, if it doesn’t have an acidic mixture, you will need to add cream of tartar or lemon juice to aid the baking soda (5 g of baking soda would require 2 tsp of lemon juice or 2½ tsp of cream of tartar).
Baking powder is a complete leavening agent. It is essentially the baking soda/bicarb of soda with the acidic already added.
If you are unsure if your batter or dough is acidic enough for the baking soda to work without additional acid, then use baking powder.
Chocolate and cocoa is acidic enough for the baking soda to work, but Dutch cocoa has been alkalised, so it does NOT work with baking soda. Other acidic mixes include yoghurt, sourdough, fruit juices, vinegar fermented milks and brown sugar.