What is baking soda used for, and how much should be added? 
Baking soda is used in cooking for two purposes:   As a leavening agent, in order to make baked goods rise.  It does this by reacting with acids in the batter or dough, and producing carbon dioxide gas. To soften beans during cooking, particularly chickpeas. The alkalinity of the soda helps the complex carbohydrates and fiber in some types of beans break down, allowing them to puree more smoothly.    I can't answer "how much is added" unless I know what you're making. 