Baking Soda
Baking Soda is chemically known as Sodium BiCarbonate, Na HCO3 In solution with water and in the presence of an acid, such as vinegar (mild acetic acid) or Cream of Tartar (Tartaric Acid), the CO2 portion of the molecule is released as a gas. Baking soda is used in cooking to produce bubbles in a variety of baked goods.
In baking as in chemistry, there has to be acid in the mix to activate the baking soda. In some mixes of foods there are natural acids in the ingredients. In others, acid must be added. Cream of Tartar is called for in recipes that have no other source of producing an activating acid.
Sometimes a recipe will call for Baking Powder instead of Baking Soda. Baking Powder is already mixed with Cream of Tartar at the correct proportion so that it will create bubbles as soon as it is in water.
To read more about Baking Powder and Baking Soda, refer to this site: