Answer: Pantry staples baking soda and bicarbonate of soda are different names for the same thing. In Australia, we mostly refer to it as bicarbonate of soda but overseas - especially in America - it's referred to as baking soda. They aren't interchangeable, but bicarbonate of soda and baking powder are both leavening agents. When included in a batter, the leavening agent causes air bubbles (produced by stirring, whipping or beating to expand when cooked, causing it to 'rise'.
Bicarbonate of soda is a pure leavening agent. It needs to be mixed with moisture and an acidic ingredient for the necessary chemical reaction to take place to make food rise. Because it needs an acid to create the rising quality, it is often used in recipes where there is already an acidic ingredient present, such as lemon juice, chocolate, buttermilk or honey.
Baking powder, which contains bicarbonate of soda, comes pre-mixed with the acidic ingredient for you - so all you need to add is the moisture. The acidic ingredient most often used in baking powder is cream of tartar. You can make your own baking powder: simply mix two parts cream of tartar with one part bicarbonate of soda. Baking powder has a neutral taste and is often used in recipes that have other neutral-tasting ingredients, such as milk.
In Australia, we usually just cook with self-raising flour when a leavening agent is required, unless the specific qualities of bicarbonate of soda are required. Bicarbonate of soda imparts a slightly different quality to that of baking powder when used in cooking. It can have a slightly 'tangy' taste and it makes a lovely golden colour. It also makes a very specific texture not achievable with baking powder. It is very important to sift bicarbonate of soda well as it gets lumpy and to use very exact measures as the 'tangy' taste can quite easily become bitter or soapy if too much is used.