Baking powder and bicarbonate of soda are not the same thing. Although baking powder and bicarbonate of soda are both leavening agents, they are not interchangeable.
Baking powder, which contains bicarbonate of soda, is premixed with an acidic ingredient, such as cream of tartar. Bicarbonate of soda needs to be mixed with moisture and an acid before it will perform the same as baking powder.
Chocolate, lemon juice, honey or buttermilk can be added to one part bicarbonate of soda and two parts cream of tartar to create the chemical reaction that baking powder provides. Using a self-rising flour omits the need for a leavening agent in a recipe.