Baking powder and baking soda are NOT THE SAME. They can not be substituted for one another. They are both leaveners but they are chemically different.
Baking soda is used in recipes that contain acidic ingredients like buttermilk, brown sugar, yogurt, lemon juice, honey, vinegar, or chocolate (except Dutch process). The acid in the recipe reacts with the baking soda, allowing your baked goods to rise. Baking powder is generally used when there is no acidic ingredient in the recipe. Bottom line: baking soda needs an acid; baking powder does not. – Jenny Jones