Baking soda and baking powder at some points have certain similarities, but in fact they are chemically different products and because of that you need to differentiate them, especially when using them in various recipes. They can be both added in a same recipe, but there is a difference between them. Here it is what makes them different from one to another.
This product is in fact a combination of various acids such as baking soda, cornstarch, and cream of tartar.
During the cooking process the first rise of the dough is when baking powder gets wet and the second one when the baking powder gets heated. Here it is the best ratio: 1 teaspoon f baking powder to a cup of flour.
Baking soda is recognized by other names as well like sodium bicarbonate or bicarbonate of soda. This product is a base mineral which forms carbon dioxide when combined with acidic ingredients.
Therefore, when you use it in recipes it is commonly in a combination with something acidic such as lemon juice, yogurt, buttermilk, brown sugar, molasses, or cream of tartar.
This product is stronger than baking powder, and if it does not get neutralized, it will provide you with that metallic taste. Here is the rule for baking soda in recipes: a quarter teaspoon of baking soda to a cup of flour.
There are recipes that require the presence of both ingredients. The reason for that is keeping balance because the carbon dioxide created from baking soda and certain acid does not leave the volume.
Both products come with an expiration date; hence you need to use them while they are still fresh. You should check the expiration date on the package, or simply perform a test.
Here it is how to test the freshness of baking soda: in a small bowl mix 3 tablespoons of white distilled vinegar with half a teaspoon of baking soda. If the mixture quickly produces bubbles, then this means that the baking soda is fresh.
Use both products fresh, and make certain to change them at least every three months.