Baking soda can be substituted for baking powder as long as an acidic ingredient is used in the recipe. Baking soda is four times stronger than baking powder, so the substitution will not be an identical measurement. If a recipe calls for a teaspoon of baking powder, use only 1/4 teaspoon of baking soda.
The activation of baking soda is a result of the sodium bicarbonate mixing with an acidic ingredient. The chemical reaction causes a recipe to rise and produce a nice texture while baking. Common acidic ingredients used in baking include buttermilk, yogurt, and lemon juice. Another useful baking powder substitute is a mix of baking soda and cream of tartar. This combination is almost an exact replacement.
While baking soda can be a good substitute for baking powder, it is not recommended to substitute baking powder for baking soda.