It happens to everyone: You make a perfect cake batter, and as you pour it into the pan, realize you forgot the salt. Or your zucchini bread never rose in the oven, resulting in a gluey brick. Baking mistakes happen, and one of the biggest is confusing baking soda with baking powder.
Both white powders are used as chemical leaveners in baking, but they’re far from the same. Baking soda is pure bicarbonate of soda, an alkaline substance that, when combined with an external acid, produces bubbles of carbon dioxide. Those bubbles are what helps cakes rise, but they only emerge in the presence of an acid. Now, lots of baking ingredients are mildly acidic—take honey, brown sugar, and lemon juice—and when baking soda is in a recipe, it’s specifically there to react to that acidity.
Baking powder, on the other hand, is a blend of two chemicals: baking soda and cream of tartar, aka tartaric acid. Baking powder is pH balanced, which means in the presence of water and heat, it’ll produce carbon dioxide bubbles all on its own. Recipe developers take these chemical differences into account, and the two ingredients can’t be substituted for one another, so as you start that baking project, double check that you’re using the right powder for the job.