Baking soda and baking powder are both leavening agents,

What it is: A pure chemical compound, sodium bicarbonate, that needs an acid (like vinegar, lemon juice, buttermilk, or yogurt) to activate it.
How it works: When baking soda comes in contact with an acid and moisture, it produces carbon dioxide gas, which makes the dough or batter rise.
Use it when: The recipe contains an acid (like lemon, vinegar, buttermilk, etc.). It neutralizes the acid and helps your batter rise.
Important: Baking soda requires a quick reaction. If you don't bake it right away after mixing, it will lose its leavening power.

What it is: A mixture of baking soda, an acid (usually cream of tartar), and a starch (like cornstarch).
How it works: It’s a complete leavening agent because it already contains both an acid and a base. It releases carbon dioxide when mixed with liquid and when exposed to heat, so it doesn’t need an external acid to activate it.
Use it when: Your recipe doesn’t contain any acidic ingredients. It’s perfect for things like pancakes, cakes, and muffins where you need consistent rising without the need for an acid.
Types of baking powder:
- Single-acting: Reacts once when mixed with liquid.
- Double-acting: Reacts twice—once when mixed with liquid and again when exposed to heat. This is the most common type.

Baking soda needs an acid to activate, while baking powder contains both an acid and a base.
Baking soda is typically used when the recipe already has acidic ingredients; baking powder is used when there are no acidic ingredients.
Baking soda is stronger, so it’s usually used in smaller amounts than baking powder.