Baking soda is a single ingredient, sodium bicarbonate, that requires an acidic ingredient and moisture to activate and leaven baked goods. Baking powder, on the other hand, is a pre-packaged mixture of baking soda, an acid, and a starch (like cornstarch). Baking powder is designed to react with moisture and heat, making it a complete leavening agent. 

Here’s a more detailed comparison:

Baking Soda:

  • What it is: Pure sodium bicarbonate (NaHCO3). 
  • How it works: Reacts with an acidic ingredient (like buttermilk, molasses, or chocolate) and moisture to produce carbon dioxide gas, which leavens baked goods. 
  • When to use it: Recipes that already have an acidic ingredient. 
  • Example: Cookies, cakes, and muffins that use buttermilk or brown sugar as ingredients. 

Baking Powder:

  • What it is:A mixture of baking soda, an acid (like cream of tartar), and a starch (like cornstarch). 
  • How it works:Releases carbon dioxide when mixed with moisture and heat, making it a complete leavening agent. 
  • When to use it:When a recipe doesn’t include an acidic ingredient. 
  • Example:Many recipes where you don’t have an acidic ingredient, such as some cakes and muffins. 

Key Differences:

  • Acid:Baking soda needs an acid to activate, while baking powder already has the acid in its formulation. 
  • Moisture & Heat:Baking soda requires both an acid and moisture, while baking powder needs moisture and heat to activate. 
  • Completeness:Baking powder is a complete leavening agent, while baking soda needs an acidic ingredient to be added. 

In essence: Baking soda is a single ingredient that needs an acid to work, while baking powder is a combination of ingredients that is ready to work with moisture and heat.