There isn't a true "substitute" for baking soda in the sense that it will always provide the same leavening power. Baking soda relies on an acidic reaction to release carbon dioxide, which makes baked goods rise. Here's a breakdown of options and why they work differently:

For leavening:

* Baking powder: This is the closest substitute. It contains baking soda, an acid, and a drying agent. It's pre-activated, meaning it works in both acidic and neutral recipes. The ratio is usually 1 teaspoon of baking powder for every 1/2 teaspoon of baking soda.

* Cream of tartar: This is an acid that can be used in combination with baking soda, but you'll need to add more of it than you would baking soda.

* Vinegar or lemon juice: These acids can be added to recipes that contain baking soda to activate it. You'll need to add about 1/4 teaspoon of acid for every 1/2 teaspoon of baking soda.

For other baking soda functions:

* Sodium bicarbonate: This is the chemical name for baking soda. It can be used in some instances, like cleaning, but not for baking.

Important Considerations:

* Recipe adjustments: When substituting baking soda, you need to adjust other ingredients in the recipe (like the amount of liquid) to compensate for the changes in leavening power.

* Flavor: Some substitutes can change the flavor of your baked goods. For example, using vinegar or lemon juice can add a tangy flavor.

* Texture: The texture of your baked goods may also change when you substitute baking soda. For example, using baking powder can result in a more tender texture.

It's best to test a recipe with a substitute before baking a large batch to make sure you like the results.