Can you sustitute bi carb soda for baking powder?

Yes, you can substitute bicarbonate of soda (baking soda) for baking powder, but you'll need to adjust the recipe. Baking powder contains both an acid and a base, while baking soda is purely a base. To use baking soda instead, you should add an acid (like vinegar or lemon juice) to the recipe to activate it, typically about 1/2 teaspoon of acid for every 1/4 teaspoon of baking soda used. Keep in mind that you'll need to use less baking soda than the amount of baking powder called for.