Question

What is the difference between baking soda baking powder?

Answer 1

Baking soda has only one ingredient: sodium bicarbonate. Sodium bicarbonate is a base that reacts when it comes into contact with acids, like buttermilk, yoghurt or vinegar. This reaction produces carbon dioxide $\left(C{O}_2\right)$ in the form of bubbles, like a liquid foam.

When making baked goods, the process is called “chemical leavening,” because the trapped $\left(C{O}_2\right)$ gas makes the dough or batter rise.

But when baking soda comes into contact with an acid, it pretty much reacts immediately.

For many baking recipes, you want an extended reaction, so that the rising doesn’t take place all at once.
Baking powder addresses this problem because it is “double acting” – it has different ingredients that create $\left(C{O}_2\right)$ gas at different stages of the baking process.

All baking powders contain sodium bicarbonate (just like baking soda). But baking powder also contains two acids. One of these acids is called monocalcium phosphate. Monocalcium phosphate doesn’t react with the sodium bicarbonate while it’s dry. But as soon as the baking powder is stirred into a wet dough or batter, the two ingredients begin to react, releasing bubbles of $\left(C{O}_2\right)$ and causing chemical leavening.

But to extend the chemical leavening process, the baking powder also contains a second acid, either sodium acid pyrophosphate or sodium aluminium sulphate. Neither of these acids reacts with sodium bicarbonate until they are both: wet (i.e., stirred into the batter) and hot.