Question

What is baking powder? How does it make cakes soft and spongy?

Answer 1

Hi, I think it will help u... baking powder is a dry chemical leavening agent . a mixture of carbonate and bicarbonate and a weak acid . it is used for increasing volume and lightning the texture of baked goods. baking powder is mixed with flour and when water is added to make dough baking powder undergoes chemical reaction during which carbon dioxide is produced . this carbon dioxide gas gets trapped in the dough and bubbles out which makes the cakes soft and spongy.

Answer 2

Baking soda has only one ingredient: sodium bicarbonate. That’s it. There’s nothing else in there. You might  remember from grade school science that when you mix baking soda with vinegar you get an eruption. That “eruption” is lots of carbon dioxide bubbles that form when sodium bicarbonate reacts with vinegar. Vinegar isn’t the only thing that baking soda reacts with. Baking soda is a base, so it also reacts with things like buttermilk, yogurt, brown sugar, lemon juice, molasses, and applesauce (anything that is acidic). Once the baking soda reacts with the acidic ingredient, it forms those carbon dioxide bubbles.  
Its all from the carbon dioxide. When a liquid of any kind comes in contact  with the baking soda it releases the carbon dioxide which makes the bread rise since the chemical reaction creates air bubbles. There is special items put in baking powder to do that. If u don't add it, the cake is hard and rocky. carbon dioxide gas is produced when baking powder NaHCo3 is heated in the oven ,this gas evolution makes the cake spongy and soft.