Science of Gastronomy: Baking Soda vs Baking Powder

Baking powder and baking soda are leavening agents. Leavening agents form air bubbles inside cakes and breads thus making them spongy and soft.

Both of them contain sodium bicarbonate. Both of these rely on chemical reactions between acidic and alkaline compounds to produce carbon dioxide to  inflate dough or batter.

Baking soda:

• Contains only alkaline compound.
• When baking powder is added to water it dissolves completely. No bubbles are seen because of absence of acid in plain water.
• Can be added to dough only if the dough or batter contains acid for it to react to. 

Baking powder:

• Has both alkaline and acid compounds. Baking powder = Baking soda + Acid solids.
• When baking powder is added to water it dissolves immediately and tiny bubbles may be seen because of the acid reacting with water.
• Self raising. Does not need an acidic medium for it to work.