What is in baking soda that makes it react to vinigar?

Sodium bicarbonate, the chemical name of baking soda, is an alkali, which reacts with the acid vinegar, to neutralise the 2 chemicals

Or, if you want to get technical..... Sodium Bicarbonate (chemical NaHCO3) combines with the dilute Acetic Acid in vinegar, (chemical CH3COOH) to form Sodium Acetate, Water and Carbon Dioxide gas. The gas is released in the form of small bubbles. If the mixture is strong enough and warm enough, it fizzes rapidly. NaHCO3 + CH3COOH → CH3CO2Na + H2O + CO2 (gas) in other Words the the salad dressing (vinegar) and the powdery stuff (baking soda) explode when they touch each other