The Citric acid and Tartaric acid are weak
acids. That is why they are safe to eat.
When dry, they are not able to react with other
substances. But when wet with your saliva or spit, they taste sour and
react with the baking soda.
Baking soda reacts with the acid and gives off
carbon dioxide gas. Vinegar contains another food acid; Acetic acid.
You might be surprised to learn that your stomach
contains a very powerful acid, called Hydrochloric Acid (HCl). Your
body uses this to help dissolve and breakdown food into very small
particles so your body can use it. See if you can find out why it
doesn't dissolve you!