You've probably been told at some point in your life not to test a 9-volt battery by sticking it to your tongue.
But if you're a rebel and you ignored that sage advice, in addition to the slightly painful shock you received, you might have noticed the battery tasted almost sour, kind of like lemonade.
Thankfully, that flavor wasn't battery acid, it was actually the taste of the electrical current from the charged battery.
When you touch the little knobs or leads of a 9-volt battery on your skin, you don't feel a shock because your skin doesn't conduct electricity well enough for a current to really flow.
When you touch them to your tongue, on the other hand, your saliva has no trouble completing the circuit.
Once this circuit closes, electrons start moving out of one lead and into the other, creating an electrical current.
And on the way, they can interact with the water molecules and basically rip them apart in a process called electrolysis.
Current entering your saliva from one lead creates hydrogen gas, leaving hydroxide ions behind.
And current leaving your saliva through the other lead creates oxygen gas, leaving hydrogen ions behind.
These hydrogen ions are what sour taste receptors in your taste buds pick up on; they're also found in acidic foods.
