Put the salt and vinegar in the bowl. Stir until the salt dissolves.
Dip one penny halfway into the liquid. Hold it there for about 10 seconds, then pull it out. What do you see?
Dump all the pennies into the liquid. You can watch them change for the first few seconds. After that you won’t see anything happen.
After 5 minutes, take half of the pennies out of the liquid. Put them on a paper towel to dry.
Take the rest of the pennies out of the liquid. Rinse them really well under running water, and put them on a paper towel to dry. Write “rinsed” on the second paper towel.
Put a nail and a screw into the liquid. Lean another nail against the side of the bowl so that only part of it is in the liquid
After 10 minutes, take a look at the nails. Are they a different color than they were before? Is the leaning nail 2 different colors? If not, leave the nails in the bowl and check on them again in an hour or so.
What’s happening to the screw? You may see lots and lots of fizzing bubbles coming from the threads. Is the screw changing color? Leave it in the liquid for a while and see what happens.
After about an hour, look at the pennies on the paper towels. What’s happened to the ones you rinsed? What’s happened to the others? What color is the paper towel under the unrinsed pennies?