Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
1. People and Animals
PROJECT: SMOKING HANDS
A few drops of household ammonia
A few drops of muriatic acid (available at hardware stores and swimming pool supply houses)
2 paper towels or cotton balls
Wastebasket or similar container (optional)
See the video at http://youtu.be/i21P1XzoLRE
In the photo on the right, I bring my two bare hands together and press so hard that they start to smoke.
Well, at least it looks like that. What is really going on is a chemical reaction between two vapors.
One vapor comes from dampening my left hand with a little bit of household ammonia. The other vapor comes from dampening my right hand with a little diluted hydrochloric acid, known as muriatic acid. To try this yourself, combine a few drops of muriatic acid with twice as much water in a small bowl to further dilute it. Never use a more concentrated form of hydrochloric acid. Place a few drops of ammonia on a paper towel or cotton ball and wipe it onto your left palm. Use another paper towel or cotton ball to wipe the diluted muriatic acid onto your right palm. You should always wear protective goggles when handling these chemicals— which has the bonus of adding a dramatic sense of danger.
You don’t want to do this unless your hands are free of cuts and scratches, as the hydrochloric acid will sting. But it does not attack the layer of dead skin on your palms, so despite the quite reasonable warnings on the bottle, it does no harm. Of course, it’s also important to wash your hands well after the demonstration. For those who quite sensibly want to avoid putting acid on their hands, the smoke effect can instead be done by placing a few drops of each solution on the paper towels or cotton balls and simply placing them near each other—say, in a wastebasket. Whichever technique you use, be careful to avoid breathing the vapors that result.
What is going on is a fairly simple chemical reaction. The ammonia solution releases ammonia gas (NH3) into the air. The hydrochloric acid releases hydrogen chloride gas (HCl) into the air. The two gases react in the air to produce tiny particles of a white solid called ammonium chloride (NH4Cl).
As we learn more and more about life and about chemistry, the sciences of biology and chemistry have more and more to do with each other.