This Week's Experiment - #213 Peroxide Bubbles
This week's experiment comes from some gardening that we did on this rare
weekend at home. I installed an automatic watering system, so all of Lisa's
flowers will survive while we are on the road. As it is underground, it
should also save a lot of water, keeping it where we want it with a minimum
of evaporation and runoff. I also removed a lot of weeds and reworked some
of the flower beds. I was moving a couple of small palm trees and managed to
scratch my hands a bit. As I was cleaning the scratches, I thought that it
would make a good experiment. You will need:
3% hydrogen peroxide (from the grocery or pharmacy)
your hand
a potato
Hydrogen peroxide is one of those magical cures that many adults remember
from their childhood, and we pass it along to our kids. If you get a cut or
scratch, you put some peroxide on it. You can tell if the cut has germs,
because then it will bubble, right? Well, that is what we are told, but as
we will see, things are not always as they seem.
Lets start out with your skin. Are there any germs on your skin? Look
closely. Do you see them? No. Are they there? Yes, they are. No matter
how much you wash your hands, no matter how much you scrub, you have bacteria
and other things living on your skin. Since there are germs on your skin, it
should bubble if you put some hydrogen peroxide on it, right? Try it and
see.
Did you get any bubbles? Probably not, unless you have a cut or scratch.
What makes the bubbles is not the presence of germs. Instead, it is the
presence of a substance called catalase. This is a chemical that is found in
your blood and in the cells of your body. To see this, we don't have to use
your blood. Luckily, it is also found in potatoes. If you cut a slice of
potato and put some peroxide on it, it will bubble. When a cut bubbles, it
does not mean that it is infected. It just means that it has either some
blood or some damaged cells. This brings the hydrogen peroxide in contact
with catalase and you get bubbles.
OK, then what causes the bubbles? Hydrogen peroxide is chemically very
similar to water. Where the chemical formula for water is H2O, hydrogen
peroxide is H2O2. The H stands for an atom of hydrogen and the O stands for
an atom of oxygen. A molecule of water contains two atoms of hydrogen and
one atom of oxygen. The only difference between hydrogen peroxide and water
is a little oxygen. That may not sound like much of a difference, but it is.
In chemistry, things can change a lot when you change the formula. Adding
oxygen to iron gives you rust. The soft, reddish rust is very different from
a piece of iron metal. An extra atom of oxygen also makes hydrogen
peroxide a very different chemical, which can be dangerous if it is
concentrated. That is why the stuff you get at the grocery is only 3%. The
rest is plain water and it is diluted enough to make it safe for household
use.
Left to itself, hydrogen peroxide will slowly lose the extra oxygen and
change into water. Certain chemicals will speed up the reaction, causing the
extra oxygen to be freed very quickly. Catalase is one of those chemicals.
But why would that be a good thing? In high concentrations, oxygen is
poisonous to some germs. The idea is that you get a lot of oxygen into the
cut, to kill these germs. Then a scab forms, keeping any more germs from
getting into the cut. Looking online, there seems to be a lot of debate over
how effective hydrogen peroxide is for treating cuts. Some sources say that
it is very useful. Others say that it does not do more than soap and water,
and some say that it actually causes more harm than good. The majority say
that it is at least as useful as soap and water, so I will continue to use
it. Besides, it is still amazing to see a cut bubble and foam as you clean
it.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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