What is the formula for rubbing alcohol?
How does it kill germs?
Is rubbing alcohol the right kind of alcohol or another kind (denatured?)?
Obviously I don't know a heck of lot about this stuff; I'm willing to learn.
Thank you in advance

Rubbing alcohol is generally isopropyl alcohol, whose formula is (CH₃)₂CH₂OH, mixed with water, although there may be other ingredients.

The alcohol we drink is ethanol (CH₃CH₂OH). Denatured alcohol is ethanol with some poisonous substance added. The poisonous substances are added to keep people from drinking it.

I believe rubbing alcohol works by denaturing protiens in the bacteria. Proteins function largely because of their shapes, but things like heat and alcohol can cause their shapes to change, and make them stop functioning. Hopefully someone can tell you with more certainty whether this is really how rubbing alcohol works.

Methos, as usual, is quite right about the mechanism by which alcohol works:

quote:

Alcohol is an antiseptic, which is routinely used to swab the skin prior to an injection. Alcohol acts to coagulate the protein in bacteria. The irreversible change in the protein is lethal to the bacteria. In the example of the injection, alcohol swabbing of the injection site will kill the bacteria on the skin, so that living bacteria are not carried into the body upon insertion of the needle. Dilution of alcohol, so that a solution is 30% alcohol by volume, makes this antiseptic even more potent, as it allows the alcohol to permeate into the bacteria. Pure alcohol rapidly coagulates surface proteins, producing a coagulated crust around the bacteria.

Source.

Note that in decades past (when I was a lad) "rubbing alcohol" was usually ethanol rather than isopropanol.

When I was a lad I learned somewhere that denatured alcohol was poisoned as methos says to keep people from drinking it - that was during prohibition and alcoholics would drink anything alcoholic - the poisonous additive was methyl hydrate.

I'm really surprised, profesor; drug stores sell isopropyl alcohol in two different dilutions, 70% and 90% I think, have I been wasting money on the higher strength, more expensive stuff, thinking it more effective in killing bacteria even deader!

Thanks, Prof.

To head off any confusion, I should point out that I've used the word denatured in two slightly different senses here. In both cases, it refers to changing the 'natural' state - making alcohol undrinkable or making proteins misshapen.

Frank: I, too, was surprised to see that the addition of water to alcohol improves its effectiveness as an antiseptic. Absolute (100%) alcohol is hard to find and expensive, so it's good to know I'm not really missing much.

methos: I know that the complex 3-dimensional shapes of a protein depends on how it folds up according to the charge distribution along its sequence of amino acids, which in turn depends on pH and other factors. Do you suppose that alcohol makes a protein fold up differently ("denature") by displacing water from its normally aqueous environment, thereby changing its charge distribution?

Despite knowing some chemistry I never seem to have a handle on how to apply what I think I know.

Professor - More or less, but it is not as much charges as polarity.

For any observers, polarity is sort of like a partial charge. A molecule can be neutral overall but have some atoms that are slightly positive and others that are slightly negative. Molecules like that, such as water, are called polar molecules.

Other molecules don't have this property- they are neutral throughout. Molecules like this, such as oil, are called nonpolar.

The rule is like dissolves like. Water dissolves in water, and oil in oil, but water and oil don't dissolve in each other. It's slightly more complicated than that, though. There are differnt degrees of polarity.

Gettting back to proteins... Proteins have polar and nonpolar parts, and fold so that the polar parts interact with other polar parts and the nonpolar parts interact with other nonpolar parts. And, part of the protein of course has to be on the outside interacting with the solvent. Alcohol is less polar than water, so these interactions, and therefore the protein shape, will be different.

Putting the protein back into water won't restore its shape, however. The form a protein naturally has isn't necessarily the ideal (in terms of there interactions) form. It is just that the protein would have to go through a less ideal shape to get to the ideal shape. Once denatured and then put back into water, it will settle into a differnt local minimum, from which it would have to pass through a less ideal shape to get back to the original shape.

Hi, thank you everybody for lots of information.
My reasons for asking about alcohol is a diabetic going onto injections. I am in favor of using the STERILE alcohol wipes (tinfoil packages) instead of a bottle and cotton. Actually "Dollar stores" sell bottles of 50% alcohol at "2 for 1$". I need convincing reasons that the wipes are the better thing to use. Are they?