We run into all these different kinds of alcohol. Let’s look at the differences.
First there’s the alcohol you drink, like whiskey, beer and wine. This is ethyl alcohol that is produced by yeast. The yeast eat some kind of sugar or starch and turn it into carbon dioxide and alcohol. In wine the process is pretty simple – yeast eats the sugar in grape juice and creates alcohol. In whiskey, the alcohol is distilled to get the concentration higher. See how whiskey works for information on distillation.
Ethanol that you purchase as a car fuel is the same kind of alcohol found in whiskey, but it has been distilled to the point where it is nearly pure alcohol (as opposed to whiskey which is typically only 40% alcohol and 60% water). See this page and this page for a quick introduction to ethanol production.
Denatured alcohol – found in bottles at the hardware store or the drug store – is also ethanol. But it has been poisoned to keep people from drinking it. It turns out that ethanol is a good solvent, and also useful as a fuel. And it is pretty cheap to make it. But if you sold ethanol for $2 a gallon at the hardware store, lots of people would be drinking it to avoid the “sin taxes” on beer, wine and whiskey. So they poison the ethanol and sell it without the sin taxes.
Methanol is sometimes found in windshield wiper fluid to keep it from freezing, and it is also used as the fuel for Champ cars and Indy cars. It is sometimes called wood alcohol because it used to be made from wood, but today its made from natural gas. Methanol is poisonous, and it is one of the chemicals that can be used to poison denatured alcohol.
Isopropyl alcohol is a slightly bigger molecule than ethanol (Methanol is CH4O, Ethanol is C2H6O and Isopropyl alcohol is C3H8O) and is often cheaper to make. It is not as poisonous as methanol (an ounce of methanol can kill you and a third of an ounce causes blindness). So it is useful as a solvent in the same way acetone is useful as a solvent. It also burns nicely. We saw isopropyl alcohol being used to make a cloud chamber in this post. It can also be used to make bottle rockets:
Rubbing alcohol is a generic term that can be either denatured alcohol or isopropyl alcohol.
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