That’s chemistry: The science behind alcohol

Pint of beer on a wooden table

Source: ljubaphoto / iStock / Getty Images Plus

That’s alcohol isn’t it?

Strictly, ‘alcohol’ means a family of compounds with the –OH functional group, of which ethanol is just one. The first part of the name tells you how many carbons there are in the molecule, just as in alkanes, the ending indicates the presence of the –OH group. Ethanol is the alcohol found in alcoholic drinks.

Is it safe to drink?

No. Ethanol is a drug, and if you drink a few hundred millilitres of the pure substance, it can be fatal. Alcoholic drinks are dilute in pure ethanol – spirits may contain 30–40 per cent ethanol by volume, wines 10–14 per cent and a regular beer 4–5 per cent. In an episode of the BBC school drama Waterloo Road, aired in November 2009, students stole ethanol from the science lab and used it to make homemade cocktails which they sold to other students. The result being one barely conscious student was rushed off to hospital apparently suffering from alcohol poisoning.

Was the drink too strong?

Yes, that’s very likely but there is an even more serious health issue. Methanol (CH3OH), another alcohol, is often added to ethanol to make it undrinkable – this mixture is known as industrially denatured alcohol. When schools need ethanol for experiments, it is sold to them as industrially denatured alcohol by a specialist chemical supplier, under licence, and must be stored under lock and key. This is probably the stuff that the students used to make the bootleg drinks.

Why does methanol make ethanol undrinkable?

Because it’s more toxic than ethanol. In our bodies ethanol is broken down by enzymes in the liver, which catalyse its oxidation to the aldehyde ethanal which is further oxidised to ethanoic acid. The body then breaks the acid down into CO2 and H2O. Ethanal is more toxic than ethanol and is in part responsible for the symptoms of a hangover.

Methanol is processed in a series of analogous reactions resulting in more toxic products (methanal, HCHO, and methanoic acid, HCO2H) that can attack the human optic nerve and cause blindness. A lethal dose of methanol can be as little as 30 ml.

This article was originally published in InfoChem