What is Absolute Alcohol? - Preparation & Uses

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

The focus of this lesson will be on the organic compound ethanol. Our primary points of discussion will be on how absolute ethanol is obtained and how it is utilized in the lab setting as well as in everyday life.

Old Tennessee Moonshine

Have you ever looked back on America's history to the days of Prohibition? These were the days when the production, sale, and importation of alcoholic beverages was illegal in the United States. During this particular time period people would secretly make and distribute what was called moonshine, or clear whiskey in remote locations so as to not get caught. Moonshine refers to distilled 'spirits' that have a very high alcohol content.

Even though the old Tennessee mountain men thought they were doing pretty good at distilling their illegal whiskey, they certainly never came close to what's called absolute ethanol. This refers to pure ethanol with absolutely no water content, thus the name. It's probably a good thing they never got their hands on absolute ethanol, as it would kill you if you consumed it! Although you never want to drink absolute ethanol it certainly has its value, and in this lesson we will be discussing how it's prepared and then some of the more common uses it finds application in.

Preparation of Absolute Ethanol

In general ethanol is most commonly made by the fermentation of sugars by yeast, or by what's called petrochemical processes. The problem though is that this results in an ethanol-water mixture, which is not what we want. We want 100% ethanol with no water present whatsoever (sometimes this is called 200 proof alcohol). It turns out that removing the water impurity from ethanol isn't so trivial, but let's talk about some of the common methods employed to get rid of those pesky water molecules.


Just like in the olden days, distillation continues to be a tried and true method to separate water from ethanol. Distillation is a technique that's used to separate liquids from one another in a mixture and takes advantage of differing boiling points. Let's say for example you were working with a mixture in which one compound's boiling point was 78 degrees Celsius (ethanol) and the other's was 100 degrees Celsius (water). You would heat your mixture and as the temperature reached 78 degrees Celsius, the ethanol would evaporate (boil) and travel up and down a cooling column filled with cold water. The ethanol vapors would condense back to liquid form and you could collect the ethanol in pure form.

Diagram of a distillation setup

Since the boiling point of ethanol and water aren't that different from one another however, many times a salt has to be added to the mixture such as potassium carbonate to help capture residual amounts of water in order to obtain absolute ethanol.

Water Capture by Molecular Sieves

If you've distilled your ethanol-water mixture and you find you still have a small amount of water present, using molecular sieves to remove the last trace amounts of water is a great method to obtain absolute ethanol. Molecular sieves look like little beads that have tiny pores in them and the size of the pore can be varied. You can actually buy molecular sieves in which the pore size is just the right size to let water molecules inside but nothing else. Since water molecules are of a different size than ethanol molecules, the water will go inside the pores and become captured by the sieves. What's left behind is pure ethanol with no water!

Uses of Absolute Ethanol

Now that we know how absolute ethanol is obtained, lets take a look at some of the common applications it finds use in.

Medical Applications

Ethanol is an excellent antiseptic (antimicrobial substance) and has been used for decades in hand sanitizers and medical wipes. Ethanol kills microbial organisms by denaturing their proteins and dissolving their lipids. Have you ever noticed that if you take too much cough syrup you start to feel funny? That's because some of the active components in cough syrup aren't very soluble (won't dissolve) in water so ethanol is used to help with the solvation of these compounds.

Hand sanitizers contain ethanol which acts as an antiseptic.

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