Why is ethanol less dense than water

Ethyl alcohol is the main component in denatured alcohol (Swiss "denatured alcohol"). In both cases it is a highly flammable liquid. When decanting, vapors are released which, together with air, form an explosive mixture. Open flames or hidden embers can ignite this mixture. The resulting jet flame or deflagration can lead to serious burn injuries. Denatured alcohol must never be used to fire up the charcoal grill. In the laboratory, ethyl alcohol is always heated in a water bath. When distilling alcoholic beverages in the school laboratory, ensure that the room is well ventilated; alcohol should never be poured near a flame. Bottles and vessels are closed immediately after each removal. The use of the outdated wick burner is strongly discouraged due to the high risk potential: The alcohol can start to boil in the reservoir due to its own heating, which creates a meter-high jet flame. It is mandatory to wear protective goggles when working with ethyl alcohol and denatured alcohol.

Effect on the human body

Pure, one hundred percent ethyl alcohol smells spicy, tastes burning and has a germicidal effect. In a diluted form, it is consumed in alcoholic beverages. If fermentations are not carried out carefully, the toxic methyl alcohol can also be produced in addition to ethyl alcohol. However, this is unlikely to be found in commercially available alcoholic beverages.

If ethyl alcohol is ingested through alcoholic beverages, it enters the bloodstream via the digestive organs. Since it is soluble in both fat and water, it goes particularly easily into the fat-rich brain and nerve cells, where it causes stimulating in small doses and anesthetic-like symptoms in high doses. It has a pain-relieving effect and reduces the ability to react. Your own performance is overestimated, so driving a car while intoxicated is associated with great risks. The use of alcohol in connection with medication is particularly dangerous. Prolonged consumption of alcohol in higher concentrations can lead to addiction. Because alcohol is broken down in the liver and kidneys, it causes severe liver and kidney damage. The liver becomes fatty or the kidneys shrink. Alcohol also kills the nerve cells in the brain.

"Promille Tester" for measuring the air you breathe.

Ethyl alcohol is found in low concentrations not only in alcoholic beverages, but also in various foods. Apple juice can contain up to 0.4 percent alcohol by volume. But it is also found in grape juice, sauerkraut, bananas, kefir and white bread.

foodAlcohol content, Volume percent Luxury foodsAlcohol content,
Volume percent
loaf0 to 0.3%Beer export / pils4.5 to 6%
Apple juice0 to 0.4%Strong beer6 to 12%
Alcohol-free beer0 to 0.5%Must4 to 8%
sauerkraut0 to 0.5%Wine / sparkling wine8 to 14%
Grape juice0 to 0.6%liqueur15 to 40%
Bananas0 to 1%spirits37.5 to 80%
kefir0 to 1%rum60 to 80%

Alcohol in Pregnancy and Effects on Young Children

If a pregnant woman drinks even small amounts of alcohol, this, together with its toxic breakdown product acetaldehyde, reaches the fetus directly via the placenta. This cannot break down the alcohol itself. The alcohol wreaks havoc in the unborn child in the brain and other organs. Malformations can occur. Children born with fetal alcohol syndrome (FAS) show mental, motor, and behavioral developmental disorders after birth. Such children run the risk of developing alcohol addiction more often later on. There is also a considerable risk after the birth if parents are not informed accordingly: Small amounts of alcohol - such as those found in natural apple juice concentrate, for example - have a highly toxic effect on smaller children, as the liver only gradually develops the enzymes necessary for breakdown .

Chemical-physical properties

Ethyl alcohol is a highly flammable, hygroscopic, highly water-attracting liquid. After lighting with a weakly glowing flame, it burns in the oxygen in the air to form carbon dioxide and water vapor. The flame glows significantly more than the flame that is created when burning methyl alcohol:

Flames when burning methyl alcohol (left) and ethyl alcohol (right).

The alcohol is readily soluble in water and also dissolves most other organic solvents such as diethyl ether, gasoline, benzene or chloroform. When it is mixed with water, there is a contraction in volume and a build-up of heat. 52 parts by volume of ethyl alcohol and 48 parts by volume of water make not 100, but only 96.3 parts by volume of the mixture.

Density in grams per cubic centimeter at 20 ° C

Volume percent ethanol

Density in grams per cubic centimeter at 20 ° C

Weight percent ethanol











Density of ethanol-water mixtures at 20 ° C, sources: volume percent Katmar software, weight percent rounded according to Lide

The approximate density determination is carried out according to the floating method with a hydrometer. The relatively exact measurement can be made in the laboratory with a pycnometer. Ethanol-water mixtures are combustible above a weight concentration of about 40%, which corresponds to about 47 percent by volume. When the ethyl alcohol is oxidized, for example with copper oxide, ethanal is obtained, which can be oxidized again to form ethanoic acid. This acid is also known under the name acetic acid:

If wine is left open in the air for a long time, it tastes sour after a while, the alcohol then oxidizes directly to acetic acid with the oxygen in the air. With alkanoic acids and in the presence of heat and a catalyst such as sulfuric acid, odorous ester compounds are formed. The reaction with acetic acid gives ethyl acetate:

This ester reaction, which is only summarized here, is a reaction mechanism with several intermediate steps, with water being split off at the end and the ester is formed. If ethanol in excess is heated with sulfuric acid to about 130 ° C, diethyl ether is formed. The sea wine reaction also produces water as a by-product:

Polarity of the ethanol molecule

In an experiment it can be shown that magnesium powder can be oxidized to magnesium oxide in pure ethanol vapor. The oxygen atom in the OH group, the hydroxyl group, of the alcohol is responsible for this. It is this functional group that determines the properties of the ethanol. Ethanol is soluble in water and petrol at the same time. The water solubility is due to a charge shift within the ethanol molecule. Due to its high electronegativity, the oxygen atom in the hydroxyl group of the alcohol likes to attract electrons and uses the electrons of the electron pair bonds. This results in a different electron density in the ethanol molecule, so that a charge shift occurs. This effect is called inductive effectThis means that the molecule becomes polar.


Ethanol molecule (left) and water molecule (right).

The water molecule is also polar. If you mix ethanol and water, the opposing charges attract each other. The intermolecular forces of attraction between hydrogen atoms and an electronegative partner are called Hydrogen bonds. The binding forces are drawn with a dashed line:

Hydrogen bonds between the two molecules.

For this reason, ethanol and methanol are very soluble in water. In contrast to methanol, ethanol already has a short carbon chain. As the chain length increases, the inductive effect is canceled out, so butanol is only very poorly soluble in water and the more readily soluble in petrol. The existing short chain in ethanol already enables gasoline solubility.
In alcoholic fermentation, mainly simple sugars such as glucose or fructose - for example from grapes, berries or fruit - are broken down in the presence of yeasts into ethanol and carbon dioxide. The yeasts act as enzymes and enable the biochemical fermentation process:

glucose Ethanol + carbon dioxide

When brewing beer, grain starch is first turned into malt sugar
converted, which then forms alcohol in the fermentation process.

The resulting alcohol product has a maximum alcohol concentration of 18 percent, as the yeast cells perish above this concentration. By subsequent multiple distillation, the so-called "schnapps distilling", an azeotropic alcohol-water mixture with about 95 percent alcohol content is obtained. A pure, anhydrous alcohol can be obtained through renewed distillation and the addition of a dehydrating substance, for example calcined, white copper sulfate or quick lime.

In the case of “schnapps distilling”, an alcoholic drink becomes
Alcohol distilled off. A high-proof drink is obtained.

Industrially, ethyl alcohol can be produced artificially by hydration from ethene. This reaction takes place under heat, high pressure and with the help of phosphoric acid:

Ethyl alcohol is a widespread luxury food in alcoholic beverages. In medicine and pharmacy it is used as an extractant, for tinctures and as a disinfectant. Today's thermometers with red filling contain a colored alcohol mixture as a substitute for the poisonous mercury.

Thermometer with colored, alcoholic filling in yoghurt (left),
alcoholic arnica extracts with (right).

In the paint and varnish industry, ethyl alcohol is a universal solvent for fats, oils and resins. In cosmetic products, it is an important solvent for fragrances, for example in perfumes, aftershave and hair lotion. In denatured alcohol, the ethyl alcohol is made inedible with a denaturant. The sometimes toxic additives contain acetone or methanol, for example, so denatured alcohol must not be drunk. The household alcohol burners for fondue have largely been replaced by burners with a fuel paste. The gel-like fuel paste made from ethyl alcohol is considered safe to handle. It is made from ethyl alcohol and calcium acetate. Denatured fuel is also used as a cleaning agent for cleaning windows.

Denatured alcohol and safety fuel paste.

Bioethanol E85, which is available at various filling stations in Switzerland, is a mixture of 85 percent ethanol and 15 percent unleaded petrol. This ethanol is obtained from renewable raw materials through fermentation, in Switzerland mainly from bio-waste or waste from the wood industry. Bioethanol E85 may only be used in special vehicle engines.

Bioethanol filling station in Winterthur.

The biofuel E10 introduced in Germany and the EU contains up to ten percent ethanol, which is obtained from plants, as an admixture to ordinary gasoline. When it was introduced at the petrol stations, it turned out that the biofuel, despite the high octane number RON = 95, was not accepted by many motorists. A few older vehicles cannot tolerate the biofuel. Corresponding lists of the E10 compatibility of motor vehicles are available, for example, from the Association of the German Automotive Industry.

During the Second World War, ethyl alcohol was used as rocket fuel in conjunction with liquid oxygen in the V2 rocket. Today, in the chemical industry, ethanol is a raw material for many chemicals, for example for diethyl ether, chloroform, ethyl chloride, dyes and medicines.

Further information and media
Distillation as a basic chemical operation
Student exercise: distilling wine
Working with denatured alcohol in the household (including videos)
Digital foils for distillation and alcohol
Student exercises on alcohol
Alcohols as a group of substances in organic chemistry
Information about fermentation processes
Detect oxygen atoms in alcohol molecules

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