Why do alcohols dissolve in water
Alcohols: water solubilityEF
Alcohol and water
Let's compare the ethanol molecule with the water molecule. The ethanol molecule is actually "just" a water molecule in which one hydrogen atom has been replaced by an ethyl group. This explains some of the physical properties of ethanol, for example its extremely good solubility in water or its boiling point of 78ºC, which is quite high for an organic compound.
You can find out more about the physical properties of water on the specially created page "Crash Course Water".
Methanol, ethanol and propanol have unlimited solubility in water. This is because the influence of the hydrophilic OH group is quite great because the alkyl groups are still very small. With the OH group, the alcohols can form hydrogen bonds with one another and of course with water molecules.
Graphic representation of the water solubility of alkanols
Butanol is also soluble in water, but no longer indefinitely. Only up to 77 grams of butan-1-ol can dissolve in 1 liter of water. In the case of pentan-1-ol, the solubility in water is only 22 g / l. Hexan-1-ol dissolves at 5.9 g / l in water, heptan-1-ol at 1.0 g / l. The longer the alkyl chain of the alkanol, the lower the water solubility. In the case of even longer alkanols, virtually no water solubility can be demonstrated.
YouTube video "Solubility of various alcohols"
In the YouTube video "Solubility of various alcohols" you can see a very nice experiment on the water solubility of ethanol, propanol, butanol and heptanol. However, the second part of the video, in which the attempts are explained, is far too quiet, which is a shame, as the explanation itself is very good.
In September 2019 I carried out a series of tests on the water solubility of alcohols with my chemistry GK level EF. The results of this experiment can be found on this extra page.
The hydroxyl group determines the physical properties of the alkanols, including the water solubility. In itself, a hydroxyl group leads to very good solubility in water because the OH group can form hydrogen bonds with the water molecules. However, the larger the alkyl group of the alcohol, the less the influence of the OH group, and the hydrophobic character of the alkyl group then predominates.
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