Solubility of alcohols (eg. ethanol)

In case of alcohols, just as it happens in case of many other biological molecules, the basic solubility rule that like dissolves like is a bit more complexed. Each alcohol consists of a carbon chain (always nonpolar) and a OH group (which is polar). For ethanol for example the chemical formula looks lie this: C2H5OH. Ethanol has a 2 carbon chain and a OH group. As water is polar it attracts OH group. Carbon chain on the other hand as nonpolar is repelled. Solubility of alcohols is therefore determined by the stronger of the two forces.

Because of the strenght of the attraction of the OH group, first three alcohols (methanol, ethanol and propanol) are completely miscible. They dissolve in water in any amount. Starting with the four-carbon butanol the solubility of alcohols is starting to decrease. After the 7-carbon heptanol, alcohols are considered immiscible. The alcohol solublity in water can be observed below. The amounts are in mol/100g of H2O at 1atm and 25oC.

Alcohol solubility chart

Name Formula Solubility
Methanol CH3OH miscible
Ethanol C2H5OH miscible
Propanol C3H7OH miscible
Butanol C4H9OH 0.11
Pentanol C5H11OH 0.030
Hexanol C6H13OH 0.0058
Heptanol C7H15OH 0.0008