Solubility of methanol, the lightest alcohol. Alcohols are categorised by their functional -OH (hydroxyl) group. This functional group is highly polar and allows the alcohol to form strong intermolecular forces with other polar molecules, such as water. Here, methanol (CH3OH) is added to distilled water. Due to its low molecular size and highly polar hydroxyl group, the methanol molecules readily form strong intermolecular hydrogen bonds with polar water molecules. This produces one immiscible layer as the two liquids are mixed. See clip K004 1197 for the same process with a heavier alcohol, hexanol.