A lot of students get confused when asked if Methanol is an acid or base. To be honest, it is a tricky question, but to answer it in one line, I would say it is as acidic or basic as water. Such compounds are also called amphoteric compounds as it exhibits properties of both – acids and bases.
CH3OH Acid or Base
Is Methanol basic?
Methanol, having the chemical formula of CH3OH, consists of a methane group and a hydroxyl functional group ( OH). One might argue how an OH group can be considered as a base. But it’s not the hydroxyl group; it is the OH- hydroxide ion that makes the compound a Lewis base.
As per the definition, a compound or molecule that can donate electrons to form bonds is considered a Lewis base. Here in CH3OH, Oxygen has two lone pairs of electrons. These lone pairs of electrons are used by Lewis acids to complete their orbitals. And hence, as it is an electron-rich compound that can donate the electrons to other molecules, it exhibits a property of Lewis Base. When Methanol reacts with other compounds, it dissociates into cation and a hydroxide. And the compounds that show such properties are considered basic.
Is Methanol acidic?
The pKa value for Methanol is 15.5, which is higher than water. pKa value is the constant used in chemistry to measure the number of acidic and basic ions present in the solution. On dissociation, the molecule gives CH3O- and H+ ions. And according to the definition of acids, a compound that willingly loses a proton is considered acid.
However, This alcohol exhibits weak acidic properties because the CH3 group and OH functional group leads to releasing negative ions in the aqueous solution. A compound that can donate protons are considered acids but here in Methanol; as a result, water is a better proton donor, which makes Methanol a weak acid. Hence, Methanol is a weaker acid than water.
The OH functional group gives the properties of the Lewis base, and hence CH3OH has properties of both weak acid and bases.
Acid strength of alcohols in decreasing order:
alkyl->primary alcohols>secondary alcohols>>tertiary alcohols.
Methanol comes under primary alcohols and hence is stronger than secondary and tertiary alcohols but weaker than water.
Concluding Remarks
Looking at all the chemical properties of Methanol and its pKa value, many biochemists consider this molecule amphoteric in nature as it has both basic and acidic properties. Depending upon the type of molecule it is reacting with, it exhibits its acidic or basic property. To answer in a nutshell, Methanol is as acidic and basic as water and is considered a weak acid.
