What is the molecular weight of methanol?

Methanol, also known as methyl alcohol, is an organic compound with molecular formula CH4O or CH3-OH.

It is simplest aliphatic primary alcohol. Methanol is a colorless, inflammable and poisonous liquid.

However, to determine the molecular weight of methanol, first we have to know the molecular formula of the methanol molecule.

Then the number of different atoms in a molecule of methanol has to be determined. Besides, we need to know the atomic mass of different atoms.

This is because the summation of atomic mass of atoms present in a methanol molecule is the molecular weight of methanol.

Read more : What is methanol or methyl alcohol?

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What Is Molecular Weight Or Molecular Mass?

The summation of atomic mass of atoms present in a molecule of a compound is the molecular weight or molecular mass of that compound.

There are three scale for determination of molecular weight or molecular mass, namely carbon scale, hydrogen scale and oxygen scale.

According to carbon scale, the mass of a molecule of a compound is as much as the mass of an atom of carbon C-12, that number is called the molecular mass of that compound.

Structure of methanol

Molecular weight determination and many others analysis show that the molecular formula of methanol is CH4O.

That is, methanol contains one carbon atom, four hydrogen atoms and one oxygen atom.

Assuming that carbon atom is tetra valent, oxygen bivalent and hydrogen univalent, only one structure is possible which is shown.

The above chemical formula as well as structure of methanol is supported by all the chemical reactions of methanol.

For example, only one hydrogen atom in methanol is replaced by sodium. This suggests that one hydrogen atom is in a different state of combination from the other three.

Methanol is formed from methyl chloride by hydrolysis with NaOH. Methyl chloride can have only the structure CH3-Cl.

This means that the methyl group in methyl chloride is unchanged by the action of dilute alkali, and that the reaction takes place by the replacement of the ‘Cl’ atom by a –OH group.

Now, the presence of –OH group is confirmed by the reaction between methanol and PCl5, when CH3-Cl, HCl and POCl3 are formed.

Thus one oxygen atom (bivalent) one hydrogen atom (univalent) have been replaced by one chlorine atom (univalent).

This implies that the oxygen and hydrogen atoms exist as a univalent group in methanol.

Methanol molecular weight

From the above experimentally discussion, it is clear that methanol contain one carbon atom, four hydrogen atoms and one oxygen atom in its single molecule.

According to definition, the molecular weight of methanol is the summation of atomic weight of carbon, hydrogen and oxygen atoms.

Now the atomic weight of carbon atom, hydrogen atoms and oxygen atom from their mass diffraction literature value are 12, 1.01 and 16 respectively.

Therefore, the molecular weight of methanol should be [12 + 4 x 1.01 + 16]. That is, [28 + 4.04] = 32.04.

Hence from the above calculation, it has been found that the exact molecular weight of methanol is 32.04. That is 32.04 g/mol.