Final answer:
Sulfinic acid (HSO₂H) is a monoprotic acid with only one acidic proton due to the presence of a single ionizable -OH group attached to the sulfur atom. Its Lewis structure reveals the presence of one hydroxyl group (-OH) capable of donating a proton, unlike the hydrogen directly bonded to sulfur, which is not ionizable.
Step-by-step explanation:
Sulfinic Acid and Its Acidic Proton
Sulfinic acid (HSO₂H) is considered a monoprotic acid because it has only one proton (hydrogen atom) that is ionizable and can dissociate in an aqueous solution. To understand why it has only one acidic proton, we need to look at the Lewis structure of sulfinic acid. This acid is monoprotic like other monoprotic acids such as HCl, HNO3, and CH3COOH, where there is only one hydrogen atom attached to a more electronegative atom, making it susceptible to dissociation in water.
In the Lewis structure of sulfinic acid, the sulfur atom is double-bonded to two oxygen atoms and single-bonded to a hydroxyl group (-OH) and a hydrogen atom. This structure clearly shows the presence of a hydroxyl group, which can donate the hydrogen as a proton (H+).
The reason why the other hydrogen atom (attached directly to the sulfur) is not considered acidic is due to its bond with the sulfur atom, which is not as readily ionizable as the bond between the hydrogen and oxygen in the hydroxyl group. In other words, the hydrogen atom in the -OH group is the one that exhibits acidic behavior because the oxygen is more electronegative and can stabilize the resulting anion after losing the hydrogen as a proton.