Students are often surprised to learn that organic acids, such as acetic acid, contain - OH groups. Actually, all oxyacids contain hydroxyl groups. Sulfuric acid, usually written as \(\mathrm{H}_{2} \mathrm{SO}_{4}\), has the structural formula \(\mathrm{SO}_{2}(\mathrm{OH})_{2}\), where \(\mathrm{S}\) is the central atom. Identify the acids whose structural formulas are shown below. Why do they behave as acids, while \(\mathrm{NaOH}\) and \(\mathrm{KOH}\) are bases? a. \(\mathrm{SO}(\mathrm{OH})_{2}\) b. \(\mathrm{ClO}_{2}(\mathrm{OH})\) c. \(\mathrm{HPO}(\mathrm{OH})_{2}\)

Let's write down the structural formula of each given compound in the standard molecular formula notation. a. \(\mathrm{SO}(\mathrm{OH})_{2}\): Since the sulfur atom here is bonded to two hydroxyl groups, this compound can be written as \(\mathrm{H}_{2}\mathrm{SO}_{2}\). This is known as Sulfurous acid. b. \(\mathrm{ClO}_{2}(\mathrm{OH})\): In this compound, the chlorine atom is bonded to two oxygen atoms and one hydroxyl group. This can be written as \(\mathrm{HClO}_{2}\). It is called Chlorous acid. c. \(\mathrm{HPO}(\mathrm{OH})_{2}\): This compound has one hydrogen atom combined with a phosphorus atom, two oxygen atoms, and two hydroxyl groups. It can be written as \(\mathrm{H}_{3}\mathrm{PO}_{2}\). This is called Phosphorous acid.

Now that we have identified the compounds, let's understand why they exhibit acidic behavior. An acid is a substance that donates a proton (H+) to a base. In the given compounds, the attached hydroxyl groups (OH) can lose a hydrogen ion (H+), causing the substances to act as acids. For example: \[ \mathrm{H}_{2}\mathrm{SO}_{2} \rightarrow \mathrm{H}^{+} + \mathrm{HSO}_{2}^{-}\] Now, let's understand why NaOH and KOH are classified as bases instead.

In contrast to acidic behavior, a base is a substance that accepts a proton (H+). NaOH and KOH are metal hydroxides that dissociate in water to generate hydroxide ions (OH-) and the corresponding metal cations (Na+ or K+). These hydroxide ions can react with and accept H+ ions from an acid, thus exhibiting basic behavior. For instance, NaOH dissociates as follows: \[ \mathrm{NaOH} \rightarrow \mathrm{Na}^{+} + \mathrm{OH}^{-} \]

To summarize, the given compounds are Sulfurous acid (\(\mathrm{H}_{2}\mathrm{SO}_{2}\)), Chlorous acid (\(\mathrm{HClO}_{2}\)), and Phosphorous acid (\(\mathrm{H}_{3}\mathrm{PO}_{2}\)). They behave as acids because they can donate H+ ions to a base. On the other hand, NaOH and KOH are bases because they generate hydroxide ions (OH-) that can accept H+ ions from an acid.