Problem 65 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is the strongest acid? (a) \(\mathrm{ClO}_{3}(\mathrm{OH})\) (b) \(\mathrm{ClO}_{2}(\mathrm{OH})\) (c) \(\mathrm{SO}(\mathrm{OH})_{2}\) (d) \(\mathrm{SO}_{2}(\mathrm{OH})_{2}\)

Step-by-Step Solution

Answer

The strongest acid is \( \mathrm{ClO}_{3}(\mathrm{OH}) \).

Step 1: Calculate the Negative Oxidation States

Determine the oxidation number of chlorine and sulfur in each compound to identify the oxidation states. Higher oxidation states generally correspond to stronger acids. For \( \mathrm{ClO}_{3}(\mathrm{OH}) \), chlorine has an oxidation state of +7. For \( \mathrm{ClO}_{2}(\mathrm{OH}) \), chlorine has an oxidation state of +5. For \( \mathrm{SO}(\mathrm{OH})_{2} \), sulfur’s oxidation state is +4. For \( \mathrm{SO}_{2}(\mathrm{OH})_{2} \), sulfur’s oxidation state is +6.

Step 2: Compare Oxidation States for Acidity

Compare each compound’s oxidation number, noting that stronger acids generally exhibit a higher oxidation state. - \( \mathrm{ClO}_{3}(\mathrm{OH}) \) with chlorine at +7- \( \mathrm{SO}_{2}(\mathrm{OH})_{2} \) with sulfur at +6These have higher oxidation states compared to the other two compounds, indicating they are stronger acids.

Step 3: Final Comparison Based on Known Acid Strengths

Compare briefly known acid strengths for chloric and sulfuric acids. Chloric acid (\( \mathrm{ClO}_{3}(\mathrm{OH}) \)) is a known strong acid. Sulfuric acid (\( \mathrm{SO}_{2}(\mathrm{OH})_{2} \)) is also a very strong acid, but generally, chloric acid (due to its high oxidation state and known strength) is stronger.

Key Concepts

Oxidation State

The oxidation state of an element in a compound indicates how many electrons an atom has gained, lost, or shared when forming a chemical bond. In essence, it helps us to understand the degree of oxidation of an atom.

When determining acid strength, the oxidation state can be a key factor. Usually, the higher the oxidation state, the stronger the acid becomes. This rule is particularly helpful when comparing oxyacids, which are acids that contain oxygen.

• For example, in chloric acid (\( \text{ClO}_3(\text{OH}) \)), chlorine possesses an oxidation state of +7.
• In contrast, sulfur has a lower oxidation state of +4 in sulfurous acid (\(\text{SO}(\text{OH})_2\)).

Therefore, when evaluating acid strength, the higher oxidation state of chlorine in chloric acid hints at its strong acidic nature compared to sulfurous acid.

Chloric Acid

Chloric acid, expressed as \(\text{ClO}_3(\text{OH})\), represents a potent oxyacid of chlorine. One significant feature of chloric acid is its high oxidation state of +7 for chlorine, which contributes greatly to its strong acidity.

Chloric acid dissociates completely in water, demonstrating its strong acidic properties. The substantial oxidation state of chlorine signifies that the proton (H\(^+\)) can be easily released in solution, which is a hallmark of strong acids.

• This complete ionization in water classifies chloric acid as a strong acid.
• Its robustness as an acid makes it a point of interest in various chemical reactions.

However, it is less commonly encountered in the laboratory due to its instability. This reinforces the importance of understanding its theoretical behavior rather than its practical handling.

Sulfuric Acid

Sulfuric acid, known chemically as \(\text{SO}_2(\text{OH})_2\), is one of the most industrially significant strong acids. In sulfuric acid, sulfur has an oxidation state of +6, which effectively contributes to its powerful acidic nature.

This acid is characterized by its ability to release two protons, as it is a dibasic acid. Its dissociation primarily involves the release of one proton, with the second one dissociating somewhat more weakly.

• Sulfuric acid fully dissociates its first hydrogen ion when dissolved in water, marking it as a strong acid for this first ionization.
• The second ionization, while less complete, still adds to its overall acidity.

Due to its high reactivity and effectiveness as an oxidizing agent, sulfuric acid finds applications in a vast array of chemical processes. Understanding sulfur's oxidation state helps comprehend its potent acidic and reactive properties.