Problem 146 - A Complete Resource Book in Chemistry for JEE Main

Question

The increasing order of the oxidizing capacity of the oxyacids of chlorine is (a) \(\mathrm{HClO}_{4}<\mathrm{HClO}_{3}<\mathrm{HClO}_{2}<\mathrm{HClO}\) (b) \(\mathrm{HClO}_{3}<\mathrm{HClO}_{4}<\mathrm{HClO}_{2}<\mathrm{HClO}\) (c) \(\mathrm{HClO}_{4}<\mathrm{HClO}_{3}<\mathrm{HClO}<\mathrm{HClO}_{2}\) (d) \(\mathrm{HClO}^{4}<\mathrm{HClO}_{2}^{3}<\mathrm{HClO}_{3}<\mathrm{HClO}_{4}^{2}\)

Step-by-Step Solution

Answer

The correct order is option (a): \( \mathrm{HClO}_{4}<\mathrm{HClO}_{3}<\mathrm{HClO}_{2}<\mathrm{HClO} \).

Step 1: Understanding Oxidizing Capacity

The oxidizing capacity of a compound is its ability to accept electrons, which often correlates inversely with the stability of the compound's oxidation state. Oxyacids of chlorine have chlorine in different oxidation states and their oxidizing power generally increases as the number of oxygen atoms attached to chlorine decreases.

Step 2: Identifying Oxidation States of Each Acid

For each of the given oxyacids, let's determine the oxidation state of chlorine: 1. In \( \mathrm{HClO} \), chlorine has an oxidation state of +1.2. In \( \mathrm{HClO}_{2} \), chlorine's oxidation state is +3.3. In \( \mathrm{HClO}_{3} \), it's +5.4. In \( \mathrm{HClO}_{4} \), chlorine's oxidation state is +7.

Step 3: Ranking Based on Oxidation States

The general rule is the higher the oxidation state of chlorine in an oxyacid, the weaker its oxidizing power because it is more stable and less likely to gain electrons. Thus, the oxidizing capacity decreases from \( \mathrm{HClO} \) to \( \mathrm{HClO}_{4} \).

Step 4: Arrange in Increasing Order of Oxidizing Power

Arranging these acids in ascending order of their oxidizing power corresponds to descending order of their oxidation states of chlorine: - \( \mathrm{HClO}_{4} \)- \( \mathrm{HClO}_{3} \)- \( \mathrm{HClO}_{2} \)- \( \mathrm{HClO} \)

Step 5: Matching with Given Options

Now, compare our arrangement with the given options. The order of increasing oxidizing power matches option (a): \[ \mathrm{HClO}_{4}<\mathrm{HClO}_{3}<\mathrm{HClO}_{2}<\mathrm{HClO} \]

Key Concepts

Oxidation States

In chemistry, oxidation states help us understand how atoms in a molecule share their electrons. For chlorine in its oxyacids, the oxidation state varies depending on how many oxygen atoms are bonded to it. Each oxygen atom typically takes away some electron share from chlorine, raising its oxidation state.
For example, in hypochlorous acid (\( \mathrm{HClO} \)), chlorine has an oxidation state of +1 because there is only one oxygen pulling electrons away. As the number of oxygens increases, as seen in chlorous acid (\( \mathrm{HClO}_{2} \)), chloric acid (\( \mathrm{HClO}_{3} \)), and perchloric acid (\( \mathrm{HClO}_{4} \)), the oxidation states rise to +3, +5, and +7, respectively.

• Hypochlorous Acid: +1
• Chlorous Acid: +3
• Chloric Acid: +5
• Perchloric Acid: +7

Knowing these oxidation states helps predict behavior in chemical reactions, as higher states generally mean more electron loss initially.

Oxidizing Power

Oxidizing power refers to the ability of a substance to accept electrons during a chemical reaction. Oxyacids of chlorine showcase a range of oxidizing powers which are deeply connected to their oxidation states.
Typically, the lower the oxidation state, the stronger the oxidizing agent. This is because compounds with chlorine at lower oxidation states can more readily accept electrons. For instance, \( \mathrm{HClO} \) is a strong oxidizer due to chlorine being more eager to gain electrons back, having an oxidation state of +1. As you follow the series to \( \mathrm{HClO}_{4} \), with chlorine in a stable +7 state, its urgency to gain more electrons diminishes, making it a weaker oxidizing agent.

• More oxygen atoms mean a higher oxidation state and a weaker oxidizing power.
• Higher oxidation states lead to greater stability and reduced electron acceptance.

Thus, the flow of oxidizing power from \( \mathrm{HClO} \) to \( \mathrm{HClO}_{4} \) represents decreasing oxidizing strength.

Chlorine Chemistry

Chlorine, known for its vibrant chemistry, can display diverse oxidation states, making it a versatile element in chemical reactions. Its oxyacids are a prime example of its capacity to engage in redox reactions.
In \( \mathrm{HClO} \), for instance, chlorine's lower oxidation state allows it to function as a potent disinfectant. It rapidly accepts electrons, effectively oxideing other components—the essence of its powerful oxidizing capability.
As we progress to hydroxy acids such as \( \mathrm{HClO}_{2} \), \( \mathrm{HClO}_{3} \), and \( \mathrm{HClO}_{4} \), chlorine engages differently. In higher oxidation states like in \( \mathrm{HClO}_{4} \), chlorine becomes part of a more stable and less reactive formation. Thus, each oxyacid finds unique applications based on its chemical characteristics:
- \( \mathrm{HClO} \) for disinfection- \( \mathrm{HClO}_{2} \), \( \mathrm{HClO}_{3} \), and \( \mathrm{HClO}_{4} \) in industrial and laboratory oxidizing reactionsUnderstanding chlorine chemistry, including the behavior of its oxyacids, equips students and scientists to harness these substances effectively in practical applications.