Problem 87 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

increasing acid strength : \(\mathrm{HClO}_{3}, \mathrm{HClO}_{4}, \mathrm{HClO}_{2}, \mathrm{HClO}\)

Step-by-Step Solution

Answer

Increasing order: \(\mathrm{HClO}\), \(\mathrm{HClO}_{2}\), \(\mathrm{HClO}_{3}\), \(\mathrm{HClO}_{4}\).

Step 1: Understand Acid Strength

The strength of an oxoacid is determined by the number of oxygen atoms attached to the central atom. More oxygen atoms typically result in stronger acids due to increased pull on the electron density, which stabilizes the negative charge after dissociation.

Step 2: Analyze Each Acid's Structure

Examine each acid: - \(\mathrm{HClO}\): 1 oxygen atom- \(\mathrm{HClO}_{2}\): 2 oxygen atoms- \(\mathrm{HClO}_{3}\): 3 oxygen atoms- \(\mathrm{HClO}_{4}\): 4 oxygen atomsGiven the number of oxygen atoms, a higher number indicates a stronger acid.

Step 3: Rank the Acids Based on Oxygen Atoms

Place the acids in order of their increasing number of oxygen atoms, which reflects their increasing acid strength: - \(\mathrm{HClO}\) < \(\mathrm{HClO}_{2}\) < \(\mathrm{HClO}_{3}\) < \(\mathrm{HClO}_{4}\).

Step 4: Verify Order with Acid Strength

Confirm that \(\mathrm{HClO}_{4}\) is the strongest acid, because it has the most oxygen atoms, making it easiest to lose a proton. \(\mathrm{HClO}\) should be the weakest.

Key Concepts

Oxoacids

Oxoacids are a fascinating group of compounds in chemistry. These acids are typically made up of at least one hydrogen atom bonded to an oxygen atom. Moreover, this oxygen atom bonds to another element. The element is often very electronegative, such as chlorine in the case of compounds like - HClO - HClO2 - HClO3 - HClO4.
The structure and number of these oxygen atoms play a crucial role in determining the strength of the oxoacid. A central atom, which is not oxygen or hydrogen, can vary, influencing the properties of these acids. However, in common oxoacids like those of chlorine, the central element remains constant. This means we can focus more on the varying number of oxygen atoms connected to this central chlorine atom to understand their strength. The more oxygen around the central atom, the stronger the oxoacid generally becomes.

Oxygen Atom Influence on Acidity

The number of oxygen atoms in an oxoacid has a notable effect on its acidity. More oxygen atoms enhance the acid's ability to dissociate hydrogen ions. Here's how it works:
Oxygen is highly electronegative. This means it pulls electron density towards itself more than many other atoms do. When more oxygen atoms are attached to the central atom, there is a stronger electron-withdrawing effect. - This effect increases the stability of the conjugate base after dissociation. - Consequently, it facilitates the release of a proton (H⁺) into the solution.
This is why - HClO4, with four oxygen atoms, is a stronger acid compared to HClO, which has only one oxygen atom. The additional oxygen atoms not only increase the acidity but also contribute to making the resulting anion more stable through resonance effects. Each additional oxygen provides more centers to delocalize the negative charge, strengthening the acid's ability to lose a proton.

Acid Dissociation

Acid dissociation involves the process where an acid releases a proton into a solution. This is a central concept when discussing acid strength, especially in oxoacids. When an oxoacid dissociates, it releases an H⁺ ion, leaving behind a conjugate base. The efficiency and ease with which an acid dissociates link directly to its strength.

• A strong acid dissociates completely in solution, readily giving up its proton.
• A weak acid only partially dissociates, keeping a portion of its hydrogen ions bound.

For oxoacids, such as those listed earlier: - HClO4 dissociates more completely than HClO, in part because the stable anion that remains is well-supported by multiple oxygen atoms. The stability of this conjugate base post-dissociation is crucial, as it determines how easily the acid can "let go" of its proton. The better an acid can dissociate and stabilize the resulting charges, the stronger that acid is considered to be.