Problem 32 - A Complete Resource Book in Chemistry for JEE Main

Question

Of the given anions, the strongest bronsted base is (a) \(\mathrm{ClO}_{4}^{-}\) (b) \(\mathrm{ClO}_{3}^{-}\) (c) \(\mathrm{ClO}_{2}^{-}\) (d) \(\mathrm{ClO}^{-}\)

Step-by-Step Solution

Answer

The strongest Bronsted base is \( \mathrm{ClO}^{-} \).

Step 1: Understanding Bronsted Bases

A Bronsted base is a species that can accept a proton (H⁺). To determine the strength of a Bronsted base, we often consider the stability of the conjugate acid formed when the base accepts a proton.

Step 2: Analyze Conjugate Acids

For each anion, the conjugate acid is formed by adding H⁺. So, the conjugate acids are: - For \(\mathrm{ClO}_{4}^{-}\), the conjugate acid is \(\mathrm{HClO}_{4}\)- For \(\mathrm{ClO}_{3}^{-}\), the conjugate acid is \(\mathrm{HClO}_{3}\)- For \(\mathrm{ClO}_{2}^{-}\), the conjugate acid is \(\mathrm{HClO}_{2}\)- For \(\mathrm{ClO}^{-}\), the conjugate acid is \(\mathrm{HClO}\)

Step 3: Consider Acid Strength

The stronger the conjugate acid, the weaker the base. We need to consider the acid strengths: - \(\mathrm{HClO}_{4}\) is a very strong acid- \(\mathrm{HClO}_{3}\) is also a strong acid- \(\mathrm{HClO}_{2}\) is a weak acid- \(\mathrm{HClO}\) is a very weak acid

Step 4: Determine the Strongest Base

Since \(\mathrm{HClO}\) is the weakest acid among the conjugate acids, its corresponding base \(\mathrm{ClO}^{-}\) is the strongest base. The strength of the base is inversely related to the strength of the conjugate acid.

Key Concepts

Conjugate Acid

In the world of acids and bases, understanding conjugate acids is pivotal. When a base accepts a proton, it transforms into its conjugate acid. This process helps us understand the behavior of substances in reactions. For example, when an anion such as \( \mathrm{ClO}^{-} \) accepts a proton (H⁺), it becomes \( \mathrm{HClO} \), which is its conjugate acid. This principle applies to other anions as well, such as \( \mathrm{ClO}_{2}^{-} \), \( \mathrm{ClO}_{3}^{-} \), and \( \mathrm{ClO}_{4}^{-} \), each forming their respective conjugate acids. The transformation from base to conjugate acid is crucial for predicting how anions will behave when they encounter protons.

Acid Strength

The strength of an acid is a measure of its ability to donate a proton. Understanding this concept is key in predicting the behavior of its conjugate base. In our example, when comparing the acids \( \mathrm{HClO} \), \( \mathrm{HClO}_{2} \), \( \mathrm{HClO}_{3} \), and \( \mathrm{HClO}_{4} \), we find a range of acid strengths:

• \( \mathrm{HClO}_{4} \) is a very strong acid.
• \( \mathrm{HClO}_{3} \) is also strong, but slightly less than \( \mathrm{HClO}_{4} \).
• \( \mathrm{HClO}_{2} \) is weaker.
• \( \mathrm{HClO} \) is the weakest among these acids.

The stronger the acid, the weaker its conjugate base will be. This is because strong acids easily donate protons, leaving behind a less reactive conjugate base.

Anion Stability

An important aspect to consider in the behavior of Bronsted bases is the stability of their anions. Stability can be thought of as how comfortable an anion feels by itself without gaining a proton. Typically, the less stable the anion, the more likely it is to react with a proton to form a stable compound. For instance, \( \mathrm{ClO}^{-} \) is less stable compared to its counterparts like \( \mathrm{ClO}_{4}^{-} \). This instability makes \( \mathrm{ClO}^{-} \) more eager to accept a proton, thereby acting as a stronger base. It is crucial to analyze this characteristic when predicting reaction behavior, as more stable anions will prefer to stay as they are, reflecting their weak base nature.

Proton Acceptance

At the heart of Bronsted base behavior is the concept of proton acceptance. A Bronsted base is defined by its ability to accept protons. The ease with which this occurs is influenced by the structure and energy state of the anion. In the case of \( \mathrm{ClO}^{-} \), its high proton acceptance ability is linked to the weak nature of its conjugate acid \( \mathrm{HClO} \). Since \( \mathrm{HClO} \) is a weak acid, its conjugate base, \( \mathrm{ClO}^{-} \), strongly attracts protons. Thus, knowing how easily an anion can integrate an additional proton highlights its base strength and potential reactivity.