Question

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

Short answer

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

Step-by-step solution

Understanding the Problem

We need to identify the strongest Brønsted base among the given anions: \( \mathrm{ClO}_{4}^{-} \), \( \mathrm{ClO}_{3}^{-} \), \( \mathrm{ClO}_{2}^{-} \), and \( \mathrm{ClO}^{-} \). A Brønsted base is a species that accepts a proton.

Identify Feature Affecting Basicity

The ability of an anion to act as a base and accept a proton depends on its stability and the availability of negative charge to bind with \( H^+ \). Typically, less stable anions (or those with more negative charge density) are stronger bases.

Stability and Electronegativity Considerations

Electrons are more delocalized in anions like \( \mathrm{ClO}_{4}^{-} \), which have resonance structures that stabilize the charge. Chlorine is very electronegative and stabilizes the negative charge on the oxyanions as the number of oxygen atoms increases.

Identify Patterns

As the number of oxygen atoms in the perchlorate series increases, the stability of the oxyanion increases while the basicity decreases. Thus, \( \mathrm{ClO}_{4}^{-} \) is most stable and least basic, while \( \mathrm{ClO}^{-} \) is least stable and most basic due to less delocalization of charge.

Determine the Strongest Base

Considering the factors, \( \mathrm{ClO}^{-} \) has the least amount of oxygen atoms and hence less stabilization; therefore, it has the highest basicity. It is the strongest Brønsted base as it most readily accepts a proton.

Key concepts

Anion Stability

Anion stability is a fundamental concept in chemistry when discussing the behavior of ions like the perchlorate series. When discussing perchlorate ions, we focus on how the stability influences their chemical behavior—especially how they interact as bases. An anion's stability is deeply connected to how delocalized or spread out its negative charge is.
The more stabilized the charge, the less eager the anion is to attract more protons (which means lesser basicity).
Stability is often enhanced through resonance, where electrons are distributed over multiple atoms or bonds, allowing the charge to be diffused.
For perchlorates:

• [\(\mathrm{ClO}_{4}^{-}\)] is highly stable because of better delocalization due to more resonance structures.
• More oxygen atoms present implies more resonance possibilities, leading to greater charge stability.
• Stable anions do not need to gain additional protons, making them poor bases.

Understanding the link between anion stability and their basicity helps to explain the trends in basicity within the perchlorate series.

Basicity and Charge Density

Basicity in chemistry refers to the ability of a base to accept a proton. This is significantly influenced by charge density on an anion.
Charge density refers to how concentrated a charge is over a particular area. Higher charge density means a more concentrated negative charge on the atom, making it more likely to attract and bond with protons.
For [\(\mathrm{ClO}^{-}\)], with the least number of oxygen atoms, the negative charge is less dispersed.

• This localizes the negative charge around the oxygen and the chlorine, increasing the anion's ability to act as a base.
• Less resonance leads to higher charge density and stronger basicity.

In short, the less spread the charge, the stronger the anion as a base. Hence, [\(\mathrm{ClO}^{-}\)] acts as a stronger Brønsted base compared to its counterparts in the series.

Resonance Structures

Resonance structures in chemistry are alternative Lewis structures for a molecule or ion that depict the distribution of electrons among the atoms.
In resonance, we show the different ways electrons can be shared and spread across different positions within a molecule.
For the perchlorate series, resonance helps in stabilizing the negative charge:

• More resonance structures equal more distribution of charge over the oxygen atoms.
• [\(\mathrm{ClO}_{4}^{-}\)] has the highest number of resonance structures, making it the most stable.

This spread of electron density means the anion has less need to seek out additional protons, hence quieter on the base activity front.
In contrast, less resonance as seen in [\(\mathrm{ClO}^{-}\)] means a strong, localized negative charge and a greater desire to accept protons, enhancing basicity.

Perchlorate Series

The perchlorate series involves different oxyanions related to perchloric acid with varying numbers of oxygen atoms attached to chlorine. This series demonstrates important chemical principles related to stability and basicity.

• [\(\mathrm{ClO}_{4}^{-}\)] (perchlorate) has the most oxygen and is the most stable but least basic.
• [\(\mathrm{ClO}_{3}^{-}\)] (chlorate) and [\(\mathrm{ClO}_{2}^{-}\)] (chlorite) show decreasing stability and increasing basicity as oxygen atoms decrease.
• [\(\mathrm{ClO}^{-}\)] (hypochlorite) is the least stable with highest basicity.

Understanding this series helps in predicting the behavior of such compounds in reactions. The more stable the anion, the less basic it is. This is a key aspect of understanding why [\(\mathrm{ClO}^{-}\)] ends up as the strongest base among them.