Question

The correct statement(s) about the oxoacids, \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\), is(are) [A] The central atom in both \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\) is \(s p^{3}\) hybridized [B] \(\mathrm{HClO}_{4}\) is more acidic than \(\mathrm{HClO}\) because of the resonance stabilization of its anion [C] \(\mathrm{HClO}_{4}\) is formed in the reaction between \(\mathrm{Cl}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) [D] The conjugate base of \(\mathrm{HClO}_{4}\) is weaker base than \(\mathrm{H}_{2} \mathrm{O}\)

Short answer

[A] and [B] are correct. The central atom in both \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\) is \(sp^3\) hybridized. \(\mathrm{HClO}_{4}\) is more acidic than \(\mathrm{HClO}\) because the conjugate base \(\mathrm{ClO}_{4}^{-}\) is stabilized by resonance, making it less likely to re-accept a proton.

Step-by-step solution

Analyzing the Central Atom Hybridization

The hybridization of the central atom, chlorine, in both \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\) can be determined by looking at the number of atoms bonded to chlorine and the number of lone pairs on chlorine. In \(\mathrm{HClO}_{4}\), chlorine is bonded to four oxygen atoms with no lone pairs, suggesting \(sp^3\) hybridization. In \(\mathrm{HClO}\), chlorine is bonded to one oxygen atom and has three lone pairs, also suggesting \(sp^3\) hybridization.

Comparing Acid Strength

The acid strength can be compared by looking at the stability of the conjugate base. \(\mathrm{HClO}_{4}\) is a stronger acid than \(\mathrm{HClO}\) because the anion \(\mathrm{ClO}_{4}^{-}\) is highly stable due to delocalization of charges (resonance stabilization), whereas \(\mathrm{ClO}^{-}\) has less resonance stabilization.

Examining Reaction Formation

To determine if statement [C] is correct, consider the chemical reaction between \(\mathrm{Cl}_{2}\) and \(\mathrm{H}_{2}O\). This reaction usually forms a mixture of acids including hydrochloric acid (HCl) and hypochlorous acid (HClO), not \(\mathrm{HClO}_{4}\), which is typically prepared through other processes involving oxidizers.

Assessing the Conjugate Base Strength

The conjugate base of \(\mathrm{HClO}_{4}\) is \(\mathrm{ClO}_{4}^{-}\) which is a very weak base due to its resonance stabilization and delocalization of charge. Water (\(\mathrm{H}_{2}O\)) is a much stronger base compared to \(\mathrm{ClO}_{4}^{-}\). Hence, the conjugate base of \(\mathrm{HClO}_{4}\) is indeed a weaker base than \(\mathrm{H}_{2}O\).

Key concepts

Acid Strength Comparison

Understanding the relative strengths of oxoacids, such as \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\), involves exploring how the structure of the molecule affects its ability to donate a proton. In comparing the two, we observe that \(\mathrm{HClO}_{4}\) is significantly more acidic than \(\mathrm{HClO}\).

This difference is largely due to the stability of their conjugate bases; a more stable conjugate base means the original acid was stronger. The conjugate base of \(\mathrm{HClO}_{4}\), which is \(\mathrm{ClO}_{4}^{-}\), exhibits a remarkable stability owing to the resonance stabilization, where the negative charge can be delocalized over the four oxygen atoms.

In contrast, \(\mathrm{ClO}^{-}\), the conjugate base of \(\mathrm{HClO}\), has limited opportunities for resonance stabilization with only one oxygen atom available, making it less stable and hence, \(\mathrm{HClO}\) a weaker acid. The implication for students is clear: the more resonance an anion can engage in, the more stable it is, and the stronger its parent acid will be.

Central Atom Hybridization

When discussing oxoacids such as \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\), the hybridization of the central atom chlorine is a critical aspect of their molecular structures. Both \(\mathrm{HClO}_{4}\) and \(\mathrm{HClO}\) have chlorine atoms that are \(sp^3\) hybridized.

Understanding hybridization helps us to visualize the spatial arrangement of atoms and the potential for overlap in atomic orbitals. In \(\mathrm{HClO}_{4}\), chlorine has four single bonds to oxygen atoms, fitting the \(sp^3\) hybridization, which indicates one s orbital and three p orbitals are mixed to form four equivalent \(sp^3\) orbitals. The same applies to \(\mathrm{HClO}\) where the chlorine atom has one single bond to oxygen and three lone pairs, which also necessitates \(sp^3\) hybridization.

This underlying structure plays a role in the stability and reactivity of the molecule. For students, recognizing hybridization patterns is essential in predicting how atoms connect in complex molecules.

Conjugate Base Stability

A critical factor influencing the acidity of a molecule is the stability of its conjugate base. A stronger acid will have a more stable conjugate base post-proton donation, and this stability is often gauged by the delocalization of the negative charge.

The stability of \(\mathrm{ClO}_{4}^{-}\), the conjugate base of the strong acid \(\mathrm{HClO}_{4}\), arises from its ability to delocalize the negative charge through resonance across multiple oxygen atoms. This distribution reduces electron density on any single atom, thereby lowering repulsion and contributing to stability.

With \(\mathrm{HClO}\), its weaker acidity is linked to the conjugate base \(\mathrm{ClO}^{-}\), which lacks the extensive resonance stabilization of \(\mathrm{ClO}_{4}^{-}\) and thereby is less stable. By delving into the concept of resonance and charge delocalization, students gain insight into why some ions are more stable than others, influencing the acid-base properties of their corresponding acids.