Based on their compositions and structures and on conjugate...

Based on their compositions and structures and on conjugate acid-base relationships, select the stronger base in each of the following pairs: (a) $\mathrm{BrO}^{-}$ or $\mathrm{ClO}^{-},(\mathbf{b}) \mathrm{BrO}^{-}$ or $\mathrm{BrO}_{2}^{-}$, (c) $\mathrm{HPO}_{4}^{2-}$ or $\mathrm{H}_{2} \mathrm{PO}_{4}^{-}$.

Key Concepts

Acid Strength in Polyprotic Systems

In polyprotic acid systems, successive deprotonations result in conjugate bases that exhibit different basic strengths. The degree of protonation affects the charge distribution and stability of the anion; typically, the deprotonated form with the higher negative charge is the stronger base, provided that additional stabilization (resonance, inductive effects) does not overly delocalize the charge.

Inductive Effects of Electronegative Atoms

Oxygen atoms, being highly electronegative, withdraw electron density through the sigma bonds (inductive effect). This electron-withdrawing effect reduces the electron density of the base, making it less likely to donate electrons or accept a proton, and consequently weakening its basicity. This effect is pronounced in comparing species with different numbers of oxygen atoms.

Resonance Stabilization

Resonance stabilization describes how a negative charge can be spread over several atoms through multiple resonance structures. When the charge is delocalized, the species becomes more stable and less eager to react with a proton, thereby reducing its basicity. This concept is influential when evaluating the basicity of species that differ in the number of oxygen atoms attached to the central atom.

Conjugate Acid?Base Relationships

This concept involves the understanding that every acid has a conjugate base and vice versa. The strength of a base is inversely related to the strength of its conjugate acid; a weak acid has a strong conjugate base, while a strong acid has a weak conjugate base. This principle is crucial when comparing species based on the acidity of their corresponding conjugate acids.

Electronegativity and Atomic Size

Electronegativity and atomic size fundamentally influence basicity. For instance, when comparing analogous anions, the central atom’s electronegativity affects charge distribution; a less electronegative atom typically holds the negative charge less tightly, which can increase basicity. Atomic size also plays a role, as larger atoms can better accommodate and delocalize negative charge.

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