Aunque en el apéndice D aparece la constante de disociación...

Aunque en el apéndice $D$ aparece la constante de disociación ácida del fenol $\left(\mathrm{C}_6 \mathrm{H}_5 \mathrm{OH}\right)$, no se incluye la constante de disociación básica del ion fenolato $\left(\mathrm{C}_6 \mathrm{H}_5 \mathrm{O}^{-}\right)$. (a) Explique por qué no es necesario incluir tanto la $K_a$ del fenol como la $K_b$ del ion fenolato. (b) Calcule la $K_b$ del ion fenolato. (c) Es el ion fenolato una base más fuerte o más débil que el amoniaco?

Key Concepts

Relationship between Ka, Kb, and Kw

In aqueous solutions, the acid dissociation constant (Ka) of an acid and the base dissociation constant (Kb) of its conjugate base are connected through the autoionization constant of water (Kw), such that Ka × Kb = Kw. This relationship allows for the computation of one constant when the other is known, facilitating the study of acid-base phenomena without redundant data.

Acid-Base Equilibrium

This concept refers to the reversible process in which acids donate protons and bases accept them in aqueous solution. In acid-base equilibria, the extent to which an acid dissociates is quantified by its acid dissociation constant (Ka), and for bases, by the base dissociation constant (Kb). Understanding this equilibrium is crucial when analyzing the behavior of conjugate acid-base pairs.

Conjugate Acid-Base Pairs

A conjugate acid-base pair is formed when an acid donates a proton to become its conjugate base or when a base accepts a proton to form its conjugate acid. The strengths of acids and bases in these pairs are inversely related, meaning that a weak acid will have a relatively strong conjugate base and vice versa. This interplay is key to understanding why it is unnecessary to list both the Ka of an acid and the Kb of its conjugate base independently.

Relative Strengths of Bases

Determining whether one base is stronger or weaker than another involves comparing their base dissociation constants (Kb). A larger Kb indicates a stronger base that more readily accepts protons, while a smaller Kb indicates a weaker base. This comparison is essential for predicting reaction directions and understanding the behavior of different bases under similar conditions.

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