Phenol, C6 H5 OH, has a Ka of 1.3 ×10^-10 (a) Write out the Ka reaction for phenol. (b) Calculat

step 1 Option A, phenol undergoes a partial dissociation in water. So let me represent it by reaction.

Phenol, C6 H5 OH, has a Ka of 1.3 ×10^-10 (a) Write out the...

Phenol, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH},$ has a $K_{a}$ of $1.3 \times 10^{-10}$
(a) Write out the $K_{a}$ reaction for phenol.
(b) Calculate $K_{b}$ for phenol's conjugate base.
(c) Is phenol a stronger or weaker acid than water?

Key Concepts

Acid Dissociation Constant (Ka)

This constant measures the extent to which an acid dissociates in water into its ions. It quantifies the equilibrium between the undissociated acid and the products (typically, a proton and its conjugate base) in an aqueous solution. A higher Ka value indicates a stronger acid, as the equilibrium favors the formation of ions.

Base Dissociation Constant (Kb)

Kb is analogous to Ka but for bases. It expresses the extent to which a base reacts with water to produce its conjugate acid and hydroxide ions. For a conjugate base of a weak acid, Kb can be calculated using the relationship with Kw (the ionization constant of water) and Ka, namely Kb = Kw/Ka.

Conjugate Acid-Base Pairs

A conjugate acid-base pair consists of two species that differ by one proton. When an acid donates a proton, it forms its conjugate base, which in turn can accept a proton to recreate the acid. The strength of an acid is inversely related to the strength of its conjugate base according to the relationship between Ka and Kb.

Water Ionization Constant (Kw)

Kw represents the equilibrium constant for the self-ionization of water into hydrogen ions and hydroxide ions. At a given temperature (usually 25°C), it has a fixed value, enabling a quantitative relationship between the acid dissociation constant (Ka) and the base dissociation constant (Kb) for conjugate acid-base pairs, as expressed by the equation Ka × Kb = Kw.

Acid Strength Comparison

Acid strength is often compared by looking at their respective Ka values. An acid with a larger Ka dissociates more completely in water, making it a stronger acid. Additionally, the relative strengths can be compared using the corresponding conjugate base strengths via their Kb values, where a smaller Kb for the conjugate base implies a stronger parent acid.

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