Is the conjugate base of a weak acid a strong base? Explain. Explain why \(\mathrm{Cl}^{-}\) does not affect the pH of an aqueous solution.

Strong acids and bases are compounds that completely dissociate into their ions in water. In contrast, weak acids and bases only partially dissociate in water, resulting in an equilibrium between the acid/base and its ions. The strength of an acid or base is determined by its ability to donate or accept protons (H⁺ ions).

Whenever an acid donates a proton, the remaining part of the molecule acts as the conjugate base. Similarly, when a base accepts a proton, it forms a conjugate acid. The conjugate acid/base pair represents the two species that differ only by the presence or absence of a specific H⁺ ion.

The strength of an acid and its conjugate base are inversely related. This means that if an acid is strong, its conjugate base will be weak and vice versa. However, it is essential to note that a weak acid's conjugate base does not necessarily mean it is a strong base; it can be weaker or still a weak base. Now, let's answer the first part of the exercise: Is the conjugate base of a weak acid a strong base? No, the conjugate base of a weak acid is not necessarily always a strong base. Often, the conjugate base of a weak acid is also weak. The reason is that a weak acid does not dissociate completely in water, so its conjugate base will also not dissociate entirely, making it unable to accept protons efficiently. Thus, the conjugate base of a weak acid can also be weak or less efficient at accepting protons than a strong base. For the second part of the exercise, we need to explain why Cl⁻ does not affect the pH of an aqueous solution:

The chloride ion (Cl⁻) is the conjugate base of hydrochloric acid (HCl), which is a strong acid. When HCl dissociates in water, it donates its H⁺ ion to H₂O and forms Cl⁻ and hydronium (H₃O⁺): \[HCl (aq) + H_2O (l) \rightarrow Cl^{-} (aq) + H_{3}O^{+}(aq) \] Since HCl is a strong acid, it donates its proton completely, making the resulting chloride ion (Cl⁻) weak or even considered "inactive" as a base. In aqueous solutions, the Cl⁻ ion does not readily react with water or accept H⁺ ions from other molecules. Consequently, Cl⁻ ions do not affect the pH of an aqueous solution, as they don't contribute to the concentration of hydronium ions (H₃O⁺) or hydroxide ions (OH⁻).