Chemistry

Chemistry

Problem

Which of the following mathematical expressions correctly relates the pH of a buffer solution to the acid dissociation constant (KaK_a) of the weak acid and the ratio of the concentrations of its conjugate base (A−A^-) to the acid (HAHA)? a) pH=pKa+[A−][HA]\text{pH} = \text{p}K_a + \dfrac{[A^-]}{[HA]} b) pH=Ka+log⁡([A−][HA])\text{pH} = K_a + \log\left(\dfrac{[A^-]}{[HA]}\right) c) pH=pKa+log⁡([A−][HA])\text{pH} = pK_a + \log\left(\dfrac{[A^-]}{[HA]}\right) d) pH=pKa+log⁡([HA][A−])\text{pH} = pK_a + \log\left(\dfrac{[HA]}{[A^-]}\right)
Intuitive explanation

The Henderson-Hasselbalch equation is the key relationship that connects pH to KaK_a and the ratio of conjugate base to weak acid. Rather than deriving it from scratch each time, you can remember that pH depends logarithmically on this ratio—when you have more conjugate base relative to acid, the pH increases, and vice versa. The equation elegantly captures how a buffer resists pH change by balancing the weak acid and its conjugate base.

Intuitive explanation

The Henderson-Hasselbalch equation is the key relationship that connects pH to KaK_a and the ratio of conjugate base to weak acid. Rather than deriving it from scratch each time, you can remember that pH depends logarithmically on this ratio—when you have more conjugate base relative to acid, the pH increases, and vice versa. The equation elegantly captures how a buffer resists pH change by balancing the weak acid and its conjugate base.

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