The buffer capacity (β) for a weak acid HA and conjugate base (A-) buffer is defined as the number of moles of strong acid or base needed to change the pH of 1 L of solution by 1 pH unit, where β = 2.

Question

The buffer capacity (β) for a weak acid HA and conjugate base (A-) buffer is defined as the number of moles of strong acid or base needed to change the pH of 1 L of solution by 1 pH unit, where β = 2.303(CA + CB)Ka[H+] / ([H+] + Ka)^2. Under what condition will a buffer best resist a change in pH?

Prashant Kotian · Accepted Answer

Correct answer: C. A buffer resists pH changes best when its buffer capacity (β) is maximum. To find the maximum value of β with respect to [H+], we set dβ / d[H+] = 0. This yields [H+] = Ka, which means pH = pKa. Under this condition, the concentrations of weak acid and conjugate base are equal, and the buffer is most effective.

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