Multiple Choice
What is the H₃O⁺ concentration of a 0.250 M hydrofluoric acid (HF) solution, given that the acid dissociation constant (Ka) for HF is 6.8 x 10⁻⁴?
17. Acid and Base Equilibrium
pH of Weak Acids
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Which formula can be used to calculate the pH of a weak acid given its pKa and concentration?
A
pH = pKa - log([A-]/[HA])
B
pH = -log([H+])
C
pH = pKa + log([HA]/[A-])
D
pH = pKa + log([A-]/[HA])
Verified step by step guidance1
Identify the relationship between pH, pKa, and the concentrations of the acid and its conjugate base. This is described by the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation is used to calculate the pH of a buffer solution, which consists of a weak acid and its conjugate base.
The equation is given by: , where [A^-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid.
In the context of the problem, the correct formula to calculate the pH of a weak acid given its pKa and concentration is the Henderson-Hasselbalch equation.
Therefore, the correct answer is: .
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