Multiple Choice
Consider a 1.0 M solution of a hypothetical weak acid HA whose pKa is 11. Calculate the pH of this solution.
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17. Acid and Base Equilibrium
pH of Weak Acids
Multiple Choice
At the equivalence point during the titration of a weak acid with a strong base, would the pH be acidic, neutral, or basic?
A
Basic
B
Acidic
C
Neutral
Verified step by step guidance1
Understand what happens at the equivalence point in a titration: it is the point where the amount of strong base added exactly neutralizes the weak acid present.
Recognize that the weak acid (HA) reacts with the strong base (OH⁻) to form its conjugate base (A⁻) and water, according to the reaction: \(\mathrm{HA + OH^- \rightarrow A^- + H_2O}\).
At the equivalence point, all the weak acid has been converted to its conjugate base (A⁻), which remains in solution.
Since the conjugate base (A⁻) is the conjugate of a weak acid, it can hydrolyze with water to produce OH⁻ ions, increasing the pH: \(\mathrm{A^- + H_2O \rightleftharpoons HA + OH^-}\).
Therefore, the solution at the equivalence point is basic because of the presence of the conjugate base that raises the pH above 7.
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