AP Chemistry Flashcards: pH and pKa
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What determines the protonation state, and therefore the properties (like color), of an acid-base indicator?
The protonation state of an acid-base indicator is determined by the pH of the solution it is in.
Card 1 of 10
All Flashcards (10)
What determines the protonation state, and therefore the properties (like color), of an acid-base indicator?
The protonation state of an acid-base indicator is determined by the pH of the solution it is in.
How can you predict the predominant form of a weak acid in a solution?
The predominant form (acid or conjugate base) can be predicted by comparing the solution's pH to the acid's pKa.
Summarize the relationship between pH, pKa, and the relative concentrations of a weak acid (HA) and its conjugate base (A⁻).
The relative concentrations of HA and A⁻ depend on the solution pH compared to the acid's pKa; this comparison determines the protonation state.
How should an acid-base indicator be selected to ensure accurate titration results?
The indicator should be selected to have a pKa that is close to the pH at the equivalence point of the titration.
What is the predominant species of a weak acid when the solution pH is greater than the acid's pKa?
If the pH is greater than the pKa (pH > pKa), the deprotonated conjugate base form (A−) dominates the solution.
A solution containing a weak acid with a pKa of 8.1 is adjusted to a pH of 10.0. Which species will be in higher concentration, the acid or its conjugate base?
Because the pH (10.0) is greater than the pKa (8.1), the conjugate base form (A⁻) will be in higher concentration.
A weak acid has a pKa of 4.7. In a solution with a pH of 2.5, which form is predominant: the acid (HA) or the base (A⁻)?
Since the pH (2.5) is less than the pKa (4.7), the acid form (HA) will be the predominant species.
What is an acid-base indicator?
An acid-base indicator is a substance that changes its properties, like color, depending on its protonation state, which is determined by the solution pH.
The equivalence point of a titration is expected to be at pH 9.0. Which indicator is a better choice: one with pKa = 7.0 or one with pKa = 8.9?
The indicator with a pKa of 8.9 is the better choice because its pKa is very close to the pH at the equivalence point.
What is the predominant species of a weak acid when the solution pH is less than the acid's pKa?
If the pH is less than the pKa (pH < pKa), the protonated acid form (HA) dominates the solution.