This Additional Higher Level mini-lesson covers Reactivity 3.1: Ka, Kb, pKa and pKb, the pH of weak acids, buffers, and pH titration curves.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
For a weak acid HA ⇌ H⁺ + A⁻:
A larger Ka (smaller pKa) means a stronger weak acid. For a conjugate pair, Ka × Kb = Kw and pKa + pKb = 14.
Because dissociation is small, for a weak acid of concentration C:
This assumes [HA] at equilibrium ≈ initial C and [H⁺] ≈ [A⁻].
A buffer resists pH change on adding small amounts of acid or base. An acidic buffer is a weak acid plus its salt (conjugate base):
Plotting pH against added titrant gives characteristic curves. The steep equivalence point depends on the acid/base strengths. For a weak acid with strong base, the half-equivalence point gives pH = pKa. Indicators are chosen so their range spans the steep part.
Tap a description, then the category.
Tap an item on the left, then its match on the right.
Ka & pKa: Ka = [H⁺][A⁻]/[HA]; pKa = −log Ka; smaller pKa = stronger
Weak-acid pH: [H⁺] ≈ √(Ka × C), then pH = −log[H⁺]
Buffers: weak acid + salt; pH = pKa + log([A⁻]/[HA])
Curves: half-equivalence gives pH = pKa; pick indicators over the steep region
You've covered Acid-base equilibria (AHL) for IB Diploma Chemistry HL. Press Finish to see your score.
You've worked through Acid-base equilibria (AHL) for IB Diploma Chemistry HL. 🎉
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Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.