Acids, Bases & Redox is a core part of IB Chemistry. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Brønsted acidProton donor
Brønsted baseProton acceptor
Conjugate baseAcid minus H⁺
pH-log₁₀[H⁺]
Kw[H⁺][OH⁻] = 10⁻¹⁴ at 298 K
NeutralpH 7 (at 298 K)
KaAcid dissociation constant
pKa-log Ka
KbBase dissociation constant
Ka × Kb = KwFor conjugate pair
Strong acidKa >> 1, pKa < 0
Weak acidKa << 1, pKa > 2
BufferResists pH change on adding acid/base
Henderson-HasselbalchpH = pKa + log([A⁻]/[HA])
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What is the difference between a strong acid and a concentrated acid?✗ They mean the same thing. ✓ Strong = fully ionised; concentrated = a lot of acid per volume.
What does neutralisation do?✗ Makes an acid more acidic. ✓ Moves the pH towards 7, forming a salt and water.
Which is the strongest acid?✗ pKa = 9.3 ✓ pKa = 3.2
What does oxidation mean in terms of electrons?✗ Only the gaining of oxygen, nothing else. ✓ Loss of electrons (OIL RIG: Oxidation Is Loss).
If E°cell for a redox reaction is positive, what does that tell you?✗ A positive E°cell guarantees the reaction will happen rapidly at room temperature. ✓ The reaction is thermodynamically feasible — but it may still be very slow if kinetic barriers are high.
Practise Acids, Bases & Redox — free games
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