Buffers exploit the pairing; titrations map it, and the curve's landmarks, equivalence, half equivalence, name the chemistry. The tool below drills the map.
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Unit 8 proton ledger, from your own notes
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Strength is a dissociation verdict, not a danger rating
A strong acid transfers its proton to water completely, so hydronium equals the acid's concentration and pH is one log away; a weak acid equilibrates, and the Ka sizes how far. Percent ionisation falls as concentration rises, a tested subtlety. The strong list is short and memorised; everything else negotiates, and the ICE machinery from the equilibrium unit does the arithmetic.
Conjugate pairs are one proton apart, and their constants multiply
Every acid has a conjugate base one proton lighter, and the pair's constants obey Ka times Kb equals Kw: a stronger acid necessarily has a feebler conjugate base. This single identity powers salt questions, a salt solution inherits its pH from the stronger surviving parent, ammonium chloride acidic, sodium acetate basic, and it is why the same table answers acid and base problems both directions.
Buffers: a pair on duty absorbs the insult
A buffer stocks both partners, weak acid to eat added base, conjugate base to eat added acid, so pH moves slightly where pure water would swing. Henderson Hasselbalch reads the pH from the ratio around pKa, capacity runs out when one partner does, and design questions want the acid whose pKa sits nearest the target pH. State the pair and which partner answers which insult: that sentence is the rubric.
Titration curves confess the chemistry
A titration curve's shape names the system: strong strong crosses seven at equivalence; weak acid strong base starts higher, buffers through the middle, and ends basic because the conjugate base remains. Half equivalence is the confession, pH equals pKa there, and equivalence volume gives the unknown concentration. Polyprotic acids stack one wave per proton. Read landmarks first, calculate second.
Indicators and the lab's judgement calls
An indicator is itself a weak acid whose colour change brackets its own pKa, so you pick the one that flips at the expected equivalence pH, phenolphthalein for weak acid strong base, not universally. The lab questions grade judgement: which indicator, why the curve's steep region tolerates indicator error, and how diluting a buffer changes capacity but not ratio. Each is a one sentence justification the rubric names.
What to photograph for Acids and Bases
Your Ka tables and labelled curves. Related: Unit 7, photo to quiz and pricing.
Sources used on this page
- College Board, AP Chemistry
- pH
- Acid dissociation constant
- Buffer solution
- Titration
- Active recall
- Spaced repetition
- Testing effect
- Forgetting curve
- Generation effect
- Judgment of learning
- Metacognition
- Desirable difficulty
- Distributed practice
- Formative assessment
- Flashcard
- Cloze test
- Multiple choice
- Test (assessment)
- Educational assessment
- Advanced Placement
- Curriculum
- Study skills
- Study guide
- Note-taking
- Overlearning
- Instructional scaffolding
- Item analysis
- Mastery learning
| System | The landmark | What it tells |
|---|---|---|
| Strong acid solution | Full dissociation | pH by one log |
| Weak acid solution | Ka and ICE | Percent ionisation |
| Conjugate salt | Stronger parent wins | Acidic or basic verdict |
| Buffer | Ratio around pKa | Small pH moves |
| Weak strong titration | Half equivalence | pH equals pKa |
| Equivalence point | Stoichiometry done | Unknown concentration |
What does AP Chemistry Unit 8 cover?
Acid base chemistry: strength and Ka, pH, conjugate pairs, buffers, titration curves, salts and indicators.
What separates strong from weak acids?
Dissociation: strong acids transfer protons completely, weak ones equilibrate with a Ka that sizes the negotiation.
How does a buffer actually work?
Both partners stand ready: the weak acid neutralises added base, the conjugate base neutralises added acid, so pH moves only slightly.
Why does pH equal pKa at half equivalence?
Half the acid has been converted to conjugate base, so the ratio is one and Henderson Hasselbalch collapses to pKa.
Why is weak acid strong base equivalence basic?
At equivalence only the conjugate base remains, and it hydrolyses water enough to lift the pH above seven.
Can I build questions from my own Unit 8 notes?
Yes. Photograph the pages or upload the PDF and the questions stay inside this unit rather than sampling the whole course.
Last updated: 2026-08-15