Acids & Bases
Learn and apply Acids & Bases in the published Chemistry course sequence.
Learning goals
- Arrhenius, Brønsted–Lowry, Lewis Definitions
- Conjugate Pairs and Amphoteric Species
- Lewis Adducts and Exam Phrasing
H2 Acids and Bases (Theories) learning outcomes
This hub covers the three acid–base theories required in Topic 4. The models overlap, so the task is not always to choose only one: apply the theory named in the question and use its exact evidence and vocabulary. Acid strength, pH and equilibrium calculations live in Chemistry of Aqueous Solutions.
Before you start
Beginner path: follow the Lessons (Recommended Order) from top to bottom.
Revision: Jump to: Quick Reference · What You Must Memorise · Common Exam Traps · Hub Quiz.
Prerequisites: skim the Prerequisites list first if you’re rusty.
Useful links: A Level portal · Exam Skills
What You’ll Learn
- Apply the Arrhenius theory to acids and bases in aqueous solution.
- Apply the Brønsted–Lowry theory, including conjugate acids and conjugate bases.
- Apply the Lewis theory, including the required non-aqueous reaction between BF₃ and NH₃.
- Recognise when one reaction can be described by more than one theory and use the vocabulary requested.
Lessons (Recommended Order)
Arrhenius, Brønsted–Lowry, Lewis Definitions
Apply each theory and recognise where the models overlap.
Conjugate Pairs and Amphoteric Species
Identify conjugates and prove amphiprotic behaviour with equations.
Lewis Adducts and Exam Phrasing
Adduct formation, arrow direction, and donor/acceptor keywords.
Quick Reference
- Arrhenius (aqueous only): an acid produces H⁺ or H₃O⁺ in water; a base produces OH⁻ in water. State the ion produced.
- Brønsted–Lowry: an acid donates a proton; a base accepts a proton. Show which species loses or gains one H⁺.
- Lewis: an acid accepts an electron pair; a base donates an electron pair. Draw any coordinate-bond arrow from the donor to the acceptor.
The theories can overlap. For example, NH₃ is a Brønsted–Lowry base when it accepts a proton and a Lewis base because its lone pair forms the new bond.
Quick default examples (quote these under exam pressure):
- Brønsted–Lowry: NH₃ + H₂O ⇌ NH₄ + + OH⁻
- Lewis adduct: :NH₃ → BF₃
What You Must Memorise
- Arrhenius acid/base (aq): produces H⁺ / OH⁻ in water.
- Brønsted–Lowry acid/base: proton donor / proton acceptor.
- Lewis acid/base: electron-pair acceptor / electron-pair donor.
- Conjugate pair: differs by exactly one H⁺.
- Amphiprotic: can donate and accept H⁺. Such a species is amphoteric under the Brønsted–Lowry model; show both roles with equations.
Hub Quiz and Check Your Understanding
Use practice in two passes: first without notes, then return to the lesson covering the idea you found difficult.
Acids and Bases Theories Hub Quiz
Check Arrhenius, Brønsted–Lowry and Lewis theory, conjugate pairs and adduct language.
H2 Acids and Bases Theory Knowledge Check
Find the idea that needs more work, use the feedback, then try a fresh question independently.
Practise
Work through questions with marking and feedback as you learn.
About 10 minutes
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Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.
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Beyond the syllabus: optional enrichment that does not count towards your progress.
Practise after feedback
After a check, practise the skills it showed you need to work on.
About 10 minutes
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Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.
Recent attempts
History is stored only in this browser.
No completed attempts are saved yet.
Beyond the syllabus: optional enrichment that does not count towards your progress.
Check what I know
Start here to see which parts you already know.
About 8 minutes
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Answer 5 short questions. It shows what to work on next and doesn't count towards mastery.
Recent attempts
History is stored only in this browser.
No completed attempts are saved yet.
Beyond the syllabus: optional enrichment that does not count towards your progress.
Check my progress
When you feel ready, answer on your own to show what you can do.
About 10 minutes
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Answer 5 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.
Recent attempts
History is stored only in this browser.
No completed attempts are saved yet.
Beyond the syllabus: optional enrichment that does not count towards your progress.
Check again
After practising what your progress check showed, check those skills again.
About 10 minutes
Time is up, but your answers have not been submitted yet. Check your connection and try again.
Answer 5 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.
Recent attempts
History is stored only in this browser.
No completed attempts are saved yet.
Beyond the syllabus: optional enrichment that does not count towards your progress.
Review
Come back later to see whether your learning has lasted.
About 10 minutes
Time is up, but your answers have not been submitted yet. Check your connection and try again.
Answer 5 questions. You'll see your score, the answers and explanations at the end. A scheduled review counts towards your course progress only when it is due.
Recent attempts
History is stored only in this browser.
No completed attempts are saved yet.
Beyond the syllabus: optional enrichment that does not count towards your progress.