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Acids and bases (A-level only)
This A-level-only topic develops quantitative and qualitative acid-base chemistry.
20
Objectives
100
Flashcards
94
Questions
90 min
Study time
AQAA LevelChemistryPhysical chemistry
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Syllabus checklist
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20 objective pages available
Brønsted-Lowry acids and bases (A-level only)4 objectives
- Define Brønsted-Lowry acids and bases.
- Identify conjugate acid-base pairs.
- Write equations showing proton transfer.
- Distinguish acid strength from concentration.
pH and Kw (A-level only)4 objectives
- Calculate pH from hydrogen ion concentration.
- Calculate hydrogen ion concentration from pH.
- Use Kw to calculate hydrogen ion or hydroxide ion concentrations.
- Apply pH calculations to strong acids and strong bases.
Weak acids, Ka and pKa (A-level only)4 objectives
- Construct Ka expressions for weak acids.
- Calculate pH of a weak acid from concentration and Ka.
- Convert between Ka and pKa.
- Explain weak-acid behaviour in terms of partial dissociation.
pH curves, titrations and indicators (A-level only)4 objectives
- Perform calculations using acid-base titration data.
- Sketch and explain pH curves for combinations of weak and strong monoprotic acids and bases.
- Select suitable indicators using pH curves and transition ranges.
- Required practical: investigate pH changes in weak acid and strong base or strong acid and weak base titrations.
Buffer action (A-level only)4 objectives
- Explain qualitatively how acidic buffers resist pH change.
- Explain qualitatively how basic buffers resist pH change.
- Calculate the pH of acidic buffer solutions.
- Explain applications of buffer solutions.
Key terms
Brønsted-Lowry acidBrønsted-Lowry baseAcid StrengthAcid ConcentrationpHhydrogen ion concentrationKwhydroxide ion concentrationstrong acidKa expressionweak acidKa
Exam tips
- Understanding Brønsted-Lowry Acids and Bases: Explain clearly by define Brønsted-Lowry acids as proton donors and bases as proton acceptors. Link the point to Brønsted-Lowry acids and bases (A-level only), then state the evidence, calculation, mechanism, observation, or conclusion required by the question.
- Identifying Conjugate Acid-Base Pairs: When identifying conjugate acid-base pairs, remember that a conjugate acid is formed when a base gains a proton, and a conjugate base is formed when an acid loses a proton.
Common mistakes
- Misunderstanding Brønsted-Lowry Definitions: Remember that Brønsted-Lowry acids are defined as proton donors and bases as proton acceptors. For example, in the reaction HCl + H2O → Cl- + H3O+, HCl donates a proton to water, making it a Brønsted-Lowry acid.
- Identifying Conjugate Pairs: To correctly identify conjugate acid-base pairs, remember that a conjugate acid is formed when a base gains a proton (H⁺), and a conjugate base is formed when an acid loses a proton. For example, in the reaction HCl + H₂O ⇌ Cl⁻ + H₃O⁺, HCl is the acid and Cl⁻ is its conjugate base, while H₂O is the base and H₃O⁺ is its conjugate acid.
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