Chemistry study notes
Chemistry of Aqueous Solutions
Calculate acidity, follow titrations and buffers, and predict whether an ionic solid dissolves or precipitates.
A-Level 9476 (2026-2027)
Choose a topic
6 topicsAcid-base strength and equilibrium constants
Use dissociation extent, conjugate pairs and the ionic product of water.
Calculate pH
Choose the strong or weak approximation and check its assumptions.
Titration curves and indicators
Identify what controls pH before, at and after equivalence.
Buffers in calculations and oceans
Follow consumption of a small acid or base addition before using equilibrium.
Solubility and precipitation
Use Ksp and the ionic product with the correct dissolved-ion concentrations.
Common ions and silver-ammonia complexes
Explain why an added ion can suppress dissolution while complex formation promotes it.
Scope and references
Learning outcomes and sources
10. Chemistry of Aqueous Solutions. Use the outcome map to find the explanation for a particular syllabus requirement.
See the learning outcome map
10.1(a) Explain strong/weak acid and base behaviour.
- Extent of dissociation or reaction with water
- Strength distinguished from concentration and solubility
Strength is the extent of ionisation, not the amount dissolved
10.1(b) Define and calculate with acid-base equilibrium quantities.
- pH, Ka, pKa, Kb, pKb, Kw
- Kw = Ka Kb for a conjugate pair
- Temperature dependence of Kw
Constants connect an acid to its conjugate baseChoose the chemical model before taking a logarithm
10.1(c) Calculate hydrogen-ion concentration and pH.
- Strong acids
- Weak monobasic/monoprotic acids
- Strong bases
- Weak monoacidic bases
- No quadratic solving required
10.1(d) Explain acid-base titration pH changes.
- Strong and weak acid/base combinations
- Buffer, equivalence and excess regions
- Hydrolysis at equivalence
Different regions of a titration are controlled by different species
10.1(e) Choose indicators from supplied titration data.
- Transition interval within the steep pH change
- Endpoint versus equivalence
- Unfamiliar indicator ranges
Choose an indicator whose transition sits inside the steep change
10.1(f) Explain buffer action and applications.
- (i) Control of pH after small acid/base additions
- (ii) Uses including ocean CO3^2-/HCO3- buffering
- Rapid atmospheric CO2 increase and ocean acidification
- Finite buffer capacity
A buffer contains a reservoir for both added acid and added baseCarbonate buffering limits acidification but cannot stop unlimited carbon dioxide input
10.1(g) Calculate buffer pH.
- Acidic and alkaline buffer ratios
- Strong acid/base neutralisation before equilibrium calculation
Neutralise the added reagent first, then calculate the new ratio
10.2(a) Understand and apply the solubility-product concept.
- Saturated equilibrium with solid
- Free-ion product and precipitation criterion
A saturated solution has a fixed product of free-ion concentrations
10.2(b) Calculate Ksp from concentrations and vice versa.
- Dissolution stoichiometry
- Molar solubility
- Dilution on mixing
A saturated solution has a fixed product of free-ion concentrations
10.2(c) Explain changes in ionic-salt solubility.
- (i) Common-ion effect
- (ii) Complex formation
- Halide ions with aqueous silver ions then aqueous ammonia
- Free versus total dissolved ion
A common ion and a ligand pull the dissolution equilibrium in opposite directions
- SEAB H2 Chemistry 9476, examination 2026
Topic 10, printed pages 22-23. Seven acid-base and three solubility outcomes, including the current ocean-buffer requirement and all silver-halide/ammonia observations, inspected.