3.1.12
Acids and
Bases
Section 3.1.12 covers the Brønsted–Lowry theory, the pH scale and the pH of strong acids, the ionic product of water and the pH of strong bases, weak acids with Ka and pKa, pH curves for the four combinations of strong and weak acids and bases, titration calculations and the choice of indicator, and acidic and basic buffers, how they work and how to calculate the pH of an acidic buffer. Required Practical 9 is covered on the last page.
Revision Notes
8 revision notes, in the order the specification teaches them.
Brønsted–Lowry Acids, Bases and Conjugate Pairs
Brønsted–Lowry acids and bases: proton donors and acceptors, proton transfer, conjugate acid-base pairs and water as an acid and a base.
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pH and Strong Acids
PH and strong acids: pH = −log[H⁺], [H⁺] = 10⁻ᵖᴴ, strong and weak acids, and calculating the pH of strong acids.
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The Ionic Product of Water, Kw, and Strong Bases
The ionic product of water: Kw = [H⁺][OH⁻], pKw, the effect of temperature on Kw and neutral pH, and the pH of strong bases.
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Weak Acids: Ka and pKa
Weak acids: the Ka expression, pKa, calculating the pH of a weak acid, finding Ka from pH, and the limits of the approximations.
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pH Curves and Indicators
PH curves and indicators: the four acid-base combinations, equivalence points, pKa from half-neutralisation and choosing a suitable indicator.
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Buffer Solutions: How They Work and Why They Matter
Buffer solutions: making acidic and basic buffers, how a buffer resists pH change, and the blood buffer system.
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Calculating the pH of a Buffer Solution
Calculating buffer pH: [H⁺] = Ka × [HA]/[A⁻], buffers by partial neutralisation, making a buffer of a given pH, and pH after adding acid or alkali.
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Measuring pH and Finding Ka by Experiment
Measuring pH and finding Ka: the pH meter, pH of acids, bases and salts, dilution of strong and weak acids, and the half-neutralisation method.
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Acids, Bases and pH Map
AQA A-level Chemistry · 3.1.12.1–3.1.12.3 Acids, bases and pH
The whole section on one A4 page: Brønsted–Lowry acids and bases, conjugate pairs, pH, strong acids, the ionic product of water and strong bases.
Weak Acids Map
AQA A-level Chemistry · 3.1.12.4 Weak acids
The whole section on one A4 page: weak acids, Kₐ and pKₐ, the pH of a weak acid and finding Kₐ by experiment.
pH Curves Map
AQA A-level Chemistry · 3.1.12.5 pH curves, titrations and indicators
The whole section on one A4 page: measuring a pH curve, strong and weak acids and bases, titration calculations and choosing an indicator.
Buffers Map
AQA A-level Chemistry · 3.1.12.6 Buffer action
The whole section on one A4 page: what a buffer is, how it works, calculating buffer pH, making a buffer and buffers in the body.
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3.1.12.1
3.1.12.2
- i
understand that the pH scale is a logarithmic measure of hydrogen ion concentration: pH = -log10[H+]
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3.1.12.3
- i
know that water is slightly dissociated and that Kw is derived from the equilibrium constant for this dissociation
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3.1.12.4
- v
perform calculations relating the pH of a weak acid to the concentration of the acid and the dissociation constant Ka
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3.1.12.5
3.1.12.6
- i
know that a buffer solution maintains an approximately constant pH despite dilution or addition of small amounts of acid or base
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