Topic 14
Acid-base
Equilibria
Topic 14 treats acids and bases as equilibria. It defines Brønsted–Lowry acids, bases and conjugate pairs, calculates pH for strong and weak acids and strong bases using Ka and Kw, analyses pH measurements and dilution data, draws and interprets titration curves (including diprotic acids and bases) to choose indicators and find Ka, and explains how buffers work, how to calculate and prepare them, and why they matter in blood, cells and foods. It is examined in Unit 4.
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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Titration Curves and Indicators
Titration 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 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
Edexcel International A Level Chemistry · Unit 4 · Topic 14A 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
Edexcel International A Level Chemistry · Unit 4 · Topic 14B Weak Acids
The whole section on one A4 page: weak acids, Kₐ and pKₐ, the pH of a weak acid, measuring pH and finding Kₐ by experiment.
Titration Curves Map
Edexcel International A Level Chemistry · Unit 4 · Topic 14C Titration Curves and Indicators
The whole section on one A4 page: measuring a titration curve, strong and weak acids and bases, diprotic curves and choosing an indicator.
Buffers Map
Edexcel International A Level Chemistry · Unit 4 · Topic 14D Buffer Solutions
The whole section on one A4 page: what a buffer is, how it works, calculating buffer pH, making a buffer, and buffers in blood, cells and food.
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Specification
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Self-assessment · 42 points
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14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.8
14.9
14.10
14.11
14.12
14.13
- i a
be able to analyse data from the following experiments: measuring the pH of a variety of substances, including equimolar solutions of strong
Revise - i b
be able to analyse data from the following experiments: measuring the pH of a variety of substances, including weak acids
Revise - i c
be able to analyse data from the following experiments: measuring the pH of a variety of substances, including strong
Revise - i d
be able to analyse data from the following experiments: measuring the pH of a variety of substances, including weak bases
Revise - i e
be able to analyse data from the following experiments: measuring the pH of a variety of substances, including salts
Revise - ii
be able to analyse data from the following experiments: comparing the pH of a strong and weak acid after dilution 10, 100 and 1000 times
Revise
14.14
- 14.14
be able to calculate Ka for a weak acid from experimental data given the pH of a solution containing a known mass of acid
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14.15
14.16
14.17
14.18
14.19
14.20
- 14.20
be able to calculate concentrations of solutions required to prepare a buffer solution of a given pH
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14.21
- i
understand how to use a weak acid-strong base or strong acid-weak base titration curve to: demonstrate buffer action
Revise - ii
understand how to use a weak acid-strong base or strong acid-weak base titration curve to: determine Ka from the pH at the point where half the acid is neutralised/ equivalence point
Revise
14.22
14.23
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