5.1.3
Acids, Bases
and Buffers
Section 5.1.3 covers Brønsted–Lowry acids and bases, conjugate pairs and the basicity of acids, the role of H⁺ in acid reactions, Ka and pKa, pH and the ionic product of water, pH calculations for strong acids, strong bases and weak acids and the limits of the approximations, buffer solutions, how they are made and how they control pH, the blood buffer, pH titration curves and indicators, and measuring pH with a pH meter.
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, and the basicity of acids.
Start revising
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.
Start revising
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.
Start revising
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.
Start revising
pH Titration Curves and Indicators
PH titration curves and indicators: the four acid-base combinations, equivalence points, pKa from half-neutralisation and choosing a suitable indicator.
Start revising
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.
Start revising
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.
Start revising
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.
Start revisingSummary Map
Download, print and revise the key facts of this topic at a glance.
Summary maps
Download, print and revise the key facts of this topic at a glance.
Acids, Bases and pH Map
OCR A Level Chemistry A · 5.1.3 Acids, bases and pH
The whole section on one A4 page: Brønsted–Lowry acids and bases, basicity and the reactions of acids, pH, strong acids, Kw and strong bases.
Weak Acids Map
OCR A Level Chemistry A · 5.1.3 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.
Titration Curves Map
OCR A Level Chemistry A · 5.1.3 pH titration curves and indicators
The whole section on one A4 page: measuring a pH titration curve, strong and weak acids and bases, titration calculations and choosing an indicator.
Buffers Map
OCR A Level Chemistry A · 5.1.3 Buffer solutions
The whole section on one A4 page: what a buffer is, how it works, calculating buffer pH, making a buffer, and blood pH.
© 2026 Online Learning System. For personal study: printing is allowed; editing, copying and redistribution are not.
Virtual Lessons
Recorded video lessons that teach the topic step by step.
The Virtual Lessons for 5.1.3 Acids, Bases and Buffers are being recorded.
MCQ Bank
Multiple-choice papers on this topic, marked the moment you submit.
The MCQ papers for 5.1.3 Acids, Bases and Buffers are being written.
SAQ Bank
Written, drawn and worked exam practice on this topic.
The exam practice papers for 5.1.3 Acids, Bases and Buffers are being written.
Revision Game
Match reagents to products, with your board's reagents and conditions.
The revision game for 5.1.3 Acids, Bases and Buffers is being built.
Study Cards
Pick a deck, then turn each card to check what you remember.
Specification
Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.
Self-assessment · 32 points
Sign in to rate how confident you feel about each point. Your ratings are saved to your account, follow you to any device, and appear beside your KASP analytics, kept apart from your marks.
5.1.3
- b i
the role of H+ in the reactions of acids with metals, using ionic equations (see also 2.1.4 c, 2.1.5 e)
Revise - b ii
the role of H+ in the reactions of acids with carbonates, using ionic equations (see also 2.1.4 c, 2.1.5 e)
Revise - b iii
the role of H+ in the reactions of acids with metal oxides, using ionic equations (see also 2.1.4 c, 2.1.5 e)
Revise - b iv
the role of H+ in the reactions of acids with alkalis, using ionic equations (see also 2.1.4 c, 2.1.5 e)
Revise - c (i)
the acid dissociation constant, Ka, for the extent of acid dissociation (see also 2.1.4 b)
Revise - i
a buffer solution as a system that minimises pH changes on addition of small amounts of an acid or a base
Revise - j (i)
formation of a buffer solution from a weak acid and a salt of the weak acid, e.g. CH3COOH/CH3COONa
Revise - j (ii)
formation of a buffer solution from excess of a weak acid and a strong alkali, e.g. excess CH3COOH/NaOH
Revise - k
explanation of the role of the conjugate acid–base pair in an acid buffer solution, e.g. CH3COOH/CH3COO–, in the control of pH
Revise - l i
calculation of the pH of a buffer solution, from the Ka value of a weak acid and the equilibrium concentrations of the conjugate acid–base pair
Revise - n (i) a
sketch of the shapes of pH titration curves for combinations of strong and weak acids with strong and weak bases
Revise - n (i) b
interpretation of the shapes of pH titration curves for combinations of strong and weak acids with strong and weak bases
Revise - n (iii)
explanation of indicator colour changes in terms of equilibrium shift between the HA and A– forms of the indicator
Revise
Keep this note — free
Save your progress across every OCR topic. A free account remembers which topics you have covered, saves your question scores, and syncs across your phone and laptop.
- Track every topic you have finished
- Keep your practice-question scores
- No payment, no card, free forever
Already registered? Log in