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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

2.1.4 Acids

Acid–base titrations Acids, bases, alkalis and neutralisation

Acids, Bases, Alkalis and Neutralisation

Specification Reference 2.1.4 (a)–(c)

Quick Notes

  • Acid–Base Definitions
    • Acids: proton (H+) donors
    • Bases: proton (H+) acceptors
    • Alkalis: soluble bases that release OH− in solution
  • Strong and Weak Acids
    • Strong acids fully dissociate in water (e.g. HCl, HNO3, H2SO4)
    • Weak acids only partially dissociate (e.g. CH3COOH)
  • Neutralisation Reactions
    • Acid + metal oxide/hydroxide → salt + water
    • Acid + carbonate → salt + water + carbon dioxide
    • Acid + alkali → salt + water
  • Salt Preparation Techniques
    • Add excess base to acid
    • Filter unreacted base
    • Heat filtrate and allow to crystallise

Full Notes

Acids and Bases have been covered in more detail here
This is just what you need to know for OCR A-level :)

Acids, Bases and Alkalis

There are different ways we can define acids and bases in chemistry, however at this level the Brønsted–Lowry theory is used, which states:

An alkali is a base that dissolves in water, causing OH− ion concentration to increase.

Common acids you should know and remember include:

Common alkalis you should know and remember include:

Strong and Weak Acids

Strong acids completely ionise in water:

Example Hydrochloric Acid, HCl

HCl → H+ + Cl−
Each mole of HCl in solution breaks apart into H+ and Cl-

Weak acids only partially ionise:

Example Ethanoic Acid, CH3COOH

CH3COOH ⇌ CH3COO− + H+
Some CH3COOH remains in the solution, meaning there ends up being a mixture of CH3COOH, CH3COO− and H+ in the final solution.

This affects pH, reactivity, and conductivity. Strong acids generally produce lower pH values at the same concentration.

Neutralisation Reactions

Neutralisation involves the reaction of H+ from the acid with an OH− from an alkali to form water.

Example Acid + metal oxide (or hydroxide)

2HCl + CuO → CuCl2 + H2O

Example Acid + carbonate

2HCl + Na2CO3 → 2NaCl + H2O + CO2

Example Acid + alkali

HCl + NaOH → NaCl + H2O

The net-ionic equation for each of these reactions is:

OCR A-Level Chemistry example of full ionic and net ionic equation for HCl + NaOH with spectator ions highlighted.

The other ions from the acid and alkali combine to form a salt (for example Cl− and Na+ to form NaCl).

Summary