Strong and weak acids and bases

Nature of science:

Improved instrumentation—the use of advanced analytical techniques has allowed the relative strength of different acids and bases to be quantified. (1.8)

Looking for trends and discrepancies—patterns and anomalies in relative strengths of acids and bases can be explained at the molecular level. (3.1)

The outcomes of experiments or models may be used as further evidence for a claim—data for a particular type of reaction supports the idea that weak acids exist in equilibrium. (1.9)

• Strong and weak acids and bases differ in the extent of ionization.
• Strong acids and bases of equal concentrations have higher conductivities than weak acids and bases.
• A strong acid is a good proton donor and has a weak conjugate base.
• A strong base is a good proton acceptor and has a weak conjugate acid.

Applications and skills:

• Distinction between strong and weak acids and bases in terms of the rates of their reactions with metals, metal oxides, metal hydroxides, metal hydrogen carbonates and metal carbonates and their electrical conductivities for solutions of equal concentrations.

Guidance:

• The terms ionization and dissociation can be used interchangeably.
• See section 21 in the data booklet for a list of weak acids and bases.

• The strength of an acid can be determined by the use of pH and conductivity probes. In what ways do technologies, which extend our senses, change or reinforce our view of the world?

Utilization:

• Syllabus and cross-curricular links:
• Topic 1.3—solution chemistry
• Topic 7.1—weak acids and basis involve reversible reactions

Aims:

• Aim 6: Students should have experimental experience of working qualitatively with both strong and weak acids and bases. Examples to include: H₂SO₄ (aq), HCl (aq), HNO₃ (aq), NaOH (aq), NH₃ (aq) .
• Aim 7: Students could use data loggers to investigate the strength of acid and bases.