Acids and bases: 8.40 - Strong and weak acids and bases

Syllabus ref: 8.4 Syllabus ref: 8.5

Acids and bases may be described as strong or weak. In this section we look at the meaning of these terms as specifically applied to these compounds. The way that they can be differentiated by property is outlined.

Nature of science:

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

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

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.

Risks and problems - oxides of metals and non-metals can be characterized by their acid-base properties. Acid deposition is a topic that can be discussed from different perspectives. Chemistry allows us to understand and to reduce the environmental impact of human activities.

Understandings

The pH depends on the concentration of the solution. The strength of acids or bases depends on the extent to which they dissociate in aqueous solution.

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.

Essential idea: Increased industrialization has led to greater production of nitrogen and sulfur oxides leading to acid rain, which is damaging our environment. These problems can be reduced through collaboration with national and intergovernmental organizations

Rain is naturally acidic because of dissolved CO₂ and has a pH of 5.6. Acid deposition has a pH below 5.6.

Acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO₃, HNO₂, H₂SO₄ and H₂SO₃.

Sources of the oxides of sulfur and nitrogen and the effects of acid deposition should be covered.

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.

Balancing the equations that describe the combustion of sulfur and nitrogen to their oxides and the subsequent formation of H₂SO₃, H₂SO₄, HNO₂ and HNO₃.

Distinction between the pre-combustion and post-combustion methods of reducing sulfur oxides emissions.

Deduction of acid deposition equations for acid deposition with reactive metals and carbonates.

In Chapter 8.4