Unit P3: Equilibrium II: Acids and Bases

Equilibrium II: Acids and Bases was one of the physical chemistry units in the Independent Learning Project for Advanced Chemistry (ILPAC) scheme that was sponsored by the Inner London Education Authority and first published by John Murray in 1983. This was a study guide, not a textbook.

In level one, this unit takes a mainly qualitative approach, using the Bronsted-Lowry theory to define acids and bases. The application of Le Chatelier 's principle to acid-base equilibria is illustrated. The acid dissociation constant is introduced as a measure of the strength of an acid.

Level two covers much the same material but from a more mathematical stand point. The text applies the equilibrium law to systems involving weak acids, weak bases, buffer solutions and indicators.

Contents

Level one
Hydrogen ions
* Size of hydrogen ions
* Hydrogen ions in solution
* Attraction of hydrogen ions by other centres of negative charge

The Bronsted-Lowry theory
* Conjugate acid -base pairs

Ionisation of water
* The ionic product of water
* Using the expression for the ionic product of water
* The effect of temperature on Kw

pH, the hydrogen ion exponent
* The pH scale
* Calculating pH from hydrogen ion concentration
* Calculating hydrogen ion concentration from pH

Relative strengths of acids
* Experiment 1 - the pH of a weak acid at various concentrations
* Experiment 2 - the pH of different acids at the same concentration
* Dissociation constants of acids
* Calculating Ka from hydrogen ion concentration (or from pH)

* Calculating pH from the dissociation constant

Buffer solutions (1): controlling the pH
* Experiment 3 - the action of a buffer solution
* Composition of buffer solutions
* How acid buffers absorb hydrogen ions and hydroxide ions
* Buffer solutions and the equilibrium law

Historical development of acid-base theories

Level two
Acid-base indicators
* Experiment 4 - determining the pH range of some acid-base indicators
* Indicators as weak acids
* End-point and equivalence point
* Choice of indicator
* Calculating the pH range of an indicator
* Measurement of ionization constant values for indicators
* Experiment 5 - determining the ionization constant for an indicator

pH changes during titrations
* Experiment 6 - obtaining pH curves for acid-alkali titrations
* pH curves by calculation

Hydrolysis of salts

Buffer solutions (2)
* Buffering regions of titration curves
* pH of a buffer solution
* The relationship between pH , Ka and the composition of a buffer

* Calculating the composition of a buffer from pH

Experiment 7 - preparation of buffers: testing their buffering capacity and the effect of dilution
Experiment 8 - determining the dissociation constant for a weak acid using an indicator

Appendix one
Additional exercises

Appendix two
Calculating the pH of salt solutions

Answers to exercises

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