This lesson develops the concepts peculiar to acid-base equilibrium in water. It starts by introducing the self-ionization reaction, and establishes the equilibrium concentrations of H3O+ and OH- in pure water. Now "acidic" and "basic" solutions have a more precise meaning. There is an exercise in calculating one of [H3O+] and [OH-] given the value of the other.
The pH scale is introduced. One is shown how to deduce pH from [H3O+], using the on-screen calculator. There is a well-coached exercise in which one learns how to estimate pH to one decimal place (as much accuracy as is usually significant). The drill at the end requires the student to estimate the pH on a 0 to 15 scale before actually calculating it.
The relationships among pH, pOH, and pKw are developed, and one sees how to recognise acidic, basic and neutral solutions on both scales.
The inverse relationship between the strength of an acid or base and the strength of its conjugate is developed qualitatively. It is shown that strong acids have very weak conjugate bases and vice versa - so one may immediately recognise that Cl- is a very weak base, and that H- and OCH3- are strong bases. The KaKb = Kw relationship is developed, and a table of dissociation constants presented, contrasting conjugates. There is a drill in which the student are shown the directions of related acid-base reactions, and must use this information to rank by strength the acids or bases involved.
The final review quiz is a simple assignment: fill in the twelve missing entries in the table shown above. The dissociation constants may be inferred from the reciprocal relationship of Ka and Kb, the formulas from the Bronsted definitions, and the name of "coniinium" should be evident by analogy. The student may return to the earlier parts of the lesson and return without losing parts of the table that are already completed.
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Updated July 6, 2001