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pH Temperature

Stage: 5 Challenge Level: Challenge Level:1

Why do this problem?

This problem involves the application of logarithms to pH. This interesting application, in which the critical value of pH 7 is familiar, will give a good motivation for engaging with the logarithm.

Possible approach

To do this question, students will need to understand the precise mathematical meaning of both the dissociation constant and the pH (both are clearly described in the question, so no particular knowledge of chemistry is required). Initially students might need to think on how they can connect the various pieces of information.

Key questions

What equations will you need to use to solve the problem?
How can you use the table of data in the question?
Why is an approximation in the question needed? At what point in a question will an approximation be made?

Possible extension

Students will need to interpolate the data in the table to be able to provide an approximation. Can they suggest differentpossibilities for this interpolation? Which one is best?

The next question in this series is extreme dissociation

Possible support

Ask the students to work out the pH at the different temperatures given in the table.