### Why do this problem?

This problem provides a good exercise in linking two areas of
mathematics: concentration and logarithms. Students will need to
flip between the two descriptions of acidity which will require
careful, clear thinking. The context is fascinating and this will
encourage a 'concrete' and practical engagement with logarithms.

### Possible approach

This question uses the advanced concept of logarithms but will
also use basic ideas about concentrations and mixtures. Students
will need to remember basic ideas about the meaning of a
'concentration' in order to work out the concentration of
mixtures.

### Key questions

What equations do you need to flip between the pH and the
concentration of $H^+$ ions?

How can you work out the concentration of a mixture of two
solutions?

### Possible extension

### Possible support

You might try and get started using the pH formula with the
problem

Temperature
pH