The pH of very dilute solutions of strong acids – a calculation for a medical or biomedical class involving the application of simple numerical skills

This paper presents the solution to a calculationof the pH of a very dilute solution of a strong acid orbase, taking into account the effect of the hydroniumor hydroxyl ions generated from the ionisation of thestrong acid or base on the ionisation of water, as asecond very weak acid. To be solved successfully, thiscalculation involves the concepts of conservation ofcharge, pH and the application of the general solutionto a quadratic equation. Such an exercise involves theapplication of skills in basic numeracy, and can providea core of understanding that can prepare students formany different sorts of calculations that represent reallifeproblems in the medical and biological sciences.A programme is presented in C++ which enables thework of students to be individualised so that eachstudent in a class can work through a slightly differentpH calculation, in such a way that a class supervisorcan quickly check each student’s result for accuracy.This exercise is presented as a potential means ofenabling students to undertake and master similartypes of calculations involving simple or more complexequilibria.