It can be tricky for students to appreciate what is going on in solution at the particle level that they cannot see. Charged ions, such as H⁺(aq) and OH^–(aq) can move, so acidic or alkaline solutions can conduct. The electrical conductivity of a solution depends upon the number of ions present in solution and their mobility. Conductivity measurements show evidence of ions in solution and provide another useful tool in exploring understanding of concentration and its link with pH.

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Conductivity measurements could be explored in the classroom by investigating the effect of dilution on the electrical conductivity of different concentrations of solution of a strong (fully ionised) acid. Consider the following student's example data:

What do you notice?

As the concentration of hydrated H⁺ ions and Cl^– ions in solution decreases, the conductivity of the solution decreases. This is not surprising because the number of ions in solution has decreased.

The student measured current – is that a problem?

As long as the voltage was kept the same the current will be proportional to the conductivity.

Some simulations are available online that show many aspects of acids and alkalis in solution, including visualisations of dilution and different concentrations of solutions that can be chosen. Have a go at a simulation from PhET Colorado on the pH scale.

While simulations are not a substitute for practical classroom activities, they can support them, for example by reinforcing tricky or key concepts. Here it is useful for helping to visualise the relative numbers or ratio of molecules and ions in solution of substances at a particular pH, and reinforces the logarithmic nature of the pH scale and the effect of dilution.