Geo already posted address of my website (I was reluctant to do so, as BATE - which can be used for such a lab - is a commercial product).
However, take a look at http://www.chembuddy.com/files/diffusion.zip
- small (and free) program that simulates diffusion (it is based on idea published back in eighties in Journal of Chemical Education). The faster the computer - the better (although 600MHz will be enough if you are patient).
I think you can use it for an interesting lab - finding dependence between time needed to end the simulation and the window height (while diffusion model is very simplified, results are in accordance with theoretical predictions). Window height plays a role of solution thickness here (to speed up the simulation make the window high, but narrow). End of the simulation is the moment when the anode and cathode are connected by the dendrites (*%^*%^, how to name this moment in English?)Edit:
ops, sorry - diffusion is not a gas laws, pH nor kinetics