Virtual Experiments is a very useful website from Reading University that provides simulations of many standard school science experiments which can be carried out on your interactive whiteboard. The site is suitable for GCSE and also for A Level students.
Some of the experiments available include: Photosynthesis with Elodea, Transpiration, Reflection and Refraction, Chemical Clocks and looking at the Viscosity of Glycerol.
Most of the experiments have a full-screen option so that they work well on a whiteboard.
While simulations cannot and should not replace doing the experiment for real, they can provide useful ways of recapping or revisiting a practical. They are also useful if time is limited. Most of these simulations do not do the work for the students, they still need to count/measure and read from scales to collect their data.
Sadly, the experiments are in Flash, so you or your students can’t access them on an iPad. Hopefully they’ll change that in the future.
You can access the experiments here: http://www.reading.ac.uk/virtualexperiments/experiments.html