Hi Edel,
I love that science fact too in relation to the grains of sand and the number of stars – it really does help us visualise the vastness of space.
I like your inquiry based learning activity and all the variables with regard to melting ice and prior predictions. I have used salt and ice and food dye in the past particularly where it has been a cold winter and the roads have been gritted and I wanted the children to understand the impact of the salt on ice. However, I really like the idea though of including more variables and predictions and analysing the outcomes for this type of experiment – I will do this for sure next time round.