My Year 12 Chemistry students were testing for cations and anions the other day. Today they were applying some of what they had learnt to determine the identity of a set of unknown solutions (A – D).
They were told that their set contained four solutions – HCl, Na2CO3, Ca(NO3)2 and Pb(NO3)2 – but that they didn’t know which was which. Their task was to combine these four solutions in particular combinations to work out the identity of each one, using their previous results to guide them as to how to detect particular ions.
It went really well! The practical component was very straightforward to carry out but it was the interpretation of their results that required some really mental effort. Some really wrestled with it and eventually worked out which was which, whereas other groups didn’t quite get it finished in time before we had to come back to discuss it together. Here is one group’s whiteboard of their data and interpretation: