For Day 92, I introduced a new practicum for Unit 7: determining the formula of a hydrate. I presented my students with the compound copper (II) sulfate and told them it had a certain number of water molecules embedded in the lattice. I told them their job was to figure out how many water molecules surround each copper (II) sulfate compound.
We came up the experimental design as a class: heat the powder in a crucible, mass it, heat it again, mass it again, repeat until the mass stabilizes. I left it up to each group to determine how they would go about their calculation.
Honestly, I thought I would stump students a bit with this one but they finished it in record time with decent results!