Use the units to check that they’ve actually done the right calculation. The other thing is when they’ve got the mole concept and they’re applying it, try to get students to do an estimation of the answer. So are they estimating something that’s very large?
They’re stepping into an area where they must do calculations and they must support them with strictly mathematical algebra, so that when they’re doing calculations it’s clear what the data is and what the units are and how these all fit together to make up the calculation they’re doing. So it’s really about making things mathematically strict.
Use clicker questions in a lecture. Use multiple choice questions and you can see the class distribution, that is, what percentage of students got it right. If a lot of them don’t get it right, go through it again. That really helps to get the feedback from students about their understanding. Use it for other topics as well but this will be one topic to use it for in a big class.
Use Roy Tasker’s video model VisChem, or Kahn Academy, and post on Blackboard. There are a lot of online formative practise quiz questions, for example, in Kahn Academy.
Use Lego pieces. For example, HCl built out of Lego. Use a little blue brick and a yellow one, showing physically that on this side you’ve got one blue Lego brick and then on this side you’ve got two and so on, trying to make them see them not as chemical formulas but identities of some sort.
In the lab you can get students to weigh out quantities and react them and then do calculations for the yield, so they’re applying it. That’s the way in which they come to terms with what they’re actually doing and the molar basis for that. It’s about representing what’s going on, on a molecular basis. We handle things on a molar basis because they’re the amounts we can weigh, and it’s representative of what’s going on on the molecular scale. It’s just scaled up by 6 x 1023.
Try demonstrating the reaction first, to show the macroscopic changes that occur, before introducing the equation. Copper in silver nitrate solution is a standard one. Explain it in terms of particles, the ions, atoms, show a video representation (for example from YouTube) of these changes, and then explain the whole thing in terms of the symbolic chemical equation to represent the overall change.
