How does the mass of a soda can change?

I get one of the students to accurately weigh a can of soda (to 2 decimal places). I then get them to open the can and weigh it every 5 min or so throughout the lesson. This allows a good talking point about how often you should take a measurement. The students seem to really engage with this real life example of particle theory. There is a lot of opportunity for getting the students to find problems with the diagram and improve on it demonstrating higher order thinking.