The Joy of Open-Ended Challenges
What IS the effect of impurities on ice? This lab highlights the old dilemma of how much freedom can you give students without chaos ensuing? Because choice is directly linked to engagement, and that means students are really thinking about the concepts they need to understand in order to meet the challenge.
I took a risk, opened cupboards of containers, got in a load of ice, salt, sugar and sand. Scales, tablespoons, measuring cylinders and thermometers were available. The rule was ‘return the lab to this state by the end of the period’, and a consideration of basic safety precautions (slipping on ice and water, irritants in eyes – trip hazards were removed, protective eye wear required).
Set the challenge “What is the effect of impurities on ice?” Showed them the materials and equipment and had a sheet where they recorded their experimental question, hypothesis, the variables, drew a diagram of their set-up and a data table. That’s their pass to start. Then they did it. Some fails and re-starts. Especially around not being clear what they were going to observe or measure. Just waiting for ice cubes to melt. Boring. Better to measure melt water every couple of minutes, or temperature over time. Here are some pics of what they did.
The big win was this absolutely intent atmosphere with every group working hard, on task. Well, the usual suspects still trying not to do anything, but in general, great level of engagement and curiosity.
I did give lab points for clean up and it was no worse than usual. btw, have a bucket for the sand – it will clog up sinks. Everything else can go down the sink. Wipe tables after class to prevent ants and general stickiness.
As they got their data, the group ‘recorders’ came up and wrote in what the effect of each impurity was on their ice. Very quick and easy way of putting the results together for the class – that dissolved substances depress the melting point of ice, and drop the temperature. Sand, which doesn’t dissolve, does not. Boom. Done. Fun.
Entry filed under: Chemistry topics, Particulate Theory, Thermodynamics. Tags: 8th grade science, challenge based lab, lab science, melting points, physical chemistry, physical science, teaching ideas.