CHEMISTRY
I follow a similar procedure for the production and testing of hydrogen: explain, show, use MWB supports, check for understanding. Following this, students are ready for independent practice, and among more straightforward ones, I will ask questions like: • What are the differences and similarities between testing for carbon dioxide and testing for hydrogen? • A student says to test for carbon dioxide, you add calcium carbonate to limewater. Explain why the student is wrong. • A student wants to test for carbon dioxide and mixes calcium oxide with hydrochloric acid. Explain why this would not work. • In the limewater test we did, where is the calcium chloride at the end of the reaction? • Where is the water at the end of the reaction? • Where is the carbon dioxide at the end of the reaction? • A student is asked: Describe how you can test for hydrogen And answers: Use the squeaky pop test Explain why the student’s answer is not good enough. • Complete the table below: Gas test
Result
Conclusion
Squeaky pop Limewater does not change
Carbon dioxide is not present
Bubble through limewater Hydrogen is not present These aren’t necessarily “exam questions,” but they do promote deeper thought about the tests. In sum, we are now much closer to our stated aim of having students not only able to recall the gas tests accurately, but to better understand the process that enable them, the similarities and differences between them, and the correct language to employ when describing them.
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