When calcium carbonate is heated it breaks down into smaller products, one of which is a gas
The mass of calcium carbonate can be used to determine the number of moles of calcium carbonate at the start. The balanced chemical equation shows that for every mole of calcium carbonate that decomposes (breaks down), one mole of carbon dioxide gas is produced. The number of moles of carbon dioxide can then be used to determine the volume produced.
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Use this student worksheet to help learners think about relative formula mass, reacting ratios and gas volumes in the context of decomposition reaction.
View and download more Johnstone's triangle worksheets
Learning objectives
- Understand the term ‘thermal decomposition’.
- Calculate relative formula mass.
- Calculate the volume of a product from the mass of a reactant.
How to use Johnstone’s triangle
Use Johnstone’s triangle to develop learners’ thinking about scientific concepts at three different conceptual levels:
- Macroscopic – what we can see. Think about the properties you can observe, measure and record.
- Sub-microscopic – smaller than we can see. Think about the particle or atomic level.
- Symbolic – representations. Think about how we represent chemical ideas including symbols and diagrams.
For learners to gain a deeper awareness of a topic, they need to understand it at all three levels.
When introducing a topic, don’t introduce all three levels of thinking at once. This will overload working memory. Instead complete the triangle over a series of lessons, beginning with the macroscopic level and then introducing other levels, in turn, once secure.
The levels are interrelated. For example, learners need visual representation of the sub-microscopic in order to develop mental models of the particle or atomic level.
Further reading
Read more about how to use Johnstone’s triangle in your teaching with these articles:
- Develop deeper understanding with models
- Improve students’ understanding with Johnstone’s triangle
- Practical ideas for using Johnstone’s triangle.
Norman Reid’s book The Johnstone triangle: the key to understanding chemistry provides a more in-depth overview, the first chapter is available to read online.
Scaffolding
Share the structure of the triangle with learners prior to use. Tell them why you are using it and how it will help them to develop their understanding. Use an ‘I try, we try, you try’ approach when introducing Johnstone’s triangle for the first time.
More resources
To further develop learner’s thinking on this topic in all areas of Johnstone’s triangle, try our Developing understanding of reacting ratios (gas volumes) worksheet.
Downloads
Decomposition of calcium carbonate Johnstone's triangle student sheet
Handout | PDF, Size 0.24 mbDecomposition of calcium carbonate Johnstone's triangle teacher notes
Handout | PDF, Size 0.26 mbDecomposition of calcium carbonate Johnstone's triangle student sheet
Editable handout | Word, Size 0.56 mbDecomposition of calcium carbonate Johnstone's triangle teacher notes
Editable handout | Word, Size 0.55 mb
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