- Show pupils some examples of different limestone,
eg brown limestone; ask them to describe some differences between them,
eg appearance, porosity. Explain that they are going to find a way of investigating differences in composition.
- Establish that limestones are carbonate-rich rocks, but may contain other components. Remind pupils of how carbonates react with acids and help them to plan a way of comparing the carbonate content of two samples,
eg by weighing samples before and after reacting with acid, measuring the volume of acid required to completely react with the carbonate. Ask pupils to think about what they are planning to do and perhaps try out some ideas. Ask groups of pupils to explain and evaluate their methods and what they found out,
eg using a flip chart or overhead projector (OHP). Where appropriate, extend the work by providing pupils with data about the carbonate content of different limestones and information about how they were formed, e
g accumulation of fossil fragments, by chemical precipitation, and why,
eg mud-free lagoon, reef. Ask pupils to use the data to make generalisations about composition and formation.
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- describe some observable differences between limestones
- suggest an approach to the problem and try it out, identifying difficulties,
eg you have to dry the limestone before you weigh it again, it's better if you crush it up so that the acid reaches all of it
- describe and evaluate their approaches indicating problems they encounter
- generalise that rocks are mixtures and vary in composition
- relate the composition of limestone to the process of formation
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