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In this lesson students will learn that chemical changes are reversible and that, unlike a physical change, they produce a new substance.
Often students have the misconception that making a solution such as salt water produces a chemical change. It is important to discuss reversibility of a physical change and that chemical changes produce a new substance, physical changes do not. At the conclusion of this experiment, it is important for students to observe the same amount of salt is left in the bowl that was used to make the solutionno matter was destroyed. The amount of water also remains the same, but that some of the water underwent a phase change to a vapor.
It is also important to activate student prior knowledge of the Water Cycle. The Water Cycle has multiple examples of physical changes.
1. Use Science Processes and Thinking Skills
5. Understand the Nature of Science
Invitation to Learn
Ask students to imagine that while on a field trip, the class is stranded on a deserted island in the ocean. There is plenty of undrinkable salt water, but no fresh water. Explain that we have the following materials with us to make fresh drinkable water from salt water: large and small, bowl, plastic wrap, rocks, their knowledge of the Water Cycle, and the energy from the sun.
Shepard,L.A.(Nov2005). Linking formative assessment to scaffolding. Educational leadership, 63.3 p.3
To help scaffold student understanding of physical changes, this activity builds on students prior knowledge of the Water Cycle to understand physical changes. This article, Linking Formative Assessment to Scaffolding, discusses the importance of eliciting prior knowledge to help students build new understanding by making sense of new experiences in light of what they already know. Teachers should not think of prior knowledge assessment as a discrete pretest to use from time to time. Rather it should be common in classroom practice. Knowledge activation routines help develop students metacognitive abilities while providing relevant knowledge connections for specific units of study.
Marzano,R.,Pickering,D.,Pollock,J.,(2001) Classroom Instruction That Works, Alexandria, VA.ASCD
This text covers multiple research based instruction strategies that when implemented, improve student achievement. The more learners use linguistic and non-linguistic representations of knowledge, the better they are able to think and recall knowledge. One research based method that enhances the development of non linguistic representations in the classroom is making physical modelsconcrete representation of the knowledge being learned. Nothing NewA Physical Change was designed to give students the opportunity to use and create a nonlinguistic representation of a physical change. Students will create and observing a working solar still. Another strategy presented in this book was Generalization/Principle Patterns. The Physical or Chemical Change? checklist will be used to help students make generalizations when determining the types of changes occurring in matter.