Students compare the dissolving of salt and sugar and then conduct a dissolving test on unknown substances marked A, B, and C to investigate the question: Can substances be identified by how well they dissolve in water?
Objective
Students will be able to plan and carry out an investigation to compare the solubility of different substances, and develop and explain a particle-level model to describe the process of dissolving. Students will also be able to explain that substances dissolve by different amounts because of the molecules they are made from.
Key Concepts
- For a dissolving test to be fair, the same amount of each substance being tested, and the same amount of water need to be used.
- The amount of a substance that dissolves in a certain amount of water is a characteristic property of that substance.
- The different atoms and molecules of a substance give it its characteristic solubility.
NGSS Alignment
- NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.
Summary
In earlier grades, students observed and tested objects and materials, and saw that the items could be grouped based on their characteristic properties. In this and the following lessons in Chapter 2, students continue to develop this idea and see that the characteristic properties of a substance can be used to identify the substance.
In this lesson:
- Students are given labeled samples of salt and sugar. They are also given unknown samples marked A, B, and C. One is salt, one is sugar, and the other is alum, which looks like it could be either salt or sugar.
- Students first use a dissolving test to see how salt and sugar dissolve in water. Students then run the same dissolving test on substances A, B, and C; identify the salt and sugar; and conclude that the other substance must be something different.
- Students then see an animation to help explain that the substances are made of different atoms and molecules, so they dissolve differently.
Evaluation
Download the student activity sheet and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.
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