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Investigation Question 2:
How can you separate a soil mixture?
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What To Do
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Setting the
Scene
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©
Lynn Betts, NRCS |
Three soil profiles show the differences in slightly eroded versus severely eroded soils in central Iowa. |
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Ask students to look at the picture of the soil samples above. Ask the students: Do all of these types of soil look alike? In what ways are they the same? Different? How could you separate the different parts of the soil mixture?
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Presenting the Investigation
Question
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After the scene is set, introduce your students to the investigation question: “How can you separate a soil mixture?”
Tell your students that they will be investigating this question and that at the end of their investigations, they will be able to provide reliable answers.
Have your students brainstorm ideas about how this investigation question could be investigated.
- Design an experiment that could be used to test the investigation question.
- What materials would be needed?
- What would you have to do?
- What would be measured?
- How long would the experiment take?
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Assessing What Your Students Already Know
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Your students should be familiar with many types of mixtures, but may not have thought of different ways of separating these except for picking them apart manually (as people do with snack mixes or mixed nuts). They may need your help in coming up with ways of separating their soil mixture.
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Exploring the Concept
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- Give each student group a set of the materials. Ask the groups to come up with a plan for how they can separate their soil mixtures using the tools you have provided. [Some plans they might think of can be: picking apart the soil with forceps; shaking the soil between two tumblers; putting the soil into a tumbler of water or pouring the soil through air.]
- Ask student groups to share their plans. Make a list of these plans on the board. Ask students to comment on the plans – which do they think will do the best job of separating the soil mixture and why? When you finish the discussion, ask students to try out their plans. Remind everyone to put on safety goggles first.
- Circulate around the groups, helping those who are struggling. Remind students to record their observations as they try to separate the soil sample.
- When everyone finishes, ask students to share their results. If your classroom setting allows it, you might want to take the class from group to group to “visit” students as they demonstrate their soil separation methods and explain what they did and why.
- Remind students to wash their hands at the end of the investigations.
When everyone has shared his or her results, ask the class: What method seemed to work the best to separate the soil? [Pouring soil into water will result in different layers. More dense particles sink to the bottom, while less dense particles end up on the top.] Which method took the least work? Why was that? [Pouring into water is less work than picking the soil mixture apart by hand. Pouring through air and shaking the sample up really doesn’t separate the particles much.]
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