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Lesson Plan: Density

Lesson title:

How can we figure out the density of an unknown substance?

Anticipatory set: Have you ever made your own salad dressing? What happens when you mix the oil and the vinegar then shake the container and set the solution down? The two liquids separate, right? Have you ever wonder why one is on top while the other is on the bottom? Well, it has to do with the densities of the liquids. Our experiment today will show you how the density of a solution determines where in a multilayer solution in sits. This multilayer is often called a gradient. Objectives: 1. The student will learn how density influence whether a liquid floats or sinks. 2. The student will be able to calculate density. 3. The student will learn how to explain the stacking observed in a known gradient using densities values. 4. The student will be able to predict where a liquid will stack among several known densities. 5. The student will be able to estimate the density of an unknown solution based on where it is located on a known gradient.

Supplies: 1. Several graduated cylinder or 2, 3 tube per group. 2. Vegetable oil 3. Isopropyl alcohol 4. Corn syrup 5. Dawn liquid 6. Water ( H20 ) 7. lab towel Procedure: (Time limit :1 to 2 day --depending on your students). Construct a Density gradient: The following household liquids vary in density from about 0.9 g/mL to about 1.4 g/ml: vegetable oil, water, corn syrup, detergent and isopropyl alcohol. 1. In this activity you will be attempting to rank them in order of increasing density. Use a mechanical pipette or eye dropper to place a small amount of one fluid onto the surface of another. To avoid turbulence, you should release the liquid from the pipet as slowly as possible. Preferably down the side of the test tube. If the fluid sinks, then it has greater density than the fluid in which it has been placed, but if it floats, it has a lesser density. 2. Repeat the procedure with other pairs of liquids until you believe you have established a density ranking.(Teacher needs to initial each liquid pair combination___).

J. Bannister, EMS. Eustis, Florida LCSB 2008

3. Record your observations by drawing a sketch of the two liquids and their position in the test tube. 4. _______ (Teacher's initial) Make sure you get your work checked before you construct a five-tier density gradient in a test tube. If your density scale is correct, there will be only minimal mixing of the liquids. 5. From the stock supply on the front desk choose one of the unknown liquids( A,B or C) 6. Label the fluids in the diagram and estimate the unknown liquid's density. 7. Record your results. Closure: Student Questions (per group/class) 1. In your own words define density? 2. Of the liquids we used today, which was the most dense? Why? 3. Which liquids were less dense? Explain? 4. How did you estimate the density of the unknown liquid? Assessment: 1. Listen to students responses to closure question prompts. 2. HWK--If you had a cylinder filled with mercury (13.6g/ml), water (1.0g/ml) and maple syrup (1.4g/ml). What position will each fluid occupy, if you constructed a density gradient? Explain using examples from our class demonstrations.

References: The Center for Applied Research in Education, 1999. Density of Liquids. Adaptation from E. R. Hutton. SCI 442, MTSU. Spring 1996

J. Bannister, EMS. Eustis, Florida LCSB 2008

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Lesson Plan: Density

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Lesson Plan: Density