Learning Experience 7: Density Rainbow

TEACHER’S GUIDE

Materials:

For each group of 3 students:

3 Student Activity Sheets for Learning Experience 7 (Please see PDF)

1 pipette

1 clear plastic straw

1 pieces of clay (size of large marble)

Access to the 4 colored liquids

For the class:

4 - 8.5 oz. clear plastic jars with yellow caps

Canning salt

Food coloring

Water (preferably warm)

Preparation:

Read background information. Prepare the 4 – 8.5 oz. jars with water, canning salt and food coloring in the following manner:

Jar 1 – Water with 3 drops of blue food coloring

Jar 2 – Water, 1 tblsp. salt, 3 drops of green food coloring

Jar 3 – Water, 2 tblsp. salt, 3 drops of yellow food coloring

Jar 4 – Water, 3 tblsp. salt, 3 drops of red food coloring

*Note – Warm water will help dissolve the salt much faster in the jars. Shake the jars to dissolve the salt.

Evaluation Strategy:

Students will demonstrate their understanding of the density of liquids by layering the liquids in serial order, from most dense to least dense. Students will do this by trial and error, emptying the straw and starting over until the correct order is shown.

Vocabulary:

Serial order

Objective: Students will layer four colored liquids in a straw and make decisions about the order based on the behavior of the liquid and the densities.

Can we layer liquids with different densities in serial order?

Session 1

With increasing confidence students are able to demonstrate their understanding of density. In this Learning Experience, 4 colored liquids of various slat solutions are placed around the room. Students will push a clear straw at an angle into a clay base. They will slowly layer the different colored liquids (5 to 10 drops of each color) into the straw. Students should know that the liquids must go into the straw in a certain order for distinct layers to be seen. They should record their results on the activity sheet for Learning Experience 7 in the Density Student Activity Book. (Please see PDF) If colors seem to mix, then students should try a different order until 4 distinct layers are seen in the straw.

Demonstration of Experimental Procedure:

Put a clear straw in a clay base at a 45-degree angle. Tell the students that it has to be at angle so that the liquid will run down the side of the straw.

Demonstrate how to use the pipettes. Show the students how to put the liquid in to the straw, slowly so that it runs run the side of the inside of the straw. One drop at a time maybe to difficult for them, but emphasize that it should not just be squirted in.

Show students how much of each liquid to put in the straw – 5 to 10 drops (emphasize that it does not have to be the same amount each time, but it should be similar. Tell them that they will need to be able to fit the 4 different liquids into one straw.

Now demonstrate how to put more than one liquid into the straw. Ask the students what they think will happen if they put more than one liquid in the straw. First add some of the blue solution, and then add the red. They should form layers. Ask the students why the two solutions didn’t mix. Make sure they understand that the liquid on bottom has a higher density than the liquid on top. Then ask the students what would happen if you put the red liquid in first, and then added the blue one, and why? Do the demonstration so they can see what happens. (The denser blue solution will sink underneath the red one.)

Draw a column on the board, similar to the one in the Density Student Activity Book. Show the students how to record each step they do in the experiment. Start with the first liquid added to the straw – write the first letter of its color in the space provided (Y = yellow, R = red, B = blue, G = green). Repeat with the other liquids in the order they are added.

Discussion Questions:

Why do you think we are able to layer the liquids? The 4 liquids must have different densities. What do you think the four liquids could be?

After students have successfully layered the 4 liquids, tell them that the liquids consisted of plain water and salt solutions. How much salt would we have to add to the water to get the layered results? Students should say different amounts of slat in each liquid would account for the result.

What can we say about the 4 liquids in terms of density?

Could we determine the density of each colored liquid? How?

As an extension activity – the class can mix together their own salt solutions and calculate their densities.

For the accompanying Density Science Student Activity Book, please refer to the PDF found here. (Please see PDF)

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