7: Density Rainbow
For each group of 3
3 Student Activity Sheets for Learning Experience 7 (Please see PDF
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
Water (preferably warm)
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
Jar 4 – Water, 3 tblsp. salt, 3 drops of red food coloring
water will help dissolve the salt much faster in the jars. Shake the jars to
dissolve the salt.
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.
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?
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.
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
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.
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
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
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)