Layering Liquids

Shannon Hammer, St. Charles Borromeo K-8, Minneapolis, MN, based on an original activity from Macmillan/McGraw-Hill Science, Earth's Oceans Uni, 4th grade, pg. 16-17, copyright 1993.
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Summary

In this activity, students will layer four differently colored liquids each with different levels of salinity (changing the density of the liquid) in a clear straw. Students will discuss why the liquids layered in the order they did. This can be tied in with a chemistry unit or an ocean unit.

Learning Goals

Follow a series of steps correctly. Reinforcement of accurate measurement skills and the effects that it can have on the results of the activity. Understand how the salinity of the water affects the density of the water. Vocabulary terms are salinity, density, and mixture. Correctly answer follow-up questions.

Context for Use

This activity can be used to teach concepts of how different densities of liquids can be layered and/or how the salinity of water affects the movement of ocean water. Prior knowledge of concepts is not necessary, however, measurement skills--using a ruler, teaspoons, etc. is helpful. This activity can be used as an introductory activity to a unit/concept or as a concluding activity to "prove" concepts taught. Plan 40-60 minutes for this activity. Materials needed are easily obtained. The greatest challenge of this activity is the coordination of putting your finger over the end of the straw at the correct time so the liquid already in the straw doesn't fall into next liquid to be drawn up into the straw.

Description and Teaching Materials

Groups of 2-4 Time: 40-60 minutes

Materials Needed:

NEWSPAPER to cover work surface
MEASURING TAPE or RULER to measure cm increments on straw
CLEAR DRINKING STRAWS (one per person or group)
PERMANENT MARKER to mark increments on straw
CLEAR PLASTIC CUPS (6-8 ounce, 5 cups per group)
PLASTIC SPOONS (teaspoon sized)
SALT
FOOD COLORING (RED,YELLOW, BLUE)

Procedure:

1. Cover your work area with newspaper.
2. From the bottom of the straw, using a ruler or tape measure, mark the straw every centimeter for 4 cm.
3. Fill four cups 1/2 full of water.
4. Add several drops of yellow food coloring and 1 spoonful of salt to one of the cups of water.
5. Add several drops of red food coloring and 2 spoonfuls of salt to another cup of water.
6. Add several drops of blue food coloring and 3 spoonfuls of salt to the third cup.
7. Stir each cup of colored salt water until the salt dissolves.
8. Take the straw and gently place the bottom of the straw 1 cm below the surface of the blue liquid. Seal the top with your finger. Lift the straw out of the cup.
9. Keep your finger on top of the straw and place the bottom of the straw 2 cm down in the clear liquid. Quickly lift your finger of the straw and then put your finger back on the top of the straw. The clear water should have come up into the straw with the blue water.
10. Keeping your finger on the top of the straw, lift the straw out of the water.
11. Observe the water in your straw. Write down or draw your observations.
12. Put the liquid in the 5th empty cup by releasing your finger from the top of the straw.
13. Continue experimenting with the other liquids in any order. Write down your observations with each combination of liquids.
14. Use the data collected in your observations to layer all four liquids.

Follow-up:

Discuss observations. Teach terms density / salinity.

Reference: Earth's Oceans, Macmillan/McGraw-Hill School Publishing Company, 1993, pg. 16-17

Teaching Notes and Tips

Have students practice putting and keeping liquid in a straw.
This activity is different in the instruction. Steps have been broken down more specifically that from the original source.

Assessment

Answer the following questions on paper to be handed in.

1. What two things happened when you put two different liquids in the straw?
2. How did you arrange the colors of the liquids from the bottom of the straw to the top of the straw?
3. Why do some of the liquid combinations mix in the straw while others form layers?
4. Which is heavier or more dense, equal amounts of fresh or salt water? Why?
5. How did the different amount of salt change the properties of the salt water?
6. In how many different orders can you arrange the liquids so that layers form?

Standards

3,4,5.I.B.Scientific Inquiry

References and Resources