Bruno 1
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Milk Rainbow
Teacher Instructions (best for 3rd-6th grade students)
This experiment deals with surface tension, polarity (also discussed
as like dissolving like), chemical bonding, and nutritional content. Once
student are introduced to these basic concepts through discussion,
demonstration, and modeling, they are asked to hypothesize what will
happen in regards to polarity and surface tension when dish soap and
food coloring are added to a substance.
Key Terms:
Surface tension is the increased attraction of the molecules at the surface
of a liquid resulting from forces of attraction on fewer sides of the
molecules.
Polarity is the separation of electric charge.
Chemical bonding is caused by the attraction of opposing charges.
Hydrophobic is the characteristic of not combining with or dissolving in
water. Oils are examples of such “water fearing” substances.
Hydrophilic is the characteristic of readily absorbing or dissolving in water.
Glucose is an example of a “water loving” substance.
Instructions:
1) Discuss the concept of the activity.
 Have the children brainstorm about the contents of whole milk.
 Discuss the key concepts of surface tension, polarity, and
chemical bonding pertaining to the elements of milk.
 Encourage the use of the knowledge they have gained by
facilitating a class brainstorming session about what would
happen if a substance like soap was added to milk.
2) Do a demonstration for the class.
 Put milk in a petri dish or a shallow pan/bowl.
 Put food coloring in the center.
 Use a dropper to place a small amount of soap in the middle
of the food coloring.
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3) Have the children physically model what happened in the
demonstration.
 Using signs or party hats, label each student as either soap, food
coloring, water, or fat/protein.
 With the entire class, model what occurred at a molecular level
when the soap and food coloring were added to the milk.
4) Using the color of their safety glasses, divide the kids into groups of
four.
 Give each student a worksheet.
 Give each group 6 petri dishes or shallow bowls, two droppers,
food coloring, crayons, dish soap, and the six substances that
they will test.
5) Have them complete the activity using whole milk.
 Tell them to draw what they observe in the appropriate circle on
their worksheets.
6) Have them complete the activity using water.
 Once again, have them draw their observations in the
appropriate circle.
 Compare and contrast the outcomes when using water and
milk.
7) Repeat step 6 using glue and shampoo.
8) Compare and contrast the different outcomes, and brainstorm the
cause of the observed differences.
9) Present apple juice and a clear soda as mystery items, and have
the students complete the activity with these mystery items.
10)The students should use the outcome of the activity with the mystery
items to analyze characteristics of the liquids.
11) As a final element, mention the nutritional content of these liquids.
12)For clean up, everything is safe to pour down the drain.
Further experiments/discussion:
Take a more in-depth approach to nutrition. Discuss what it means for
something to be hydrophobic and/or hydrophilic and the significance of
these properties to this experiment. Have the kids bring in additional items
for this activity.
Total time: 40 mins
Materials (estimated for a class of ~24 students):
37 petri dishes or shallow containers
3 sets of food coloring
12 droppers
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1/28/10
Dish Soap
Whole Milk
Glue (such as Elmer’s)
Water
Clear Shampoo
Apple Juice
Clear Soda (ex. Sierra Mist)
Crayons
1 box of small cups (to hold the substances being tested)
Note: All of the materials needed for this experiment can be
purchased at any general store.
References:
http://www.stevespanglerscience.com/experiment/00000066
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Key Terms
Surface tension is the increased attraction of the molecules at the
surface of a liquid resulting from forces of attraction on fewer
sides of the molecules.
Polarity is the separation of electric charge.
Chemical bonding is caused by the attraction of opposing charges.
Procedure





Pour the milk into the petri dish or shallow bowl
Drop food coloring into the center of the milk
Draw dish soap into a dropper
Put one drop of dish soap into the center of the food coloring
Draw what you see when the soap touches the food coloring
and milk…
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1/28/10
Milk
 Repeat the activity substituting milk with water, clear
shampoo, and glue. Make sure you draw what you observe.
Water
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Shampoo
Glue
 Now that you know all about bonding, surface tension, and
polarity, lets see what we can learn about some mystery
liquids.
 Complete the activity with the given mystery liquids.
 Draw what you see and lets brainstorm about these liquids.
Mystery 1
Mystery 2
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 Write everything that you observed and learned about the
first mystery liquid? From these observations, what can you
say about the ingredients of the mystery liquid?
 What about the second mystery liquid?