Part 3: Using Color to See How Liquids Combine

Can you tell a difference between liquids by the way they look when they combine with water?

In this and the following activity, you will use a different method to observe another characteristic property of water, salt water, alcohol, and detergent solution. The liquids will be colored yellow so that you can observe the different ways they combine with water that has been colored blue. After carefully observing the combining liquids in this activity, you will be able to identify these same yellow liquids, labeled A, B, C, and D;Using the combining test to identify the unknown liquids.

View a past student sample of Physical Properties of Liquids.

Materials needed for each group

• • Tap water

  • Isopropyl rubbing alcohol (70%)

  • Detergent

  • Salt

  • 5 Droppers (4 labeled droppers from the previous activities + 1 additional)

  • 5 Small cups (4 labeled cups from the previous activities + 1 additional)

  • Crayons or colored pencils

  • Toothpicks

  • Paper towels

  • Laminated lab test sheet

  • Yellow food coloring

  • Blue food coloring

  • Safety goggles

Notes about the materials

• • Be sure you and the students wear properly fitting goggles.

  • Procedure

    1. Add drops of each liquid to its labeled circle to completely fill each circle on the chart. Depending on your dropper, you may need to add about 5 drops or more.

    2. Then, use a toothpick to pull the blue water toward the yellow water. It may take a few tries to get them to join. Instead of holding the toothpick straight up and down, it is helpful to hold it more horizontally so more of the toothpick touches the blue water. As soon as the two drops meet, lift the toothpick away and discard it. Watch the two drops combine on their own. Do not stir.

    3. Record observations and make a labeled diagram in the proper box of the Physical Properties of Liquids assignment sheet.

    4. When the drawings and captions are complete for the first pair of liquids, combine the second pair and record your observations.

    5. Continue testing the remaining pairs in this manner.

  • Part 4: Using the combining test to identify the unknown liquids

  • How can you use the characteristic way each liquid combines with water to identify the unknown liquids?

  • In this investigation, you have seen that liquids absorb into different surfaces and combine with water in characteristic ways. As a culminating challenge, you will use your recorded observations from Part 3 as you test four unknowns and try to identify them. The characteristic way each of the household liquids combines with water will allow you to correctly identify these same liquids, relabeled A, B, C, and D.

  • View a past student sample of Physical Properties of Liquids.

  • Materials needed for each group

• • • Colored solutions from Part 3: Using color to see how liquids combine (4 yellow + 1 blue)

    • Tap water

    • Isopropyl rubbing alcohol (70%)

    • Detergent

    • Salt

    • 5 Droppers (labeled from Part 3)

    • Additional small cups

    • Crayons or colored pencils

    • Laminated lab test sheet

    • Toothpicks

    • Paper towels

    • Yellow food coloring

    • Safety goggles

• • Notes about the materials

• • • Be sure you and the students wear properly fitting goggles.

• • Procedure

• • 1. Use drops of yellow liquid labeled A to fill its circle and then fill the opposite circle with blue water. Combine this pair with a toothpick the way you did in the last activity.

    2. Record observations and make a labeled diagram in the proper box of the Physical Properties of Liquids assignment sheet.

    3. Repeat Steps 1–2 for each of the remaining unknowns.

    4. Record the identity of each unknown liquid (A, B, C and D) on your activity sheet and include evidence to support your claims.

• • Physical Properties of Liquids Part 1

  • Physical Properties of Liquids Part 2

From Inquiry In Action