Density of Liquids

Patricia Doyle                 Peck School
                               3826 West 58th Street
                               Chicago, Illinois 60629
                               (312) 535-2450

Objectives:

1.  Students will discover liquids have different densities.
2.  Students will learn that the temperature of water affects its density.
3.  Students will develop a definition for density of liquids.

Materials:

For each group of 4-6 students:

balance                                        cooking oil
3 identical clear plastic glasses              water
1/4 cup measuring cup or graduated cylinder      corn syrup
stirring rod or stick                          2 one pint jars
food coloring                                  2 small aspirin bottles
paper towels                                   lab sheets for each student
felt tip markers or crayons                    green liquid soap and alcohol

Strategy:

1.  Using green liquid soap and alcohol, have the students measure 1/4 cup or 
    60 mL of each liquid and pour it into two separate plastic glasses. 

2.  Have students identify properties of these liquids.  Do both liquids take up
    the same amount of space?  Do they have the same mass (weight)?  How can we
    find out?  Have the students lift and feel.  Next have them use the balance 
    to determine the mass of each liquid.  Record the mass on the board and the
    students will notice that the soap has more mass than the alcohol. 

3.  Introduce a new term density.  When one liquid has more mass than another 
    and takes up the same amount of space, we say it has a greater density. 

4.  Next, have the students observe as you slowly pour the alcohol into the 
    glass with the soap.  Did the soap and alcohol mix?  Why or why not?  The 
    soap and alcohol take up the same amount of space but the soap has more 
    mass.  When we pour the alcohol into the glass of soap, the children observe 
    that the alcohol does not mix; it floats on top of the soap. 

5.  Set up stations for groups of 4-6 students.  Using lab worksheet, each 
    student will determine the density of water, corn syrup and cooking oil. 
    Students will weigh and record the mass of 60mL of each liquid.  Next they 
    will add 3 drops of food coloring to the glass of water and stir.  Then they
    will pour the water slowly into the glass of oil.  Does the oil and water 
    mix?  Which is denser?  Finally, they will carefully pour the syrup slowly 
    down the side of the glass containing the water and oil; set the glass flat 
    and observe which liquid is the densest. 

6.  To demonstrate that the temperature of water will affect its density, have 
    the students fill a small bottle nearly full with hot colored water.  
    Holding their finger over the mouth of the bottle have them slowly lower the 
    bottle into a larger jar of cold water.  When the students slowly remove 
    their fingers from the bottle, they will observe that the colored hot water 
    floats.  Reversing the experiment and putting the cold colored water in the 
    small bottle and the hot water in the larger jar will show that cold water 
    is heavier (denser) than hot water.  As the water temperature evens, the 
    water mixes.  Do hot and cold water have the same density?  If not, which 
    is denser? 

Evaluation:

Have the students draw pictures and label what they observed in each of the
experiments.  

Extension Activity:

Find some small objects, for example, marbles, plastic pieces, paper clips, 
styrofoam, aluminum and wood.  Have the students predict on which layer each 
object will float and then drop each object into the glass of layered corn 
syrup, water and oil.  Observe what happens.