The density of a liquid is determined by the liquid's mass per unit volume. When you compare the floating ability of different liquids (e.g., oil, molasses) you will find that a liquid's density determines its ability to float. This experiment will help your students determine the floating ability of different types of liquids.
Measure and Color Liquids
Divide your students into teams. Give each team seven 9-ounce cups with a red circle drawn around each cup to show 8 ounces. Have the teams fill each cup up to the red line with a different liquid: honey, Karo syrup, dish soap, water, vegetable oil, rubbing alcohol or lamp oil. The teams can then add four drops of a different tint of food color to each of the liquids except the honey, vegetable oil and lamp oil. The food coloring can be gently mixed with plastic stirrers.
Add Layer One to the Graduated Cylinder
Give each team a graduated plastic cylinder with measurements written on the side. Ask your students to first slowly pour the cup of honey into the center of their team's graduated plastic cylinder. The liquid should not touch the sides of the cylinder as they pour.
Add Additional Layers
Have the students very slowly pour each of the other liquids into their graduated container in the following order: Karo syrup, dish soap, water, vegetable oil, rubbing alcohol and lamp oil. The liquids may mix a little as they are pouring but will even out because of the different densities.
Result of Floating Liquids Project
As the teams pour the liquids, they will find that the seven liquids will form layers that lay one on top of another. The liquids will not separate and the layers will not move. Give each team a worksheet to study with a table showing the density of each of the liquids. The density of honey is 1.42 grams per cubic centimeter; Karo syrup, 1.33 g/cm3; dish soap,1.06 g/cm3; water, 1.00 g/cm3; vegetable oil, .92 g/cm3; rubbing alcohol, .79 g/cm3; and lamp oil, .80 g/cm3. Then ask them why they think each liquid in the graduated cylinder stays in a separate layer instead of mixing with the other liquids.
Why it Works
Why does it work? Some liquids are lighter than others because they are less dense. The liquids with the lower densities in the graduated plastic cylinder will float on top of the liquids with the higher densities. The order of the floating liquids from bottom to top will be: honey, Karo syrup, dish soap, water, vegetable oil, rubbing alcohol or lamp oil. Because rubbing alcohol has the lowest density, it should float on top, but sometimes lamp oil is the top layer. It is believed that this is because the density of the two liquids are nearly the same.
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