MnSTEP Teaching Activity Collection > MnSTEP Activities > Density Differences

Density Differences

Mary Holmberg
Eden Valley-Watkins Elementary School
Eden Valley, MN

Based upon an original activity from Houghton Mifflin, DiscoveryWorks, p. E52
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Summary

In this chemistry lab, students investigate differences in ocean water density. Students record density data from salt, ice, and hot water samples in their notebooks. Students then simulate ocean water temperature levels in a graduated cylinder, extending density knowledge by introducing oil as a pollutant.

Learning Goals

*Learning Goals
1. The student will use the process of inquiry to determine density differences
2. The student will use data analysis to predict the levels of liquid based upon density
3. The student will synthesize information and develop a model including new insights
*Key Concepts
1. Cold water is less dense than warm water and salt water
2. Warm water is less dense than salt water and denser than cold water
3. Oil is less dense than water, therefore when an oil spill occurs, oil floats on top of water
*Vocabulary Words
1. density
2. salinity
3. temperature

Context for Use

Grade level: Sixth
Class size: 25-30
Activity: Lab
Time allotted: Two 45-minute class periods

Special equipment: Large group: one clear tub filled with six cups of ice water, one clear tub filled with six cups of hot water, one clear tub filled with six cups of saturated salt water, one thermometer per tub. Density straw for each tub: cut a straw in half. Using a black fin-tip marker, mark lines every cm from the bottom of the straw to the top. Roll a piece of clay into a cylinder. Insert the clay roll into two cm of the bottom of the straw. Small group equipment: 1/2_ c. hot water, 1/2_ c. ice water, 1/2_ c. salt water, 1/2_ c. cooking oil, one graduated cylinder, three different food colors.

Skills or concepts previously mastered:
1) ocean water contains salt
2) ocean temperatures vary at different depths

Curriculum Situation: 2000 Houghton/Mifflin Discovery Works! 6th grade Oceanography Unit: Differences in Density and Pollution! Oil Spill!
*Easily adaptable in other settings studying water temperature, salinity, and density.

Subject: Geoscience, :Oceanography, Chemistry:General Chemistry:Properties of Matter, Chemistry, Environmental Science:Waste:Toxic and Hazardous Wastes, Environmental Science:Waste, Environmental Science,
Resource Type: Activities:Classroom Activity
Grade Level: Middle (6-8)

Description and Teaching Materials

Materials: Large group: one clear tub filled with six cups of ice water, one clear tub filled with six cups of hot water, one clear tub filled with six cups of saturated salt water, one thermometer per tub. Density straw for each tub: cut a straw in half. Using a black fin-tip marker, mark lines every cm from the bottom of the straw to the top. Roll a piece of clay into a cylinder. Insert the clay roll into two cm of the bottom of the straw. Small group equipment: _ c. hot water, _ c. ice water, _ c. salt water, _ c. cooking oil, one graduated cylinder, three different food colors.

Based upon prior knowledge, students will be asked to describe ocean water using the "Five Es": Engage, Explore, Explain, Expand, and Evaluate. Students will determine the differences in density of three samples of water: ice, hot, and salt saturated. Students will create a chart in their journal including the following: water type, water temperature, amount of straw beneath the surface (cm).

Procedure

Small group:
Students rotate through ice, hot, and salt water stations, inserting the clay straw into the tub of water. Students record the centimeters of straw beneath the surface, as well as the temperature of the water in their journal charts. Students will determine density levels of the water based upon the amount of straw beneath the surface, recording findings in their journals.

Large group:
The teacher leads the group to discuss conclusions. Which water is the densest? Why? Which was the least dense? Why? Students draw and label a density continuum picture in their journals with the least dense water on the top, most dense on the bottom. How does this activity relate to ocean water? What if an oil spill occurred in the ocean? Students predict where the oil would be on the density continuum with a written explanation

Small group:
Carefully pour _ cup blue dyed ice water into a graduated cylinder. Students record predictions of the addition of red-dyed hot water: will the water sink beneath the ice water or float on top? Why? Carefully add _ cup hot water. Record results in pictures and words. Predict blue salt water addition. Pour _ cup salt water into the cylinder. Record results. Predict addition of oil. Carefully pour _ cup of oil into the cylinder. Record results. Synthesize thoughts into effects of oil spills, based upon density differences.

This activity is an extension/closure activity for the density differences chapter. The activity serves as the introduction activity for the pollution chapter in the 2000 Houghton/Mifflin Discovery Works! 6th grade Oceanography Unit.

Teaching Notes and Tips

1) prepare hot water and ice water in advance
2) plug end of straws with extra clay to prevent leaks
3) This activity is different from what I've done in the past in that students use a graduated cylinder to display density differences. Students also predict and determine what will happen to oil placed in the water.

Assessment

1) Journal entry chart includes: title, water type, water temperatures, centimeters beneath the water (10 points)
2) Students correctly display density differences in the density continuum in journal entries. (4 points)
3) Explanation of density differences on the continuum are accurate (4 points.)

Standards

6.2.1.1.1 Explain density
6.1.2.2.1 Engineering design to solve a specific problem

References and Resources

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