DENSITY

Rebecca Andresen

Gannon Dooley

Timothy Francis

__ Student Misconceptions Addressed by the Lesson__:

Objects with nearly the same mass will behave the same. All solids sink. All liquids mix.

__ Lesson Goal__: Students will investigate the property of density as a unique physical property of an element or compound.

__ Grade Level__: Grades 6-9

__ Prerequisites__: Students are familiar with proper lab use of the triple beam balance. Students should have a working knowledge of the formula for volume and how volume is measured for solids and liquids.

__ Content Accommodations: NSEA Standards__: Content standard B, page 149 and page 176.

__ Safety Accommodations__: Students should not taste any of the liquids or food products used in this activity. While students are working with glass graduated cylinders, students should practice safe lab techniques.

Exploration - Begin Lesson

__ __

__Objectives:__

The student will review the concept of heavy versus light and the concept of sinking versus floating.

The student will conclude that solid objects of the same size and shape can have different weights and therefore different densities.

Materials: (for each group)

Various objects such as coins, rocks, rubber stoppers, pieces of wood, etc.

Triple beam balances, bucket of room temperature water, two unopened soft drink cans (one diet and one regular).

Procedure:

A. 1. Have the students work in groups to test various objects on a balance to determine heavier and lighter objects.

2. Have students test to see whether the objects sink or float in water. Record results in a table labeled in the following way.

*object mass sink or float*

____________________ ___________ ____________

____________________ ___________ ____________

____________________ ___________ ____________

3. Ask, Does size determine whether or not an object will sink or float?" Have the students write their responses in their science journals.

B. 1. Have students use a balance to find the mass of a can of regular soft drink and the diet version of that soft drink. Next, have the students record the volume of the soft drink can in mL.

2. Students will place both soft drink cans in a bucket of water and make observations. Record observations.

3. Ask the students, "What reason do you give for the results of your experiment?"

C. 1. Introduce the term density and the formula D = *m* / V.

2. Have the students calculate the density of each of the soft drink cans and record the results. Give the students the information that water has a density of 1.00 g/mL.

3. Have the students answer the following questions:

Which can has the greater mass? Which can sinks and which one floats? Which can has the greater density? Compare the densities of the regular soft drink and water and the diet soft drink and water.

Background Knowledge

The can of diet soda should float and the regular soda should sink. The regular soda has ten more tablespoons of sugar added to it thus it has more mass than the diet soda. Although the density of the soda in either can is greater than that of water, the CO2 gas trapped above the liquid also provides buoyancy.

Density differences are used to separate ripe tomatoes from green tomatoes and coal and shale. Students can demonstrate this by placing green and red tomatoes into an aquarium. This will simulate the separation similar to that done when machine-picked tomatoes are separated to make catsup.

__Evaluation: __ Each group of students will have completed data sheets for the exploration activities. Students should have recorded predictions, results, and conclusions in their lab notebooks. The journal entry should be kept on hand for later use in the lesson cycle. Observation and monitoring should be used throughout the laboratory experience.

Invention - Continue Lesson

__Objectives__:

The student will develop and utilize skills in observing, predicting and testing. The students will apply the concept of density as it relates to solids, liquids, and gases.

Materials:

grapes, corn syrup, corn oil, water, food coloring, glycerol, paperclips, corks, pieces of a candle, plastic cups (6 oz.), Density Results Sheet, medicine droppers, graduated cylinders.

__Procedure__:

A. 1. Distribute to each of the groups: corn syrup, corn oil, water, and glycerol (4oz. of each in plastic cups).

4 medicine droppers, 10 plastic cups, 1 paperclip, 1 cork, 1 candle piece, 1 grape and a Density Results Sheet.

B. 1. Explain to the students that they are now going to hypothesize and experiment with the densities of the liquids. The students weigh each of the four liquids and make hypotheses on the ranking of the liquids from least dense to most dense. These hypothetical rankings will be recorded on the Density Results Sheet. After making their hypotheses, students will begin layering the four colored liquids into a plastic cup one color at a time. As soon as the colors mix, students will attempt a new combination. Students will continue experimenting with different combinations until they have layered the liquids in order from most dense to least dense, recording the results. The students will pour all remaining liquid, in the proper order, into an empty plastic cup.

2. Students will then hypothesize, ranking the solids from least dense to most dense. Students will weigh their solids on a balance in order to make their hypotheses. After recording their hypotheses on the Density Results Sheet, students will drop each of the solids, one at a time, into the cup containing the layered liquids. Students will then record the actual order of the solids by density and compare the differences between their hypotheses and their actual results. They will then write a summary about what they observed.

__Evaluation__: Students will turn in data sheets with hypotheses and results. A summary explaining their observations about how their hypotheses compared to actual test results.

Density Results Activity Sheet

Hypothesize, ranking the liquids from the heaviest to the lightest in density, then write the actual ranking.

Hypothesis Actual

1. ________________________________ ________________________________

2. ________________________________ ________________________________

3. ________________________________ ________________________________

4. ________________________________ ________________________________

5. ________________________________ ________________________________

Hypothesize, ranking the solids from the heaviest to the lightest in density, then write the actual ranking.

Hypothesis Actual

1. ________________________________ ________________________________

2. ________________________________ ________________________________

3. ________________________________ ________________________________

4. ________________________________ ________________________________

5. ________________________________ ________________________________

Write a summary of your observations about your hypotheses compared to your actual test results.

Expansion - Complete Lesson

__Objectives__:

The student will learn how to determine the mass of an object.

The student will learn how to determine the volume of an object by two techniques: using the volume formula and displacement of water.

The student will learn how to determine the density of an object.

The student will use the physical property of density to identify an unknown sample.

__Materials needed__:

Two wood blocks of different sizes with rectangular or square shapes; four pennies, two pre-1981 and two post-1982; a variety of unknowns (suggestions: nails made of iron, aluminum foil, silver jewelry, etc.); a list of actual densities; graduated cylinders; rulers; calculators.

Procedure:

A. 1. Have the students find the mass and the volume of the wood blocks. Record measurements on data sheet. (Volume = length x width x height) Remember 1 cubic centimeter equals 1 milliliter.

2. Students will calculate the density of each of the blocks using the density formula.

B. 1. Find the mass of the pre-1981 penny and the volume using the displacement of water. Record your results on your data sheet.

2. Find the mass of the post-1982 penny and the volume using the displacement of water. Record your results on your data sheet.

C. 1. Find the mass and volume of unknown # 1.

2. Use the information in step 1 to calculate the density of unknown #1. Record your results.

3. Obtain a sample of unknown #2and find the mass and volume of the sample. Calculate the density of the sample. Use the list of actual densities to identify the composition of the metal.

. 4. Choose an unknown liquid and find the mass and volume of the sample. Calculate the density and identify the liquid using the chart.

__Evaluation__: Students will turn in data sheets and Analysis & Conclusion Questions. performance assessment of proper lab techniques using a observation checklist.

**Scoring Rubric**:

Demonstrate Competence:

For 5 points: The response is exemplary and complete. The formula for density is correct. The explanation contains more than one way of determining the volume of an object. Densities of unknown solids have been determined.

For 4 points: The response is correct and the explanation is clear.

For 3 points: The response is generally correct but the explanation lacks clarity.

For 2 points: The response indicates a partial solution. The explanation is incoherent.

For 0 points: The student leaves a blank page or writes " I dont know".

Analysis & Conclusion Questions

1. How does the density of the you two different sized wood blocks compare?

2. Compare the density of the two pennies? Do they have the same composition? Justify your answer. (Hint: Remember the story about the king and Archimedes when he had to find out if the crown was real gold.)

3. Compare the results of the density of the unknown #1 metal. What can you conclude about the composition of the metal? Explain.

4. Describe in a paragraph the method of determining the mass and volume of your unknown #2 metal sample. What is your sample and how certain are you about your result.

5. Describe in a paragraph the method of determining the mass and volume of your unknown liquid sample. What is your sample, and how certain are you about your result?

6. Is the density of a particular type of substance always going to have the same value?

Explain.

EXTENSION TO NASA MATERIALS:

Have students research the densities of terrestrial planets using the internet.

Possible questions:

1. What are the densities of Mercury, Venus, Earth, and Mars?

2. Hypothesize what the composition of a planets core would be if it has a density of 5 g/cm3 or greater?

3. Compare and contrast the densities of the outer and inner planets.

4. What is the density of Saturn? Would it float in a tub of water if there was one large enough to hold it?

Data Sheet

Sample Mass Volume Density

wood block #1 ________________ _______________ ____________

wood block #2 ________________ _______________ ____________

pre 1981 penny ________________ _______________ ____________

post 1982 penny ________________ _______________ ____________

unknown #1 ________________ _______________ ____________

unknown #2 ________________ _______________ ____________

unknown liquid ________________ _______________ ____________

List of Actual Densities

SOLIDS Density (g/cm3) LIQUIDS Density (g/mL)

stainless steel 8.037 corn oil 0.925

aluminum 2.699 corn syrup 1.38

calcium 1.55 glycerol 1.26

carbon 2.266 mercury 13.6

copper 8.92 water 1.00

gold 19.32

iron 7.874

lead 11.342

nickel 8.908

silver 10.49

tin 7.265