This is the third Investigation of the LabLearner CELL Exploring Density. In it, students explored the density of water and the density-related concept of floating and sinking.

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A. Begin the analysis of the experiments by reviewing several of the concepts introduced thus far. The following questions can be used to prompt a discussion of these concepts. Direct students to refer to each Trial as necessary.

1. Ask students: What questions were we answering during the Lab? Students were asked the following questions.  “Will ice float in oil?” “How does the density of a solid affect floating and sinking?”  “Can different states of matter have different densities?”

2. Ask students: How did we answer the questions? Can you summarize or describe what we did to answer the questions? 

• Students should suggest that to answer the first question, they observed an ice cube floating in oil.  
• To answer the second question, they predicted whether objects would float or sink and then tested the objects.  
• To answer the third question, they used the density of the object to help predict if the objects would float or sink.  They again tested the objects in water.  
• To answer the fourth question they observed how the ice cube melted in the oil and the water sank to the bottom.

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B. Continue to review the Lab experiments.  Students should refer to their Student Data Record during the review.  

Ask students the following questions to prompt discussion about Trial 2.

1. Ask students: Look at Problem 6 in your Student Data Record.  What properties of the objects helped you make predictions about which objects would float and which would sink? Student answers may vary.  Students should indicate properties such as size, shape, or weight.

2. Ask students: Were your predictions about which objects float and sink correct? Student answers may vary.

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C. Continue reviewing the lab by asking the following questions about Trial 3.

1. Direct students to Problem 11 in their Student Data Record. Ask students to complete the problem to represent substances that are more dense and less dense than water. Students should fill in the circles with particles as they did in the PreLab activity.  Remind students that More Dense means there are more particles in the space, and Less Dense means there are less particles in the space.

2. Refer students to compare the columns in their chart in Problem 7 in their Student Data Record. 

Ask students: What happened to objects that were more dense than water? Students should indicate that the more dense objects sank.

3. Ask students: What happened to objects that were less dense than water? What happened to objects that were more dense than water? Students should indicate that the less dense objects floated and the more dense objects sank. 

Students should record their answers in Problem 12 and 13 in their Student Data Record.

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Cognitive Tool: Conclusion

Explain: to students that you would like them to think about what they have discussed so far.  Based on that knowledge, they should complete Problem 14 in their Student Data  Record. 

Tell students: Based on the information we have collected about the density of objects and the density of water, we can make conclusions about density.  Fill in the blanks with more or less. 

4. Help students to apply the conclusions we have made about density to the objects from Trial 2. 

Ask students: Which objects are more dense than water, and which objects are less dense than water?  Mark the correct column in the table. Students should indicate if the objects are more or less dense than water.

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D. Review what happened to the ice and water in oil use from Trials 1 and 4.

1. Ask students: Did the ice cube float or sink in the oil? Students should indicate the ice cube floated in oil.

2. Ask students: As the ice cube melted, did the water float or sink in the oil? Students should indicate the water sank in the oil.

Tell students: Based on the information we have from the other Trials we can make a conclusion about the density of water and oil. 

Direct students to Problem 18, where they  will add the mathematical symbols for greater than (>) and less than (<), to indicate the relative density of three substances: oil, water, and ice.  

Ask students: The ice cube floats in oil. Is the ice cube more or less dense than the oil?  Students should indicate ice is less dense than oil. 

Ask students: The  water sinks in oil.  Is the water more or less dense than the oil?  Students should indicate water is more dense than oil. 

Tell students: to fill in the blanks to compare the densities of ice, oil, and water. 

3. Ask students: Can different states of matter have different densities?  How do you know? Yes. Students should indicate different states of matter can have different densities because ice and water have different densities.

4. Ask students: What do you think happened to the ice and water to make the water more dense than ice? Did the number of particles in the water change? Student answers may vary. 

Guide students: to realize that the number of particles did not change. Therefore, in order for the substance to increase in density, the same number of particles must be found in less volume than the ice.

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E. Conclude the investigation by posing the questions that follow about density.  Encourage students to think about these questions before they begin Investigation Four.

1. Ask students: Does a wood block or a brass fastener have greater density? Student answers may vary.

2. Ask students: Does the weight of an object affect its density? Remind students they will be exploring this question in the next Investigation.