Which Is Heavier, a Kilogram of Feathers Or a Kilogram of Lead (Pb)? Explain Your Answer

Science.8 Name ______

Date ______

Essential Questions Vocabulary Objectives 1. What are the physical properties of density, mass, volume 1. Investigate physical property of density. matter? 2. Calculate density. Which is heavier, a kilogram of feathers or a kilogram of lead (Pb)? Explain your answer. ______

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If you said that a kilogram of feathers would be equal to a kilogram of lead, then you are correct! A kilogram is a kilogram whether it is of feathers or lead. A kilogram of feathers however, would take up a lot more space than a kilogram of lead. That means a kilogram of feathers has more volume than a kilogram of lead. If you had an equal volume of feathers and lead, then the mass of the two would be very different. The relationship between the mass and volume of anything is called density.

Density is a measurement of how much matter is packed into a substance.

To find the density of an object you must first measure its mass and volume.

Once you have this information, you divide the mass by the volume.

Density= M ass

Volume

Problem: Calculate the density of your samples to determine the identity of the substances.

Materials: triple-beam balance 100 mL plastic graduated cylinder

Unknown Samples (4 samples) ruler

Procedure:

1. Determine the mass of each solid using the triple beam balance. Record the mass of each sample in your data table. 2. Determine the volume of each solid using your graduated cylinder. a. Fill your graduated cylinder to 60 ml. b. Carefully lower your sample into the cylinder. c. Determine the new water level with the sample in the cylinder d. Subtract the new volume – 60 ml (the original volume) to find the volume of your sample. e. Record the volume of each sample in your data table. 3. Calculate the density of each sample. Use the formula Density=Mass/Volume. Record. 4. Use the calculated density to determine the identity of your substances. Data Table:

Sample Description Mass (g) Volume Density Identity of Substance (ml) (g/ml) (color, length, shape, etc.)

Analysis:

1. Plot the density of your substance on the class chart. Compare the density of your substances to substances of the same color from another group. What do you notice about items of the same color? What does this mean about the substances?

2. Is it possible for two substances to have a different mass, but the same density? Explain.

3. Is it possible for two substances of the same volume to have a different mass, but the same density? Explain.

4. What is the density of a solid with a volume of 12 cm3 and a mass of 60g? Show your work.

5. If an object has a mass of 75 g and volume of 3 ml, then what is its density? Show your work.

6. If an object with a density of 5 g/cm3 is cut into two equal pieces, what will the density of each piece be? Explain your answer. 7. Does the shape of an object affect its density? Explain. The density of water is 1 g/cm3 . An object will float in water if its density is less than 1 g/cm3. If the density is greater than 1 g/cm3 the object will sink. For each of the following elements calculate the missing information and determine whether the element will float or sink if placed in water.

Element Mass Volume Density Sink or Float

Aluminum 8.1 g 3 cm3

Arsenic 85.5 g 15 cm3

Helium 83.33 g 0.18 g/cm3

Gold 15 cm3 19.3 g/cm3

Neon 6 cm3 .89 g/cm3

Lithium 2.65 g 5 cm3

Chlorine 5 g 3.2 g/cm3

Uranium 190 g 10 cm3

Potassium 25 cm3 .86 g/cm3

Conclusion:

1. Why is density an important physical property?

2. Summarize what you learned. Write a minimum of 3 complete sentences. Teacher Notes:

Prepare a class chart for students to post calculated densities. Students should see that same color samples have the same density. Discuss with students that different size pieces can have the same density because it is the ratio of mass to volume that gives density, not just mass or volume alone.

If time allows, plot mass s. volume for samples of the same color to notice that they create a straight line. The slope of the line is the density of the sample.

Densities of Samples:

Maple 0.77

Polypropylene 0.90

Polyamide (Nylon) 1.15

Acrylic 1.17

Polyurethane 1.23

Phenolic 1.32

PVC 1.37

Teflon 2.2

Aluminum 2.71