Materials Included In Kit

Additional Materials Required

Teacher Tips

• Enough materials are provided in this kit for 15 groups of students. This laboratory activity can reasonably be completed in two 50-minute class periods.
• The density readings for all of the objects in Part 1 should be very close since they are all composed of aluminum.
• Use plastic cylinders to minimize breakage.
• A larger cylinder or beaker may be used if the rock samples are too large to fit into a 50- or 100-mL graduated cylinder.
• Choose rock samples of different densities for a variation of results.
• Have students try to figure out the volume of the spheres by measuring the diameter of the spheres and using the equation V = 4/3πr³.

Sample Data

Answers to Questions

Part 1. Density of Bar and Two Cubes

1. How do the densities of Cube 1, Cube 2 and the Bar compare?

   The densities of all are nearly equal.

2. From the data collected, are any or all of the objects composed of the same material? How do you know?

   The composition of all of the objects are most likely the same because the densities are the same or nearly the same.

3. Use the following density table to identify the composition of the objects.
   {12000_Answers_Table_4}
4. Once each item has been identified, use the following equation to determine the accuracy of your calculated density measurement.
   {12000_Answers_Equation_4}
5. What are some possible errors in the density determination?

   Limitations of the precision of the ruler and balance and the estimated uncertainty of the measurements are all possible sources of error.

Part 2. Density of Spheres

6. Was the same amount of water displaced by each of the spheres? Why or why not?

   The same amount of water was not displaced for each sphere. The volumes of the spheres were different.

7. Given your results, are the two spheres composed of the same material? Explain.

   Yes, the two spheres are most likely composed of the same material.

8. What is the composition of the spheres? Use the density chart from Question 3 to determine the answer.
   The spheres are composed of glass. The density is approximately 2.6 g/cm³.

Part 3. Density of Mineral Samples

9. Compare the densities of the mineral samples. Do the shapes of the minerals have any effect on their densities?

   No, the shape of each mineral does not affect density because the density is a physical property of the mineral.

10. If the density of a mineral ten times the size of one of the samples you tested was measured, would it have the same density as the smaller mineral? Explain.

    Yes. Given no other interferring factors (e.g., impure samples), the density would be equal no matter what size the mineral sample.

11. What are some possible sources of error when measuring the density of the mineral samples by water displacement?

    The mineral may not be composed entirely of one substance. Human error in measuring the water level correctly, etc.

12. In general which method (direct measurement and collection or displacement) do you think gives the best volume measurement? Why?

    Answers will vary.

Introduction

How is density measured? What factors are involved in finding the density of objects of different sizes, shapes and composition? Several experiments will be performed in this activity to answer these questions.

Concepts

• Measurement
• Density
• Percent error
• Mass
• Volume

Background

In this activity, the mass, volume, and density of several objects will be determined and compared by two methods: direct measurement and water displacement. In Part 1, the volume of two cubes and a bar will be calculated using Equation 1. The length, width, and height will be measured using a metric ruler.

The mass of the three objects will be found using a balance and the density of each object will then be calculated using Equation 2. Density, which is defined as an object’s mass divided by its volume, is a characteristic property of a material. Solids that have the same physical appearance or objects of different shapes and sizes may be identified by their densities. The density of a solid is commonly expressed as g/cm³.

In Part 2 of this experiment, the volume two spheres of different sizes will be determined by water displacement. Using Equation 3, the volume of each sphere may be calculated. The mass and volume of the spheres will then be used to determine the density and identity of each sphere.

In Part 3 of this activity, the density of unknown rock samples will be found using the water displacement procedure from Part 2.

Materials

Safety Precautions

Although this activity is considered nonhazardous, always follow proper laboratory safety procedures.

Procedure

Part 1. Density of a Bar and Two Cubes

1. Measure the length, width and height of cube 1 to the nearest 0.5 mm (0.05 cm). Record the values in Data Table 1.
2. Using Equation 1 from the Background, determine the volume of cube 1. Record the volume for cube 1 in Data Table 1.
3. Find the mass of cube 1 using a balance. Record the mass to the nearest 0.1 g in Data Table 1.
4. Determine the density of Cube 1 by using the calculated volume of cube 1 from step 2 and the mass of cube 1 from step 3 (see Equation 2 in the Background). Record the density in Data Table 1.
5. Repeat steps 1–4 for cube 2 and also the Bar. Record all information in the appropriate spaces in Data Table 1.
6. Answer the questions for Part 1.

Part 2. Density of Spheres

7. Obtain the two spheres. Record the similarities and differences of the two spheres in Data Table 2.
8. Place a weighing dish (or other similar item) on a balance. Tare or rezero the balance. Place sphere 1 (the smaller sphere) in the weighing dish and record the mass to the nearest 0.1 g in Data Table 2.
9. Fill a 50- or 100-mL graduated cylinder about half-way with water. Record the initial volume of water (in mL) in Data Table 2. Record the volume to the nearest tenth of a milliliter.
10. Carefully place sphere 1 in the graduated cylinder. It works best to tip the graduated cylinder and allow the sphere to roll down the side.
11. Record the new volume of water in the graduated cylinder in Data Table 2. This is the volume of the sphere plus the water.
12. Calculate the volume of sphere 1 using Equation 3 (see the Background section). Record the volume in Data Table 2.
13. Calculate the density of sphere 1 using Equation 2. Record the density of sphere 1 in Data Table 2.
14. Repeat steps 8–13 for sphere 2. Record all information in Data Table 2.
15. Answer the questions for Part 2.

Part 3. Density of Mineral Samples

16. Follow the procedure in steps 7–14 for the given mineral samples.
17. Record all information in Data Table 3.
18. Answer the questions for Part 3.

Student Worksheet PDF

12000_Student1.pdf