Determining the Density of Unknown Substances

Transcription

1 Determining the Density of Unknown Substances Introduction: Most of the elements on the periodic table are metals and solids. These elements have observable properties that make it possible to identify an unknown element. Density is one of the properties that can be used to identify an unknown. As you know, density is the ratio of mass to volume. In equation form: Density = Mass Volume. Purpose: In this lab, you will find both the mass and the volume of several unknown s. From these measurements, you will calculate the density of the unknown s. Using the chart below, you will identify your unknown s. Name of Density Name of Density Aluminum 2.70 g/cm 3 Oak g/cm 3 Copper 8.96 g/cm 3 Nylon 1.13 g/cm 3 Brass 8.0 g/cm 3 Pine g/cm 3 Steel 7.6 g/cm 3 Poplar g/cm 3 Acrylic g/cm 3 PVC g/cm 3 Procedure: 1. You have been given several unknown s. You will determine both the mass and the volume of each and record your data in the table below. 2. Use the balance to determine the mass of each piece of. 3. Use the ruler to measure the length, width, and height of each cube and calculate its volume (LxWxH) 4. Calculate the density of each piece of. Show your calculations and your answers in the data table. D = m/v 5. Identify the unknown by comparing your calculated density with the densities listed in the table in the introduction. 6. Record the name of the unknown (now the known!) in your data table. Names: Class: Date:

2 Data Table: Determining the Density of Unknown Substances Substance A Mas s (g) Volume (cm 3 ) Density Name of length width height Volume of Substance B C D Analysis Questions: 1. Did the density that you calculated for each match the densities given in the table exactly? If not, explain why your calculated density was different than the density given in the table. 2. Determine the percent error in each of your calculations. To determine your percent error, use this equation: Percent Error = Observed Value True Value x 100% True Value Percent Error for A: Percent Error for B: Percent Error for C: Percent Error for D: 3. From the introduction: Density is one of the properties that can be used to identify an unknown. What are some other observable properties that can be used to identify these s?

3 4. Is density a physical property or a chemical property? How can you tell? 5. Do you think that density is a reliable method of identifying all unknown s? Explain your answer. 6. Many s expand when they are heated. How would this affect the density of the? Challenge Question: You discover a piece of jewelry that you think might be made of silver. You place the item on a balance and determine that it has a mass of 12.2 grams. It displaces 1.9 cm 3 of water when placed in a graduated cylinder. Is this item made of pure silver? Challenge Question: Copper has a density of 8.96 g/cm 3. What would be the mass of a piece of copper whose volume is 14.7 cm 3? Graphing Reinforcement:

4 A student was given 5 pieces of aluminum of various sizes. The student determined the mass and volume of each piece of aluminum. This data is seen in the chart below: Mass and Volume of 5 pieces of Aluminum Piece Mass Volume g 2 ml g 5 ml g 3.5 ml g 9.5 ml g 7 ml Graph this information on the graph below, placing volume on the x-axis and mass on the y-axis. 9. Aluminum has a fixed density. Are the mass and volume directly proportional or indirectly proportional for a fixed density? 10. Using the graph above, determine the mass of a piece of aluminum having a volume of 8 ml. 11. Using the graph above, determine the volume of a piece of aluminum having a mass of 16 grams. 12. What is the mass of a sample having a volume of 11 ml?

5 Lab Activity Conclusion: Write a 5-7 sentence conclusion discussing what were the major objectives you learned about, something that you found particularly interesting or surprising, and what you would like to learn about next in this topic.