SOLIDS: Mass, Volume and Density Measurements

Transcription

1 CHEM 1411 Lab Solids: Mass, Volume, and Density 23 SOLIDS: Mass, Volume and Density Measurements A. Overview Review Sections in your textbook (Chemistry: The Central Science, 9th Ed., Brown, LeMay, Bursten, & Burdge) This experiment will introduce you to a very important concept in science, especially chemistry: DENSITY. Density is the relationship between the mass of an object and the volume which it occupies. Solid substances generally have the greatest density, normally in the range of 1-25 g/cm 3. Most liquids have densities between g/ml, while the density of most gases under normal conditions of pressure and temperature is less than 5 g/l. The density of a substance is a valuable tool in determining the identity of a substance. The laboratory techniques which you will perform are provided as two exercises, each of which you should be able to complete in minutes. It is not necessary that you do the two exercises in order as they appear in the laboratory manual, but you must complete both exercises during the laboratory period. NOTE: Each experiment for CHEM 1411 is written for students to work with one, two, or three partners. This experiment requires groups of three or four. Please do not work alone unless otherwise instructed. You will record your measurements and results in the Data Tables as Trial 1. Your lab partners measurements and results are recorded as Trials 2, 3, and 4. In Exercise 1, you will determine the density of a solid of regular geometric shape, and identify the composition of the solid by comparing the density with reported values. In Exercise 2, you will determine the density of pennies by water displacement. B. Procedures Exercise 1. Density of A Regular Solid Apparatus: Safety Equipment: Chemicals: Electronic balances, beakers, regular-shaped solids, vernier calipers aprons, goggles None Objectives: In this exercise you will: 1. learn to operate the electronic balance properly to measure the mass of an object. 2. learn how to read a vernier caliper 3. calculate volumes and densities from measurements of mass and distances 4. provide answers to the proper number of significant digits

2 CHEM 1411 Lab Solids: Mass, Volume, and Density 24 Instructions: The electronic balances are very sensitive to bumps and moves, etc. DO NOT MOVE OR UNPLUG THE ELECTRONIC BALANCES. ONLY YOUR INSTRUCTOR MAY MOVE OR UNPLUG THE BALANCES. 1. Obtain a vernier caliper and a regular-shaped solid (bar, cylinder, or sphere) from the cart at the front of the laboratory. Record the number or letter of the solid on your Data Sheet. 2. Measure the mass of the cylinder on an electronic balance to the nearest gram. a. Place an empty 50- or 100-mL beaker on the balance pan. Press the "Tare" button until the digital display reads "0.000 g". b. Place the solid inside the beaker. Record the mass of the solid directly from the digital display on the Data Sheet. c. Pass the solid to one of your partners, who will weigh the solid on a different balance. d. Repeat this process until each partner has weighed the solid. 3. Determine the average mass from the measurements and record this value on the Data Sheet. Each member of the group will perform the following steps with a different vernier caliper. 4. Place the solid between the teeth of the vernier caliper, and record the measurement of one dimension (length, diameter, etc.) to 0.01 cm in the Data Table under Trial 1. a. Find the zero mark on the sliding scale. The first two digits are found on the fixed scale above In the drawing, the "0" on the sliding scale is between 3.3 and 3.4 on the fixed scale. b. Find the line on the sliding scale which is aligned with a line of the fixed scale. In the drawing, this is the third line past the "0". c. The measurement is therefore 3.33 cm. 5. Rotate the solid to measure a second dimension in the same manner. Measure the height of the cylinder to the nearest 0.1 mm. Record as a second dimension under Trial 1. If necessary, repeat this step for the third dimension. a. If the solid is a rectangular shaped bar, you will need to measure length, width, and height. b. If the solid is a cylinder, you will measure the diameter and height. c. If the solid is a sphere, you will only need to measure the diameter.

3 CHEM 1411 Lab Solids: Mass, Volume, and Density Pass the solid to another member of the group, who will repeat steps 4 and 5. This sequence is repeated until each student has completed the measurements. 7. Determine the average value for the three dimensions and record this value on the Data Sheet. Calculate the volume of the solid from the average values. Use the average mass and average volume to determine the density of the solid. 8. Return the solid and caliper to the cart. 9. Determine the possible identity of the solid from the experimental density. Calculate the % error from the accepted density. Exercise 2. Density of a Solid of Irregular Geometric Shape by Water Displacement The density of water at room temperature is 1.00 g/ml. A solid with a density greater than water will displace an equal volume of water as the object. Apparatus: Safety Equipment: Chemicals: Electronic balance, beaker, graduated cylinder, irregular solid aprons, goggles tap water Objectives: In this exercise you will: 1. measure the volume of an irregular solid by water displacement. Instructions: 1. Place an empty 50-mL beaker on an electronic balance and tare the balance to zero. 2. Add grams of the irregular solid to the beaker. Determine the mass of the solid to 0.01 gram. 3. Pour approximately 30 ml of tap water into your 50-mL graduated cylinder. Record the volume of the water in the cylinder (estimate to the nearest 0.1 ml) on the Data Sheet. 4. Carefully slide the solid into the cylinder containing the water. Be careful that you do not spill any water. In addition, be careful that you do NOT BREAK the graduated cylinder. 5. Record the volume of the water level in the graduated cylinder with the solid inside to the nearest 0.1 ml on the Data Sheet. 6. Slowly pour the water from the graduated cylinder in the sink. Collect the solid on a paper towel. Dry the solid and pour it into the Wet Irregular Solid container. 7. Repeat steps 1 6 with a gram sample of irregular solid and 25 ml of tap water. 8. Determine the density of the solid from each trial, and the average density of the solid.

4 CHEM 1411 Lab Solids: Mass, Volume, and Density 26 Exercise 3. Density of Pennies by Water Displacement The density of water at room temperature is 1.00 g/ml. A solid with a density greater than water will displace an equal volume of water as the object. Apparatus: Safety Equipment: Chemicals: Electronic balance, graduated cylinder, weighing boat (paper) aprons, goggles tap water Objectives: In this exercise you will: 1. determine the density of pennies by water displacement. The following is a brief chronology of the penny. The information is taken from the following website. The Composition of the Cent Following is a brief chronology of the metal composition of the cent coin (penny): The composition was pure copper from 1793 to From 1837 to 1857, the cent was made of bronze (95 percent copper, and five percent tin and zinc). From 1857, the cent was 88 percent copper and 12 percent nickel, giving the coin a whitish appearance. The cent was again bronze (95 percent copper, and five percent tin and zinc) from 1864 to (Note: In 1943, the coin's composition was changed to zinc-coated steel. This change was only for the year 1943 and was due to the critical use of copper for the war effort. However, a limited number of copper pennies were minted that year. You can read more about the rare, collectible 1943 copper penny in "What's So Special about the 1943 Copper Penny.") In 1962, the cent's tin content, which was quite small, was removed. That made the metal composition of the cent 95 percent copper and 5 percent zinc. The alloy remained 95 percent copper and 5 percent zinc until 1982, when the composition was changed to 97.5 percent zinc and 2.5 percent copper (copper-plated zinc). Cents of both compositions appeared in that year. Instructions: 3. Place an empty weighing boat on an electronic balance and tare the balance to zero.

5 CHEM 1411 Lab Solids: Mass, Volume, and Density Choose approximately 20 pennies from various years from the supply beakers. The beakers are labeled as and Add pennies to the weighing boat. Determine the mass of the pennies to 0.01 gram. 3. Pour approximately 30 ml of tap water into your 50-mL graduated cylinder. Record the volume of the water in the cylinder (estimate to the nearest 0.1 ml) on the Data Sheet. 4. Carefully slide the pennies into the cylinder containing the water. Be careful that you do not spill any water. In addition, be careful that you do NOT BREAK the graduated cylinder. 8. Record the volume of the water level in the graduated cylinder with the solid inside to the nearest 0.1 ml on the Data Sheet. 9. Slowly pour the water from the graduated cylinder in the sink. Collect the pennies on a paper towel. Dry the solid and pour it into the Wet Pennies container. 7. Calculate the density of the pennies. Compare your results with your lab partners, and calculate the average density of the pennies for the two time frames requested.

6 CHEM 1411 Lab Solids: Mass, Volume, and Density 28 C. Laboratory Report The laboratory report is the final stage of telling what you do in the laboratory. It should provide background information, collected data, and a discussion, plus questions. Refer to the description of laboratory reports on page x of the Introduction section. The following items are specific to this experiment. Your instructor will inform you of the URL containing the EXCEL spreadsheet which you must complete as part of the experiment. The spreadsheet can be printed and inserted in the results section as the data. Calculated values Sample calculation of each type, complete with units Identity of unknown(s) % Error catculations Discussion and Conclusions Discuss your results, justifying your choice of unknown identification from the experimental data and results. Include a discussion of possible sources of error, based upon % error determination. Questions Answer the following questions at the end of your laboratory report. 1. Why was it necessary to measure each dimension of the regular solid to 0.01 cm? How will your answers be affected if you chose only to measure the value to the nearest 0.1 cm? 2. What is Archimedes' Principle? Briefly describe how a king or queen could use the procedure from the laboratory to determine if pure gold was used to make his (her) crown. 3. The calculated values from the spreadsheet may be different from the values that you determined during the laboratory period. Briefly describe any differences in values and provide a plausible explanation for the differences. Densities of Common Materials

7 CHEM 1411 Lab Solids: Mass, Volume, and Density 29 NAME SYMBOL DENSITY (g/cm 3 ) Aluminum Al Bismuth Bi 9.75 Chromium Cr 7.18 Cobalt Co 8.90 Copper Cu 8.89 Diamond C 3.51 Graphite C 2.25 Gold Au Iron Fe 7.85 Lead Pb Magnesium Mg Manganese Mn 7.21 Mercury Hg Nickel Ni 8.90 Platinum Pt Tin Sn 7.30 Zinc Zn 7.11 Brass Cu/Zn 8.0 Steel Fe/C/Mn 7.6 Acrylic Clear 1.18 Nylon White 1.13 PVC Grey 1.40 Wood (Oak, Pine, Poplar) A sample copy of data for the Excel spreadsheet is given below. When you open the spreadsheet, you will input data into the cells surrounded by outlines. The other cells are designed to automatically calculate the values for you.

8 CHEM 1411 Lab Solids: Mass, Volume, and Density 30 Name: Density of a Regular Geometric Solid Bar Sample Number Trial Mass g Length cm Width cm Height cm Volume cm 3 Density g/cm 3 Average Density 2.80 g/cm 3 Identity of Unknown Sample Aluminum Accepted Density 2.71 g/cm 3 Percent Error 3.28%

9 Laredo Community College Science Department CHEM 1411 Laboratory 31 SOLIDS: Mass, Volume, and Density Measurements Name: Section Date Partner(s) Show all calculations. Exercise 1. Density of a Solid of Regular Geometric Shape Shape of Solid Sample Number Sample Color Student 1 Student 2 Student 3 Student 4 Average Mass g g g g g (1) cm cm cm cm cm (2) cm cm cm cm cm (3) cm cm cm cm cm Volume cm 3 cm 3 cm 3 cm 3 cm 3 Density g/cm 3 Identity of your unknown is. Calculate the % error for your experimental density. %. Show sample calculations below.

10 CHEM 1411 Lab Solids: Mass, Volume, and Density 32 Exercise 2. Density of a Solid of Irregular Geometric Shape Sample Number Trial 1 Trial 2 Mass of Solid g g Volume of Water ml ml Volume of Water with Solid ml ml Volume of Water Displaced ml ml Volume of Solid cm 3 cm 3 Density of Solid g/cm 3 g/cm 3 Average Density g/cm 3 % Error % Show sample calculations below. Exercise 3. Density of Pennies by Water Displacement Sample Number

11 CHEM 1411 Lab Solids: Mass, Volume, and Density 33 Student 1 Student 2 Mass of Pennies g g Volume of Water ml ml Volume of Water with Pennies ml ml Volume of Water Displaced ml ml Volume of Pennies cm 3 cm 3 Density of Pennies g/cm 3 g/cm 3 Average Density g/cm 3 Years: Student 3 Student 4 Mass of Pennies g g Volume of Water ml ml Volume of Water with Pennies ml ml Volume of Water Displaced ml ml Volume of Pennies cm 3 cm 3 Density of Pennies g/cm 3 g/cm 3 Average Density g/cm 3 Based upon the years of the pennies used, approximately what value would you expect for the density of the pennies? g/cm 3 What are your percent errors? (1) % ; (2) % ; (3) % ; (4) % Show sample calculations below.