ChemLab 2 –

Using Density to Find the Thickness of a Wire


The thickness of wire often is measured using a system called the American Wire Gauge (AWG) standard. The smaller the gauge number, the larger the diameter of the wire. For example, 18-gauge copper wire has a diameter of about 0.102 cm; 12-gauge copper wire has a diameter of about 0.205 cm. Such small diameters are difficult to measure accurately with a metric ruler. In this experiment, you will plot measurements of mass and volume to find the density of copper. Then, you will use the density of copper to confirm the gauge of copper wire.

Problem:  How can density be used to verify the diameter of copper wire?    

Objectives:
• Collect and graph mass and volume data to find the density of copper.
• Measure the length and volume of a copper wire, and calculate its diameter.    
• Calculate percent errors for the results.    

Materials:
tap water        metric ruler    50-mL graduated cylinder        pencil
small cup, plastic    balance     copper shot      
copper wire (12- gauge, 18-gauge)    graph paper

Pre-Lab:
1. Read the entire CHEMLAB

2. What is the equation used to calculate density?    
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3. How can you find the volume of a solid that has an irregular shape?
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4. What is a meniscus and how does it affect     volume readings?    
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5. How do you find the slope of a graph?  
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6 If you plot mass versus volume, what property of matter will the slope of the graph represent?
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7. A piece of copper wire is a narrow cylinder. The equation for the volume of a cylinder is
V= π r2 h
where V is the volume, r is the radius, h is the height, and π (pi) is a constant with a
value of 3.14.   Rearrange the equation to solve for r.
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8. What is the relationship between the diameter and the radius of a cylinder?
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Procedure:
Record all measurements in the data tables.

PART I – DENSITY OF COPPER
1. Pour about 20 mL of water into a 50-mL graduated cylinder. Read the actual exact volume (Starting volume). Don’t forget significant digits in this measurement!!! (Or any others) This volume will be the same for the entire data table.

2. Find the mass of the plastic cup.  (Mass of cup)

3. Add about 10 g of copper shot to the cup and find the mass again. (Mass of Cu and cup)
Calculate the Exact mass of copper by subtracting Mass of cup from Mass of Cu and cup.

4. Pour the copper shot into the graduated cylinder and read the new volume. (Ending volume)
Calculate Total volume of Cu by subtracting Starting volume from Ending volume.

5. Repeat steps 3 and 4 three times, each time adding more copper to the graduated cylinder.  By the end of the four trials, you will have about 40 g of copper in the graduated cylinder.  Each time more copper is added, keep a running total of the amount of copper in the graduated cylinder in the column labeled Total mass of Cu

6. Calculate the Density of copper for each trial using Total mass of Cu / Total volume of Cu.
Average these values.  Calculate the % error by the following formula.  Use 8.96 g/ml as the accepted value.
          Accepted value – Experimental value   x 100
        Accepted value

7. Graph total mass versus total volume of copper. Put mass on the y-axis and volume on the x-axis.  Draw a line that best fits the points.  Then use two points on your line to find the slope of your graph.  Because density is equal to mass divided by volume, the slope will give you the density of copper.   Find the % error by using this method for finding density.  

PART II – DIAMETER OF COPPER WIRE
8. Obtain a piece of 12-gauge copper wire and a piece of 18-gauge copper wire. Use a metric ruler to measure the diameter (in cm) of each wire.  Record these values in the table for Measured diameter

9. Use a metric ruler to measure the length (in cm).
10. Find the mass of each piece of copper wire.  Record these values
11. Calculate the volume of each wire using the density formula and the accepted value of density for copper.
12. Calculate the radius of each of the wires using the volume of a cylinder formula.
13. Calculate the diameter of each of the wires using the diameter formula.

14. Calculate % error for diameter using the accepted values in the introduction of this lab.

Cleanup and Disposal
14. Carefully drain off most of the water from the graduated cylinder. Make sure all of the copper shot remains in the cylinder. Pour the copper shot onto a paper towel to dry. Both the copper shot and wire can be reused.

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