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The great penny experiment

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Lab Experiment #2:  The Copper Penny Experiment

I.    Purpose

A.      To experimentally determine the density of a solid

B.       To determine the percent composition of post 1982 pennies

C.       To study the nature of chemical reactions

 

 

II.      APPARATUS/MATERIALS

 A.   Digital balance

D.     Vernier calipers

E.      Metal scraper (Mr. Painter will use)

F.       1 graduated cylinder, 2 large test tubes

G.      Pre-1982 and post-1982 penny

H.     20-ml of 0.05 M HCl (10-ml per test tube)

I.        Filter paper

 

 

III.   BRIEF EXPLANATION

 

You are a chemical consultant for the Federal Reserve.  The President has a few questions he needs answered so that he can decide whether or not to keep using the penny.  As such, you are asked to perform a chemical analysis of the U.S. penny.  There are a few questions you need to answer.  First, how much copper (% composition) is there in the current U.S. penny?  Next, how much copper (% composition) was there in pennies made before 1982?  Why was the penny’s composition changed?  Under current economic conditions, should the composition of the penny be changed back to the pre-1982 composition?  Should we still use the penny (based on economics)?

 

 

IV.   PROCEDURE

 

A.      Determination of densities:

 

There are two main methods to determine the volume of a solid sample.  In your lab research, you will be determining the volume and density both ways.  One involves measuring the dimensions and using a specific formula for volume (as discussed in Lab Experiment #1: The Soft Drink Experiment).  The other involves one application of Archimedes Principle.  For example, if you place a solid substance into a graduated cylinder containing a known volume of liquid, the increase in volume recorded by observation of the graduated cylinder will be equal to the volume of the solid substance.  See the specific example below:

 

                                 Volume water  = 42.1 ml

Volume water with solid = 42.4 ml

                              

Volume of solid = 42.4 ml – 42.1 ml = 0.3 ml

 

 

 

 

 

B.      Calculating % composition

 

Percent composition can be calculated from the following equation:

 

                             % Composition A=        Mass A             x  100

                                                            Total Mass of Solid

 

In this experiment, we are calculating the % composition of copper in a penny.  For example, if you experimentally determined that the penny has a mass of 1.56 g, and the hollowed-out copper shell has a mass of 0.87 g, then the % composition of copper can be calculated as follows:

 

                       % Composition of Copper =  0.87 g    x   100    =   55.8 %

                                                                        1.56 g

 

 

 

C.      Single-replacement reactions

 

In a single replacement reaction, one lone reactant switches places with one paired reactant:

 

                             A  +  BC    AC  +  B

 

For this to happen, A must be more reactive than B (in WWF terms, A has to be a stronger / tougher person to kick B out of its spot).  If A is not as reactive, then no reaction will take place.  In this experiment we have the following reactions with the penny and the HCl:

 

                        Cu +  HCl

 

                        Zn  +  HCl

 

In the lab we will be observing and discussing the products formed.  Can you predict what will happen (hypothesis).  For the activity series of elements, see page 295 in your textbook.

 

 

D.     Economics

 

The cost required to make a penny depends on the cost of the elements used to make it.  The prices of elements such as copper and zinc change as the economy changes.  These prices can be found in the newspaper and on the Internet on a daily basis.  See handouts.

 

 

E.      Pictures

 

Make sure to draw a picture of the equipment needed for the lab (graduated cylinder, test tube, electronic balance).

 

 

 

 

 

 

V.     Observations

 

Collect data for the following: 

 

                                          Pre-1982      Post 1982

      Diameter of penny:

      Radius of penny:

      Mass of penny (before rxn):

 

      Volume of penny

      (Archimedes method):

 

      Observations in HCl:

      Mass of penny (after rxn):

 

 

VI.   Results

 

Complete the following data tables:

 

 

Next, show a sample calculation for volume of the penny (measuring method), the density of the penny (any method), and the % Composition of Copper in a penny (pick one).  That is a total of three calculations.

 

 

VII.Conclusion

 

Why was the penny’s composition changed?  Under current economic conditions, should the composition of the penny be changed back to the pre-1982 composition?  Should we still use the penny (based on economics)?

 

 

VIII.         Error Analysis

 

Explain the type of error you may have had in the lab:

 

a.       Systematic error—(The equipment was faulty, had some reoccurring error, or was not accurate enough to get good data.)

 

b.       Random error—(You or your lab partner did something incorrectly or made a mistake.  For example, you spill part of a sample, you read the equipment (graduated cylinder) incorrectly, etc.)

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