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 à
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
à
Zn + HCl à
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.)