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Purpose:
To determine the difference in composition of pennies that
by all appearances are identical will require you to invoke Archimedes
displacement principles (the guy who said Eureka! after figuring
out if the king's crown was truly pure gold).
Setup:
50 mL graduated cylinder
10 pre-1983 pennies
10 post-1983 pennies
gram scale
Procedure:
- Find the mass of the 10 pre-1983 pennies
- Find the mass of the 10 post-1983 pennies
- Carefully fill the graduated cylinder to EXACTLY 30 mL with
water
- Carefully place the 10 pre-1983 pennies into the graduated
cylinder and record the change in water volume in milliliters
- Empty the cylinder and dry off the pennis
- Repeat steps 3-5 with the 10 post-1983 pennies
- Compute the density for each of the 2 groups of pennies
- Determine and verify % composition of the mystery element
for each type
Data:
| |
mass (g) |
displacement (mL) |
density (g/mL) |
| 10 pre-1983 pennies |
|
|
|
| 10 post-1983 pennies |
|
|
|
Analysis:
It turns out that before 1983 pennies were 90% copper. Now they
are only 10% copper! What could this cheaper mystery element be?
What is the density of copper? ___._ g/mL
Pre-1983 pennies are mostly (element) ___________
Guess what element post-1983 pennies are mostly ___________
This mystery element (X) has a density of ___._ g/mL
Verify % composition of this mystery element X:
PRE-83 : ( .9 x 8.96 ) + ( .1 x X ) = ___._ g/mL
POST-83 : ( .1 x 8.96 ) + ( .9 x X ) = ___._ g/mL
Compare this with your lab densities:
__________________________________________________________________________
Conclusion:
Finally, update your website with the details of this lab experience
including a descriptive summary, all data, calculations and %
conclusions! The instructor will grade this lab
web entry according to this rubric.
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