Name:____________________________ 80/1200
Objective: To measure the density differences between pennies made in 1982 and before with those made in 1983 and after. Using these differences in density we will determine the metal used inside these new pennies.
Background:
The government now makes pennies that are different from the ones made before 1983. The older pennies were made of an alloy of copper which was nearly pure copper. Since then, they have been made with a thin outside coating of copper (approximately 2% of the metal in the coin) over an inner core of a different metal (which is our unknown).
The pennies appear identical in size and volume but the mass difference results in measurable differences in the density of pennies.
We will carefully measure the mass and volumes of the old pennies and new pennies and we will calculate the density for each set of pennies. This density will allow us to determine the unknown metal that is inside the new pennies.
The government changed to this metal to lower the costs of penny production, but recently the cost of this metal has jumped and it now costs about three cents in metal to produce two pennies!
Procedure:
1. Obtain 25 old pennies (dated before 1982) and 25 new pennies (1983 or newer).
Make sure that these pennies are not “cruddy” as that will cause measurement error.
2. Measure the mass of groups of these pennies, five pennies at a time (5, 10, 15, 20, + 25 pennies) and then record this data in a data table.
3. Fill a 100-mL graduated cylinder to the 40.0-mL mark with water. Be careful.
4. Measure the volume of these sets of pennies, five at a time. Gently slide the pennies into the graduated cylinder as shown by your teacher. Do NOT splash the pennies into the tubes. Record the volumes of the pennies into your data table as well
5. Dry the pennies when you have finished. DO NOT PUT WET PENNIES AWAY.
6. Repeat the whole process for the set of the newer pennies.
7. Be neat when you make your data tables so that your information will be available to you when you need it. Be sure to use the PROPER units in your data tables.
8. Note: 1.00 mL water = 1.00 cm
3
water, because 1.00 mL = 1.00 cm
3
Sig Figs Matter: when measuring with the electronic balances, the measures go to the 100th gram.
When using the graduated cylinders, measure to the 10th place in mL. When calculating your measured densities, significant figures of the answer will be limited to the lowest number of SF in the numbers you multiply in the calculations.

Density by Displacement Lab Data Tables
3
3

Data Interpretation—Graphing
Each student will create a large graph plotting mass as a function of volume (mass on the vertical scale or Y-axis, volume on the horizontal scale or X-axis). It is imperative that you set the graph up correctly.
Since density is equal to mass over volume, and the fact that the slope of our graph is equal to the change in Y over the change in X, and since on this graph Y is mass and X is volume, the slope of the lines will be equal to the measured density of the pennies.
By calculating the slope of each line, we will actually be calculating the measured density of each type of penny (old and new). Here, the slope IS THE SAME THING as measured density. slope = ∆ Y
∆ X
Density = ∆ mass
∆ volume
Density = m
1
—m
2
gm
v
1
-v
2
cm
3
Put the 5 points of data for the old pennies on the graph first, then draw the BEST FIT LINE, do not just connect the dots. This line must be straight! The line is your AVERAGE (by eye) of the data points. Then put the second set of five dots of data on the graph and draw ANOTHER BEST FIT
STRAIGHT LINE. Label each line - old and new pennies. Give your graph a sensible title and be sure each axis has a label with units. m
1
, v
1
Y
MASS
grams m
2
, v
2
VOLUME mL
X
1
1
2
2
To calculate slope, use data points FROM YOUR BEST FIT LINE, which do not necessarily come from your actual data tables. The best fit line MUST be straight, it represents the
CONSTANT called density.
We will NOT use the density equals mass over volume formula for any reason during this experiment. The calculations of slope will be our “average density” for our 5 measurements.

CALCULATIONS and QUESTIONS for this lab report, SHOW THE MATH!!!
1. What is the slope AND the measured density for the “old” penny line?
2. What is the slope AND the measured density for “new” penny line?
3. If the old pennies are pure copper, what is the % Error for your measured density?
4. Using your reference table S, make a list of the 6 metal elements with a density close to your measured density from question 2. (symbols and density values please)
5. Choose the one metal on that list which is closest to your measured density.
6. The metal in the new pennies is zinc. What was your percent error?
7. Why is it important to put the pennies into the cylinders slowly, without splashing?
8. If you had a small hunk of nickel metal, and measured the volume to be 84.00 mL, what would be its mass (write the formula, use correct significant figures and proper units please). Hint: the density values on table S are equalities, not measurements. Watch your SF!
This lab report cover page
Includes
Title, intro sentence about why we are doing this lab grading/points
1 + 1 = 2 page 2 page 3 data tables for masses and volumes large graph, proper labels
4
6 page 4 eight problems from above 8 page 5
:
•
What did you measure
•
What did you calculate
•
What is your % error (and why)
•
What can you conclude or decide from this lab work?
•
All lab conclusions MUST include YOUR numbers, not just words.
deduct
5 points if late this lab is due on:
5
25 points