Density Lab

What’s in a Penny?

I. Introduction Density is a physical property of all materials. Any compound or mixture is going to have a specific density at any given temperature. An analyitical chemist can use a compound’s density to determine exactly what chemical he or she has been given. Today’s activity will show you how to use a technique called water displacement to determine the volume of a given substance. That volume data will then be combined with ass readings to determine the densities of various metals. Ultimately, you will use both density and other observations to determine what pennies are made of. II. Objective: o TLW apply proper lab technique to determine the density of known materials o TLW apply proper lab technique to determine the density of an unknown material o TLW use previously gathered density data to determine the identity of an unknown material Caution: We will be working with Bunsen burners in lab today. There is to be not horse play or practical jokes. Safety goggles are to be worn at all times. There will be one warning and then you will be removed from the lab. NOTE: The copper shell of the pennies will be heated to extreme temperatures. DO NOT TOUCH THE PENNIES WITH YOUR HANDS AFTER IT HAS BEEN HEATED UP! Materials Needed: Iron nails Aluminum pieces Zinc pieces Copper pennies (before 1982) “Hollow pennies” (after 1982) 50 ml graduated cylinder Bunsen burner Crucible 2 Tongs Striker

Procedure: 1. Obtain 4 nails, 8 copper pennies, 8 hollow pennies, and a reasonable sample of both zinc and aluminum. 2. Use the scales at the front of the classroom to determine the mass of each of these samples. Record your mass data on the data table (bottom of this page). 3. As the mass of each sample is recorded send the materials back to your lab bench. 4. Partially fill a graduated cylinder with water (Note: It may be useful to fill the graduated cylinder to the same level every time to minimize confusion) 5. Record the water level in the graduated cylinder, and then place a sample in the cylinder. Record the new water level. The difference is the volume of your sample. 6. Repeat steps 4 and 5 for each sample. 7. Now you have both the mass and the volume of each sample. Use this data to calculate the density of each sample. 8. As the density calculations are being performed, have a group member dry each sample and return them to the instructor’s table. DO NOT return the hollow pennies. 9. Ignite your Bunsen burner and tip at a 45 degree angle (do not hold the shaft of the Bunsen burner. 10. Use the tongs to hold a penny in the hottest part of the flame (the inner blue cone) while at the same time holding a crucible (with tongs) under the penny. The outer layer of the penny will melt and bend. Allow this to happen. After a while, a metal liquid will fall out of the penny. Try to catch that liquid in the crucible as it falls out of the penny. If it misses the crucible it is not a problem, but DO NOT touch the metal with your hands. Place it in the crucible with the tongs. Run water over what remains of the penny in the tongs and set that aside. 11. Determine the density of both of these metals. (create your own data table) 12. If you finish early. Retrieve a copper penny. See what happens if you hold that penny up to the flame. DO NOT touch the penny until you have run cold water over it for 30 seconds!!!

Mass (g)

Volume of cylinder before sample added (ml)

Volume of cylinder after sample added (ml)

Volume of sample (ml)

Density of sample (g/ml)

Iron Nails Aluminum Zinc Copper Pennies Hollow Pennies Shell of Penny Inside of Penny

Questions to be addressed in the conclusion 1. What metal is the coating of the hollow made of? 2. What evidence leads you to that conclusion? (Provide more than density data) 3. What metal makes up the inside of a hallow penny? 4. What evidence leads you to that conclusion? (Provide more than density data)