Using Density to Identify Metals
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Elaine Hunter Zenos Colman School
4655 South Dearborn Street
Chicago, Illinois 60609
(Recommended grade levels 6-8)
To teach the techniques of measuring the density of some common metals.
To identify a metal by its density.
graduated cylinders (10, 25, 50, and 100 ml)/group
electronic balance (one for the class)
calculators (one for each group)
unidentified metals (iron, copper, aluminum, lead, pyrite)
medium size rock
two pan balance
lab worksheet to record mass, volume and density
Prior to teaching the lesson ask the class to bring in some gold jewelery that
they would like to have appraised. The day of the lesson write the following
riddle on the board: Which weighs more, a pound of feathers or a pound of
rocks? This riddle should be solved before the lesson begins. Discuss the
solutions to the riddle with the class. Show the class a medium size rock, and
ask a volunteer to balance the rock with cotton balls using a two pan balance.
Discuss the results with the class. Elicit reasons why so many cotton balls
were needed to balance the medium size rock. Discuss the meaning of density as
a ratio of mass to volume. Tell the class that density can be expressed
mathematically: D=M/V. Practice calculating a few density problems. Density is
like a finger print for metals. If the density of a metal is known, it is a
good clue to the identity of the metal. Give the class a handout that explains
why prospectors during the goldrush in 1848 experienced difficulty in finding
gold. Ask the class what was mistakenly found. How can we distinguish "Fool's
Gold" from pure gold? Let the class examine samples of "Fool's Gold" and
discuss properties of the sample that might have led prospectors to believe they
had pure gold.
Tell the story of an envious king who was duped by some crafty crooks who knew
how to make some inferior metals look like gold, silver, or platinum. In the
lab the class will perform experiments with metals to determine which metals
were subtituted for the metals used in the king's crown, scepter, breast plate
and sword. They will do this by measuring the mass and volume and calculating
The class will average the density results and make a standard for metals.
The class will compare their results with those of experts.
The class will determine which metals were used as substitutes for the king's
The class will use the data chart to compare the mass and volume to the metal
having the greatest density with that of the lowest density, and see if there
is a relationship.
Each student should have completed his lab sheet and have calculations for
densities of the metals.
Each student should have performed each step in finding density in the lab.
The teacher should observe involvement of the students during class discussions.
Marshall, Robert H. and Jacobs, Donald H. Physical Science Investigating Matter
and Energy Media Materials, Inc., Baltimore, Maryland, l987
Bernstein, Leonard; Schacter, Martin; Winkler, Alan; Wolfe, Stanley. Concepts
and Challenges in Science Book 2, Cebco Standard Publishing, Fairfield, New