LAB: The Metallurgy of Hairpins and Paperclips
Background:
Metals are a crystalline substance. The crystal structure of metals affects their physical properties such
as malleability and hardness. It is possible to alter these properties by altering the way that the crystal
structure is formed. If you cool the metal down slowly, the crystal structure will be formed in a much
more orderly fashion than if the metal is cooled down quickly, which causes a large number of
imperfections (defects) in the crystal structure. It is the way that the crystal structure is formed that
determines whether the metal is hard and brittle or soft and malleable.
The composition of metals also affects its properties. Pure metals tend to be softer and more malleable
than alloys. Alloys are solutions of different metals or, in the case of steel, metals and the element
carbon. Alloys tend to be harder than pure metals and all metals used for structural purposes are
actually alloys rather than pure metals in order to have the necessary hardness and strength. In this
experiment we will study how the rate of cooling metals affects the hardness and malleability of the
metal and attempt to use these properties to evaluate the composition of metal. We will also observe
how the bending of a sample of metal will change its malleability.
Objective: To study the affect of cooling rates on the properties of metal.
Materials: Bunsen burner, 2 hairpins, 1 paper clip, crucible tongs, beaker, evaporating dish,
Precautions: We will be working with red hot metals. Use tongs to handle metal that has been heated.
Pay attention to people around you when you are heating metal. Put any heated pieces of metal in the
evaporating dish or in the water beaker. Do not place heated metal pieces on the lab table. Goggles,
aprons and appropriate footwear must be worn at all times in the lab area. Wash your hands
thoroughly after completing the lab.
Pre Lab: Write COMPLETE SENTENCE answers to the following pre-lab questions on your Lab Report.
Questions:
1. What safety material must we wear in this lab?
2. Why are metals that are used for building materials and tools alloys rather than pure?
3. Why is the rate that metals are cooled important when you are making metal structures and
tools?
4. Explain how you are to safely pickup, hold and store the metals once heated.
Procedure: Record all observations in your Lab Report.
Part I: Hairpin Metallurgy
1. Obtain 2 hairpins and a paper clip. Compare the bending properties of the hairpin with that of
the paper clip. Record your observations in your Lab Report.
2. Heat the bend of one of the hairpins in the flame until it is red hot. When the hairpin has been
heated for at least 30 seconds, take it out of the flame and put it in the evaporating dish to cool
slowly.
3. Heat the other hairpin like you did the first one. After it has been heated for 30 seconds, plunge
it into a beaker filled with water.
4. Heat the paper clip like the hairpins. (Heat the bent part.) When it is red hot, plunge it in to the
water to cool it quickly.
5. Attempt to straighten out both hairpins. Record your observations in your notebook, making
note of the different properties of the hairpin that cooled quickly compared with the hairpin
that was cooled slowly.
6. Now attempt to straighten the paper clip. Record your observations in your lab report.
7. Dispose of the hairpins in the landfill waste basket. Return your paper clips to the front.
Questions: Chemistry Lab - Metallurgy of Hairpins and Paperclips
Discuss and answer the following questions at the end of Your Lab Report. Each person must turn in
their own Lab Report with these answers. Give complete sentence explanations.
1. Use your understanding of crystal formation to explain why cooling a metal slowly makes it soft
and malleable and why cooling a metal quickly makes it brittle.
2. If you are making a sharp tool such as a knife would you want to cool the metal quickly or slowly
in order to have it hold a sharp edge? Explain your answer based on the observations that you
made for this experiment.
3. The hairpin that you started out with had much different properties than either hairpin had
after the experiment. How do you think it was heated and cooled to give it the desirable
properties for use as a hairpin?
4. Steel is an alloy of iron and varying amounts of carbon. The carbon atoms lie between the iron
atoms in the submicroscopic structure of the steel. The hardness is directly related to the
amount of carbon in the steel. High carbon steel is hard and brittle because the carbon atoms
provide a greater number of defects in the crystal structure. Low carbon steel is softer and
more malleable than high carbon steel because it has fewer defects, making the arrangement of
the iron atoms more uniform. Based on your experiment, do you think that a paper clip is made
of high or low carbon steel?
5. Is the hairpin made of low carbon or high carbon steel? Explain completely and use
experimental evidence to support your conclusions.
6. Several years ago, a gasoline tanker truck caught fire on Interstate 5 in Lynnwood, WA. The fire
was so hot and intense that it heated the steel bridge girders. Use what you have learned about
heat treatment of steel to explain why the bridge girders needed to be replaced.
http://www.komonews.com/news/archive/Tanker-Explodes-On-I-5-InLynnwood.html?tab=video&c=y
Propose another experiment that you could do to further study the effects of cooling rate or bending on
the properties of metal.
LAB REPORT HEADINGS NEEDED:
This must be done on separate lined-paper and Must Be Done Prior to Entering Lab are in Bold.
Title of Experiment (Don’t Forget Your Name goes atop the Report, as well.)
Experiment Background (Metals and Alloys Summary)
Objective of Lab Experiment
List of Materials Needed for Experiment
Safety Precautions to Note
Pre-Lab Questions – (Given in Complete sentences)
Experiment Procedures – (In Detail because you will not take this paper into lab…only Lab
Report, which you will be Reporting on goes with you to lab area.
Experiment Observations Report – This area only needs to be Labeled before beginning, so you
can Record Observations while doing the experiment.
Post Lab Questions – Answered in Complete Sentences, after the experiment is complete.