Searching for Chemicals:  A Material Science Lesson for Chemistry Students.  Part 3:  Composition of Metal Alloys and Plastics

This Exercise is Part 3 of a series of exercises on material science.  Links to the material science exercises and three additional basic and general chemistry experiments are provided at:
Experiments and Exercises in Chemistry Courses    http://murov.info/chemexpts.htm . 
For Parts 1 or 2, please jump to http://murov.info/matsci1.htm or http://murov.info/matsci2.htm
For more web sites by Steven Murov including chemistry sites, jump to:  http://murov.info 

Part 1 of this series contains exercises designed to introduce students to online resources that contain properties of compounds.  Part 2 was to developed to provide an experience with the selection of properties of materials needed for specific applications and the search for materials with the desired properties.  Part 3 contains information on the composition of alloys and on plastics.  A selection of demonstrations and experiments related to alloys and plastics is included along with several resources that will substantially supplement the information presented below.  As mentioned in the preface to Part 1, despite the use of metal alloys and plastics in much of the "stuff" that we use in our daily lives, chemistry courses often go not give these important substances sufficient coverage.  This series of discussions and exercises has been designed to fill a small portion of the gap in chemistry courses on these topics.

CONTENTS

Properties of Alloys

Plastics

Demonstrations

Appendix A. METAL ALLOYS: Properties, Resources, Data, Information

Properties

Resources

Information

Predicting properties of alloys

Appendix B.  Plastics

Properties

Information, Links, Teacher Resources

Demonstrations

Appendix C.  Solutions to Problems

Properties of Alloys.

Using the Internet and data tables from Appendix A, fill in the following table for a selection of common alloys with the percentages of the elements in each alloy along with the properties and uses of the alloys.  Please recognize that the percentages will vary considerably and the values in the answer table are averages and not necessarily the most common or best.  Because of variability, the numbers in the answer table might not sum to 100%.  (For filled in table, jump to Table 1).

Table 1 

Thinking naively, for alloys composed of two elements, it might be expected that alloy properties could be estimated from the properties of the elements.  In Matsci1, it was observed that Mendeleev predicted properties of yet to be discovered elements by averaging properties of the elements surrounding the missing element.  This technique is not valid for the the predictions of alloys as intimate interactions among the metals causes any attempts at averaging to give questionable results.  Fill in the following table for copper, zinc and brass (70/30 copper/zinc) and discuss which properties are predictable from the values of copper and zinc.  (Please jump to filled in Table 2 and to: "Properties of brass" for discussion of soundness of predicting properties of alloys from properties of elements)

Table 2

The phase diagram to the right for a bismuth cadmium system illustrates the complexity of making melting point predictions for alloys.  Relatively speaking, the bismuth cadmium system behaves simply but clearly the melting point of the alloy cannot be estimated from the melting points of bismuth and cadmium.

For copper and zinc, the phase diagram
(see: https://www.sciencedirect.com/science/article/pii/S1110016817301618)  is considerably more complex.

Plastics

There are two common classes of polymers. Polystyrene, polyethylene, polyvinylchloride and teflon are all examples of addition polymers. For example, styrene can be polymerized by a free radical initiator (a source of a chemical having an unpaired electron). The free radical adds to the styrene creating a new free radical which then adds to another styrene and the process continues until several hundred styrenes have been added to a chain.

free radical initiator X-X g 2 X×, Ph = phenyl (benzene ring)

Polyesters and nylon belong to another class called condensation polymers. Nylon 66 can be made in the laboratory by reacting adipoyl chloride with 1,6-diaminohexane. Notice that after one molecule of each reacts, the two ends are still reactive and the left end will react with another 1,6-diaminohexane while the right reacts with adipoyl chloride. The process can continue hundreds of times. Your instructor might demonstrate this reaction to you.

Write an equation for the polymerization of chloroethene (vinyl chloride - CH₂=CHCl) to polyvinylchloride assuming that a free radical initiator (X×) is present.

I. Demonstrations.

A.  Metal Alloys.  Galium + aluminum: Google "gallium and aluminum can demonstration" for several YouTube videos.

B.  Plastic or polymer demonstrations and experiments.  Also see Experiments and Demonstrations in Appendix C.  It is recommended that the instructor perform these experiments as demonstrations as some of the chemicals are potential irritants and/or corrosive. This also minimizes the amount of waste disposal necessary.
 

1.  Alignment of Polymers.  This experiment requires two essentially identical pieces of paper.  Newspaper usually is as good as any and should be cut to reasonable size (e.g. 8 x10 inches). Holding the paper firmly in both hands, attempt to tear the paper straight down parallel to the long side.  Repeat the process with the second sheet of paper but turn the paper 90o and attempt to tear the paper downwards parallel to the sort side.  Record the details of your observations including similarties and differences between the way the paper tears.

2. Nylon synthesis

a. Prepare a solution containing 0.5 M NaOH and 0.5 M 1,6-diaminohexane. Add about 2 mL of the solution to a watch glass or evaporating dish.
b. Put a small loop in the end of a 4 inch piece of copper wire.
c. Add about 4 mL of 0.25 M adipoyl chloride in cyclohexane to the watch glass, insert the loop into the solution and slowly pull a nylon string out of the solution.

 The 1,6-diaminohexane is on the bottom in the water phase and the adipoyl chloride is in the top phase in cyclohexane. Give and account for your observations as the copper loop was lifted from the mixture.

3. Disappearing polystyrene.

Pour about 100 mL of acetone into a 600 mL beaker. Have students line up and have each one add a handful of polystyrene peanuts to the beaker. Stir between each addition.

Report and explain your observations as the polystyrene peanuts are added to the acetone.

4. Preparation of glurp, glurp' and glorp.

A 4% borax solution (sodium borate decahydrate - Na₂B₄O₇ ×10 H₂O - 20 Mule Team Borax works fine) should be available in the laboratory.
 

Glurp. Prepare 100 mL of a 1% guar gum dietary fiber solution (or 50 mL of 4% polyvinyl alcohol - dissolve by using a microwave) by adding about 1 gram of guar gum to 100 mL of water in a 400 mL beaker followed by stirring for 2 minutes. Guar gum is a vegetable gum polymer or polysaccharide composed of mannose and galactose. Add 5 mL of the borax solution to the guar gum solution and stir for several minutes. Try the following experiments with your glurp:
a. Pull the glurp slowly and record your observations.
b. Pull the glurp quickly and record your observations.
c. Mount a funnel in a ring on a ringstand. Put some glurp into the funnel and push it through the funnel. Record your observations as the glurp comes out of the funnel.
d. Try some other safe experiments, describe them, and record your observations.

Glurp’ [see David A. Katz, J. Chem Ed., 71, 891 (1994)]. Place a 20 cm by 20 cm piece of plastic cut from a melt-away plastic bag in a 200 mL beaker containing 25 mL of water. Stir vigorously until no further change is observed. Add 5 mL of the 4% borax solution and stir vigorously again. Test the glurp’ just as you tested the glurp above.

Glorp. Add 20 mL of water to 20 grams of Elmer's glue. Add 20 mL of borax solution and stir. Try some safe experiments on your glorp.

Questions on glurp, glurp' and glorp.

1. Glurp

a. Describe your observations when the glurp was pulled slowly.

b. Describe your observations when the glurp was pulled quickly.

c. Describe your observations on the funnel experiment.

2. Glurp’

a. Describe your observations when the glurp’ was pulled slowly.

b. Describe your observations when the glurp’ was pulled quickly.

c. Describe your observations on the funnel experiment.

3. Glorp

Test the glorp in as many ways as you can think of. Report your tests and observations.
 

5. Preparation of plastic worms by use of cross linking.

A 2 percent (w/w) aqueous solution of sodium alginate and a 1% (w/w) calcium chloride are needed for this experiment. Sodium alginate can be purchased or extracted from seaweed.

Extraction method. To extract alginic acid from seaweed (see Reference for possible source), dry and grind 4 g of seaweed. Add the ground seaweed to 100 mL of 2% (w/w) sodium carbonate and stir. The mixture should be allowed to stand a couple of hours (it might be best to add the solid to the sodium carbonate at the end of a lab period and then continue with the procedure the next lab period). Filter the solution using muslin cloth. To the filtrate, add 150 mL of 0.2 M HCl and stir. Filter to obtain a solid that is presumably alginic acid. As with most procedures, it is highly advisable to provide evidence that the intended product has been collected. As alginic acid is a polymer, there are very few simple measurements that can provide evidence. However, the Part E includes a method for determining the infrared spectrum of a polymer. The ir of alginic acid is available online for comparison purposes. Take an ir of alginic acid and compare the spectrum to the literature spectrum. Now add 2% sodium carbonate to convert the alginic acid to sodium alginate. Add an equal volume of 95% ethanol, filter to collect the sodium alginate and allow to dry at room temperature at least overnight before determining the percent recovery. However, the sodium alginate can be used wet to prepare plastic worms as it is dissolved in water at the start of the procedure. Weigh the sodium alginate and determine the percent recovery from seaweed.

Preparation of plastic worms. Prepare 25 mL of a 2% (w/w) aqueous solution of sodium alginate and 25 mL of 1% (w/w) calcium chloride solution. If colored worms are desired, add a few drops of food coloring to the sodium alginate solution. Add about 5 mL of the calcium chloride solution to a very small beaker or a large test tube. Using a dropper, squirt a few mL of the sodium alginate solution into the calcium solution. Curl the end of a 4 inch piece of copper wire and dip the wire into the solution and attempt to pull out the worms. Record your observations and think about how the calcium ions cross link the alginate polymers.

Additional experiments - work with other students and use sodium alginate with different ionic solutions paying particular attention to the oxidation state of the cation and the success of worm formation.

APPENDIX A.  METAL ALLOYS: Properties, Resources, Data, Information

Links to Information about metal alloys

     Tables of data

        http://www.matweb.com/    http://www.matweb.com/search/PropertySearch.aspx

https://nickelinstitute.org/media/1771/propertiesofsomemetalsandalloys_297_.pdf

https://www.cnclathing.com/guide/metal-strength-chart-mechanical-properties-chart-of-different-metal-grades-and-alloys-cnclathing

https://www.weldinghandbook.com/types-of-metals/

https://www.machinemfg.com/metal-mechanical-properties-chart/

             Resources 

http://www.istl.org/02-spring/internet.html

http://dol1.eng.sunysb.edu/other.html

Information

https://www.qmul.ac.uk/library/library-skills/resource-guides-by-subject/engineering-and-materials-science/useful-websites/

https://www.geeksforgeeks.org/alloys-definition-composition-properties-and-uses/

https://www.compoundchem.com/2015/07/07/alloys/

https://generalscienceias.blogspot.com/2010/12/important-alloys-and-their-contents.html

https://www.visualcapitalist.com/20-common-metal-alloys/

https://www.techglads.com/cse/sem1/properties-alloys/

Predicting properties of alloys

https://news.mit.edu/2020/design-metal-alloys-121

APPENDIX B.  Plastics

Properties

http://www.matweb.com/    http://www.matweb.com/search/PropertySearch.aspx

https://www.curbellplastics.com/Research-Solutions/Plastic-Properties

Information, Links, Teacher Resources

https://en.wikipedia.org/wiki/Plastic

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873019/

http://www.polymer-search.com/covalent/science-teachers-polymer-education-guide.html  

http://agpa.uakron.edu/  

https://pslc.ws/index.htm        http://pslc.ws/macrog/index.htm

https://chem.libretexts.org/Ancillary_Materials/Laboratory_Experiments/Wet_Lab_Experiments/General_Chemistry_Labs/Online_Chemistry_Lab_Manual/Chem_9_Experiments/11% 3A_Synthetic_Polymers_and_Plastics_(Experiment)

Demonstrations, Experiments

https://pslc.ws/index.htm        http://pslc.ws/macrog/index.htm

https://chem.libretexts.org/Ancillary_Materials/Laboratory_Experiments/Wet_Lab_Experiments/General_Chemistry_Labs/Online_Chemistry_Lab_Manual/Chem_9_Experiments/11%3A_Synthetic_Polymers_and_Plastics_(Experiment)

        https://uakron.edu/polymer/agpa-k12outreach/lesson-plans/

        http://www.polymer-search.com/covalent/science-teachers-polymer-education-guide.html

APPENDIX C.  Solutions to Problems.

Table 1.  Composition of alloys

Physical Properties
Table 2.  Properties of brass

Properties of Brass.  For thermal capacity and Modulus of Elasticity (tension), the values for copper and zinc are similar and not surprisingly, the value for brass is also about the same.  For the melting point, the phase diagram shows that copper and zinc have a complex behavior as a function of mixing percentages with the melting point of cartridge brass similar to the melting point of copper but much different than the melting point of zinc. The density of brass is close to a predicted value.  The thermal conductivity and electrical resistivity need to be measured as estimates from copper and zinc give huge errors.  One of the publications on predictions is available online.

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