March 2018

# Growing copper crystals

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Yvonne Clifford, 2015 winner of the Chemical Institute of Canada Beaumier Award, Jacob Hespeler Secondary School, Cambridge, Ontario

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I have been fortunate to have attended two ASM Material Camps for educators.1 I knew after having attended the first day of Part 1 that I would be starting my new school year with a copious amount of relevant material. The material was presented in such a manner that I could easily go back to my classes and add to my repertoire. Following are but a few specific examples of what I implemented into my chemistry courses. I added these labs to grade 11 chemistry:

• work hardening a copper wire
• an inquiry lab on the activity series,
• pop cans and acid, and
• split a penny.

These labs correspond to the Ontario Chemistry Curriculum. The students learned to apply the chemistry theory in a hands-on format. My goal as the primary chemistry teacher at JHSS is not only to educate the students specifically assigned to me but anyone in the school. The pop can in acid lab, for example, was so engaging that I had scores of other people going through my room to see what my students had been working on.

In grade 12 chemistry, I added the following:

- the factors that affect corrosion using simple chemicals such as hydrogen peroxide, water, salt and nails,
- heat-treating steel,
- electroplating,
- making batteries, and
- an entire class on polymers.

I would, say however, that I have incorporated (without exaggerating) at least 100 new ideas, labs, stories or demonstrations. One particular component that I constantly try to do as a chemistry teacher is to make theoretical chemistry relevant to the everyday world. The ASM Material Camps have allowed me to not just do this but to do so with confidence. Part 2 of the ASM Material Camp reinforced and greatly enhanced the material I learned in Part 1. More was expected of us as we didn’t just “do” the labs but learned how to “set-up” the labs. Part 1 was like drinking from a fire hydrant (so much great information at one time); Part 2 allowed time to slow down a bit and process all the wonderful information from Part 1. The following is just one of the labs that I have adapted from the ASM Material Camps for Educators.

## Growing copper crystals2,3

This is a simple, but colourful, redox reaction (see front cover). Copper(II) sulfate reacts with iron. Cotton is used to separate the reactants with a nifty layering effect in the final product. Students will be able to watch the products form over a couple of days. The solid copper product is quite beautiful once it is removed and washed.

You could use this for reaction types, redox or even just an activity to encourage good observations over several days. Since I have introduced this lab, it has become a student favorite. It can be pointed out that this reaction simulates how pure mineral copper deposits in Earth’s crust.2

### Materials

Large test tube and stopper (or soda bottle preform), cotton pads, non-iodized salt, copper(II) sulfate pentahydrate, three iron nails, sand paper, scoopula/ spoon, tweezers, plastic stirring rod, 250 mL beaker, watch glass, disposable pipette.

#### Procedure

1. Cut out two round pieces of cotton the size of the test tube opening. Soak both in tap water.
2. Using sandpaper remove any rust from the three nails.
3. Using masking tape label the large test tube (name and contents).
4. Using a scoopula/spoon place approximately 2 to 3 cm of copper(II) sulfate pentahydrate crystals into the large test tube. Any excess place in INORGANIC waste pail.
5. Using a 250 mL beaker, gently add tap water to just cover the copper(II) sulfate pentahydrate. Place one of the water-soaked cut-out cotton pads gently on top of the copper(II) sulfate. Use a stirring rod to push it gently into place.
6. Using a scoopula/spoon gently place approximately 1 to 2 cm of non-iodized salt into the large test tube.
7. Gently cover the salt layer with tap water. Pour slowly and gently to avoid stirring or mixing the layers.
8. Add the second small piece of wet cotton pad as a barrier layer.
9. Gently place three nails on top of the second barrier. Gently add water to cover the nails. Cap the test tube. Take a photo of test tube and record all observations.
10. Place the capped test tube in the test tube rack.
11. Make observations every day for 7 days both written and with a camera. (see Elora Yott’s photos below)
12. Before cleaning up show the instructor the copper crystals.
13. Clean-up the test tube by slowly pouring the test tube contents into a waste beaker.
14. Label a watch glass and carefully separate the copper from the other solids using a scoopula/tweezers. Lay the copper on a watch glass.
15. Gently rinse the copper with water using an eye dropper/disposable pipette.
16. Remove as much water as possible and then place in the drying oven overnight.
17. Dispose of all waste in the INORGANIC black pail.

Setup with layering of copper(II) sulfate (bottom), cotton, salt and three nails in water.

Two days later. The products can be observed — dark green substance is likely a copper complex formed with chloride ions.

Reaction after several days. At the end of the reaction, the green coloured material is not present

#### References

1. A free week-long, hands-on lab experience shows educators how to use applied engineering techniques in their classroom. ASM Teachers Camp is an idea-generating workshop introducing teachers to methods that make math and core science principles more enticing and relevant to their middle and high school students. Over 30 camps are run across the US and Canada. Find the schedule online. Applicants are admitted to the program on a first-come-first-served basis. www.asmfoundation.org/who-we-impact/teachers/teacher-materials/

2. Original lab: J. Cortez, D. Powell and E. Mellon, Test tube geology: A slowly developing redox system for class study, Journal of Chemical Education, April 1988, pages 350-351

3. www.asmfoundation.org/wp-content/uploads/2017/10/MATERIALS-MATTER-CURRICULUM-15-hours.pdf

#### Comments

We asked Chris Miedema, Ashbury College, Ottawa, Ontario to comment on this lab. He suggested and presents this workshop activity at ASM Material Camps.

When I present this activity I stress the geology in a test tube. The bottom layer represents the copper mineralization that is found in late-stage of oxidation zones of copper deposits as the mineral named chalcanthite. This mineral is not common on the surface, because a good storm washes it away! Then the salt layer represents evaporated sea water, forming a halite (NaCl) deposit. The nail (Fe) represents a volcanic eruption. I try to impress on the kids how long it takes for this to actually happen in real time, as all these minerals are solids! I discuss the native copper deposits in Michigan as an example. It is a very good lab to get kids to predict the reaction by applying their knowledge of redox chemistry.

Chris also sent in the February 2017 cover photo of native copper and silver nugget.

#### Additional resources

A nice diagram of the setup can be found at Department of Materials Science and Engineering, University of Illinois Urbana-Champaign . In this version small circles of filter papers are used to separate the layers instead of the cotton pads. http://matse1.matse.illinois.edu/metals/i.html

North Carolina School of Science and Mathematics Distance Ed has two 2-minute YouTube videos, www.dlt.ncssm.edu.

Part 1 shows setup,

Watch video on YouTube
Part 2 shows the final products of the reaction,
Watch video on YouTube
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