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Chemistry and Crayola

Tom Kuntzleman's picture
Wed, 03/13/2013 - 12:54 -- Tom Kuntzleman

Have you seen the new Crayola Crystal Effects Window Markers? You can draw on windows with these markers. Better yet, you can use these markers to teach students some chemistry! After drawing on a window with these markers and waiting a little while, the marker ink appears to crystalize! Check out the video below to see how they work.

I bought some of these for my three sons (they're in 4th, 6th and 8th grade) and they had all kinds of fun using them to draw on the bathroom mirror. Even my college students find these markers interesting. In fact, I first became aware of these markers when two of my upper level chemistry students came by my office one day to ask me how they worked. I had never seen the markers before, but as I watched the marker ink crystalize, I was immediately reminded of a familiar chemistry demonstration: The crystallization of a supersaturated solution of sodium acetate. Sodium acetate is a weak base that can be formed from the reaction between the strong acid sodium hydroxide and the weak acid acetic acid:

NaOH + CH3COOH --> HOH + CH3COONa

Check out the video below to see the crystallization of sodium acetate from a supersaturated solution (skip to 0:57 in the video to skip an explanation of how to prepare the solution).

The similarities I observed between the crystallization of the marker ink and the supersaturated sodium acetate solution made me wonder if the markers contain supersaturated sodium acetate. So I headed into the lab with some of my students to do some experiments to test this idea. Below is a video of one of the experiments that we tried.

We’ve been working on quite a few more experiments on these markers to see if sodium acetate is present in the marker ink. One of my students will be working with these markers for her required small research project in my General Chemistry class. If you have the time, we’d sure appreciate it if you would comment with some ideas of experiments we might try.

The two references below describe how to prepare supersaturated sodium acetate solutions. These two references also describe some interesting experiments with these solutions.

Jamil Ahmad J. Chem. Educ., 2000, 77, p. 1446.

Gene A. Hiegel J. Chem. Educ., 1980, 57, p. 152.

Comments

Submitted by Marsilio Langella on

If you added dropwise a 1 M silver nitrate solution to the two beakers would you get the formation of silver acetate. This would confirm the acetate in the unknown. The solubility of silver acetate is

Silver Acetate at 25 degrees C 11.11g/L Ksp 2.0 x 10-3

Marsilio ( Mark) Langella
Colllege Board AP Chemistry Consultant
AP Chemistry Instructor , Mahopac HS

Tom Kuntzleman's picture
Submitted by Tom Kuntzleman on

Mark:

I tried your experiment today.  As you suggested, I added 1 M Ag+ to the marker residue and saw no precipitate.  This of course suggests the markers do not contain acetate.  When running controls, however, I noticed that a quite concentrated sample of acetate was required to cause precipitation.  This is likely due to the relatively large ksp of silver acetate you report.  Before completely ruling out acetate as a component of the marker, I think we'll try collecting a large amount of marker residue to get a concentrated sample to test.

I have noticed that the marker residue, when dissolved in water, causes the water to become bubbly.  Kind of detergent-like.  This makes me wonder if the residue contains a long chain carboxylate.  Anyway, you have certainly given me a lot of ideas to test.  I'll pass these ideas on to my general chemistry student who will be studying these markers for her small research project.  Thanks so much for your suggested experiment, and let me know if you learn anything about these markers when experimenting with them in the lab!

Tom Kuntzleman

Tom Kuntzleman's picture
Submitted by Tom Kuntzleman on

 

I had two of my students, Nathan Ford and Kristen Rohrer, test the markers for acetate in the following way:  They cut open a colorless marker to reveal the inner felt core.  Using gloves, the felt core was squeezed to collect the liquid contents in the felt.  It was noticed that the liquid was slightly foamy.  They were able to collect perhaps 2- 3 mL of fluid, which was set aside in a sealed flask.  After four days, no crystallization was observed in the marker fluid extract.  Next, one drop of the marker extract was mixed with 1 drop of 1 M AgNO3.  A very faint, white precipitate was observed, consistent with the presence of acetate.    

 The Ksp of silver acetate is 0.002, so in a mixture with a silver concentration on the order of 1 M, an acetate concentration of greater than 0.002 M will be necessary to precipitate the acetate:

Ksp = [silver ion][acetate ion]

0.002 = (1 M)[acetate ion]

0.002 M = [acetate ion]

The procedure I tried before probably diluted any acetate in the markers to lower than 0.002 M, so I observed no precipitate.  (Previously, I drew on a glass plate with the markers.  Next, the marker residue was rinsed with deionized water into a beaker).  In Nathan and Kristen’s procedure, the marker contents were collected straight from the marker in an attempt to keep the acetate concentration high enough to precipitate.  It looks like their procedure worked.

A million thanks to Marsilio Langella for suggesting this experiment!

 

Tom Kuntzleman

Tom Kuntzleman's picture
Submitted by Tom Kuntzleman on

Hi Mark:

 

This is a great suggestion.  I'll be sure to try it when I head to the lab tomorrow.  I willl let you know how it turns out.  Thanks so much!

 

Tom Kuntzleman

Submitted by Marsilio Langella on

I wonder when you write on the surface does the surface temperature change significantly that it could be detected by a surface thermometer. If it is a supersaturated solution then crystal formation would be exothermic and we should be able to detect the energy release. I  purchased some markers this week. I think this product could have some cool lab and demo potential. Thank you for sharing.

Marsilio ( Mark) Langella
Colllege Board AP Chemistry Consultant
AP Chemistry Instructor , Mahopac HS

Tom Kuntzleman's picture
Submitted by Tom Kuntzleman on

Hi Marsilio

I've tried this experiment, but haven't been able to get conclusive results.  I connect a thermistor to a data acquisition system to collect temperature vs. time data. Next, I draw directly on the thermistor surface with the crystal marker.  I see an initial drop in temperature, which I interpret as liquid contents of the marker evaporating off the surface of the thermistor.  After this initial drop, an increase in temperature is observed.  However, when I try the same experiment with a normal marker, the same effect is observed.  Perhaps there isn't enough crystal formation on the thermistor surface to get a large enough temperature increase to observe.  

I think the next thing to try is to cut the marker open and remove the felt plug in the marker.  We'll collect a large amount of the liquid contents of the crystal marker by squeezing the felt plug.  I'll then tape a thermistor to a flat surface, and pour the liquid marker contents on top of the thermistor.  I'll collect temperature vs. time data, and wait until I observe crystallization.  What do you think of this idea?  Do you have any other suggestions on how to detect the exothermic change?

Tom Kuntzleman

Submitted by Ramona Caswell on

I'm not sure how this would work, but reading these last two ideas made me think of using a temperature sensitive surface.  I have some plastic sheet liquid crystals that change color at different temperatures (sort of like mood rings).  Some of these change at 20-25, others between 30-35.  If you want to see that it is exothermic, could you write with the markers on a sheet of liquid crystal and watch the color change as it crystalizes?  This wouldn't be very quantitative, but it could possibly show the exothermic crystalization and it would be possible to quatify the color of the plastic to the temperature.

Tom Kuntzleman's picture
Submitted by Tom Kuntzleman on

Hi Ramona:

I tried using the crystal markers to draw on the plastic sheet liquid crystals.  I had one sheet that changed at 20-25oC, another at 25-30oC, and a third that changed at 30-35oC.  I saw no color change on any of the sheets at all.  I also tried temperature senstive paper and pencils that had a temperature sensitive surface.  No luck.  I think the amount of material that is crystallizing is too small to cause any perceptible change on these materials.  Bummer!  I think next I'm going to try collecting a large amount of liquid material from one of the markers and dump it on some of these materials.  

Tom Kuntzleman

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Submitted by Tom Kuntzleman on

Hi Ramona

This is a great idea!  I found some heat sensitive paper at this link, and some heat sensitive pencils here.  I also found some plastic that might work for what you are suggesting.  I'll let you know how things work out.  Thank you so much for this suggestion.  

Tom

Tom Kuntzleman