Blueprint making with UV (ultraviolet) changing

Molly Mattias Chelsea High School 740 N Freer Road Chelsea MI 48118

I was looking for a hands-on activity for the unit in my senior to the soaking from the dye but I had the students chemistry class that covered material on electromagnetic cut the poster board in half to reduce the amount of radiation. In this unit we discuss ideas such as wavelengths, chemicals needed to cover the paper. visible light, and line spectra. After a few days of class I used the activity to create posters for my classroom. Paul discussion my students really needed a chance to get out of Groves and Kathy Kitzman have their students transfer this their seats and put their hands on something, yet these ideas template to a t-shirt so that students can wear it.2 are submicroscopic. I had not found lab activities other than the traditional flame tests. My class is an advanced elective class 2. Students created the template from an ordinary piece of whose content closely follows that of an AP chemistry paper and secured it to their white poster board. I just used curriculum so these students have done these traditional the paper we use in our copy machines. activities. Blueprint making with UV is a great addition to break up the calculations we had been doing. 3. We took the boards outside and, with the class and myself

wearing goggles, I used a spray bottle to spray the boards Students really took an interest in their design template. I had with the dye . See the recipe and directions below. them create a simple design we could hang in our classroom during the winter holiday season. They enjoyed having a I tried to spray the entire board evenly. It will be yellow as it chance to be creative and having another opportunity to watch goes on and as the reaction proceeds it will turn blue. chemistry happen. 4. The solution takes approximately 15 minutes to “develop” What it does from yellow to blue. Depending on the level of the students, other activities might be needed to occupy this time so they ∙ When the two chemicals, aqueous solutions of ferric are not just standing around. I used this activity as a quick ammonium citrate and , are mixed, “hands-on” in my advanced chemistry class so I spoke to the resulting solution will turn from yellow to blue when them about the reaction taking place while we were standing exposed to sunlight. Paper is sprayed with this solution. outside waiting. If the material is not exposed to the sunlight it will remain yellow. 5. After the color change occurred we took the boards into the classroom and we let them dry on top of the lab benches ∙ The ultraviolet radiation from the sunlight catalyzes the until the next day. Students then removed the template and reaction. This reaction represents the process the unexposed area had remained white. originally used to make blueprints. As it is the UV light that is the catalyst, a UV light source other than sunlight is easily Problems to keep in mind substituted in the procedure. ∙ I did not give students individual spray bottles because this ∙ It is the ferric ammonium citrate that is the photosensitive can be messy and stain fingers and clothes. component in the process. to UV light reduces the Fe(III) to Fe(II) with the electron donor being citrate. The ∙ Students really have to “seal” their paper template. Fe(II) complexes with the ferricyanide ion, with subsequent Otherwise, the dye will run behind their template in areas electron transfer, to form insoluble ferric — and leave it streaked with yellow. (III) hexacyanoferrate(II), or . There is some uncertainty with the structure of Prussian Blue ∙ One student used tape to write out a word. It kept the resulting in the chemical reactions not being well understood.1 solution off the poster board but then you’re left with tape on the paper. But maybe “post-it” notes might work or using the ∙ Prussian Blue is practically insoluble in water and has been “removable glue” type glue sticks to attach the template and used for printing in paint pigment, typewriter ribbon and then remove when the paper is dry. paper.1 ∙ The other references solved this streaking problem by The procedure spraying the paper/t-shirt prior to securing the template then exposing to the UV source. Keep in mind then the area 1. Students create a design template to be used on a piece of behind the template will be yellow and not white but at least poster board. Poster board was sturdy enough to stand up it is not streaked. February 2007/Chem 13 News 5

• Once the design template is removed from the paper/t- Chemical in the news (continued from page 1) shirt yellow solution that has gotten behind the template will gradually turn blue as it is exposed to ∙ 210Po must be ingested in order to kill. It can be handled small doses of UV light coming through the windows. safely if it is in a container since a barrier as thin as a sheet Rinsing the paper/t-shirt as described in the references of paper or plastic will not allow the alpha particles to pass.1

will remove as much unexposed dye as possible so ∙ On a mass basis, 210Po is about a million times as toxic as that the entire surface does not end up blue. HCN. See student activity #3 below.

210 I made 100 mL of the “developing solution” according to the ∙ Po has been used as a heat source to power thermo- directions below. I had twenty-five students create a design on electric generators; as a neutron source by alloying it with a piece of 8x10 poster board and this was not quite enough. I bismuth, which absorbs the alpha particle and emits a had to make an extra 100 mL. Other references used slightly neutron; and as a static eliminator (alloyed with gold, for 4 different amounts of each chemical but I found this recipe to example, for safety) in textile mills. work well. Possible student activities

I found this in a few locations on the internet and have to give 210 big credit to Paul Groves at www.chemmybear.com and Kathy 1. Write the nuclear equation for the decay of 84 Po to lead, with the emission of an alpha particle. Kitzman at Mercy High School Farmington Hills, MI (who is also referenced at this website). I first found it at chemmybear.com 2. Consult the Chemical Rubber Company Handbook of with pictures of the students doing the activity along with recipes Chemistry and Physics to find out whether this isotope of for the solutions. Kathy Kitzman was very helpful with lead is stable, and if so, what percent it represents of pure alternative recipes for the developing solution that I have used in lead. my classroom. I also received much needed advice from other 3. The 1982-83 edition of the CRC Handbook (reference 3 teachers who are a part of SEMTCO (South Eastern Michigan below) says that 210Po is 2.5 x 1011 more poisonous than Chemistry Teachers’ Organization). A version of this activity HCN on a mass basis — nearly a trillion-fold (1012). This can also be found in the Journal of Chemical Education, seems to be wrong. Other sources state that the factor is September 1999 as a JCE Classroom insert. More clarification only one million (106). What does your edition of the CRC 1 of the chemical reactions can also be found in the same issue. Handbook say? By googling the internet, can you find other sources that compare the lethal doses of 210Po and HCN? Recipe page What do they say? Which value should you trust, and why?

210 I made solution A and solution B separately and did not combine 4. What is the rate constant for the decay of Po, given a half-life of 138.39 days? them until one hour prior to the activity. (The UV light source is -kt needed to catalyze the reaction but I did not want the reaction to 5. The integrated rate law for nuclear decay is N = N0 e , happen any earlier than necessary.) where N is the number of atoms remaining at time t, and N0 is the number to start with. In one gram of polonium atoms, To make 2 L of developing solution: how many atoms decay in the first second?

-13 Solution A: 240 g of ferric ammonium citrate in 1.0 L of solution 6. 1 MeV (million electron volts) is equivalent to 1.6 x 10 J.

How much energy is released in one second from one gram Solution B: 120 g of potassium ferricyanide in 1.0 L of solution of pure 210Po (see question 5), given that each decay re-

leases 5.3 MeV? Does this agree with the statement above To make 100 mL of developing solution: that 210Po releases energy at the rate of about 140 W/g? Solution A: 12 g of ferric ammonium citrate in 50 mL of solution (Remember that 1 watt (W) equals 1 joule per second.) Solution B: 6 g of potassium ferricyanide in 50 mL of solution Questions 3, 5 and 6 are fairly challenging. Answers will be References provided next month.

1. G. Lawrence and S. Fishelson, Journal of Chemical References

Education, September 1999, Volume 76, page 1199-1200, 1. Los Angeles Times, “Polonium-210’s quiet trail of death”, 1216A-1216B January 1, 2007. (Find it by googling on ‘latimes polonium’) 2. www.chemmybear.com ∎ 2. nobelprize.org/nobel_prizes/chemistry/laureates/1911/index.html 3. CRC Handbook, 63rd edition, 1982-83, Chemical Rubber Company, pages B31-32.

4. Wikipedia Encyclopedia,

http://en.wikipedia.org/wiki/Polonium. ∎

6 Chem 13 News/February 2007