Materials Included In Kit

Additional Materials Required

Prelab Preparation

Make fresh the day of the lab. Note: Solutions may be made ahead of time if stored in a dark bottle
away from light. The recipe provides enough solution for 30 students working individually.

1. To make 1 liter of ferric ammonia citrate solution, add 220 g of ferric ammonium citrate to 1000 mL of distilled or deionized water. Stir to dissolve. Note: This process will need to be repeated four times to obtain a total of 5 liters of solution (five batches of 1000 mL each) required for 30 students.
2. To make 1 liter of potassium ferricyanide solution, add 110 g of potassium ferricyanide to 1000 mL of distilled or deionized water. Stir to dissolve. Note: This process will need to be repeated four times to obtain a total of 5 liters of solution (five batches of 1000 mL each) required for 30 students.

Safety Precautions

The combined Prussian blue solution will dye the skin a dark blue. The Prussian blue solution is nontoxic; its color will fade with time. Dangerous hydrogen cyanide gas may result when potassium ferricyanide is heated or placed in contact with strong acid. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Have students wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Dispose of ferric ammonium sulfate according to Flinn Suggested Disposal Method #26a. Dispose of potassium ferricyanide solution according to Flinn Suggested Disposal Method #14. The soaking solution may be disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough chemicals are provided in this kit for 30 students. This laboratory activity can reasonably be completed in parts of two 50-minute class periods.
• Ferric ammonium citrate is a complex salt of undetermined structure. It is composed of 16.5–18.5% iron, 9% ammonia and 65% citric acid.
• The T-shirts can be developed while still damp. Dry T-shirts produce a darker and more permanent blue color than those that are still moist and are also easier to manipulate. If drying the shirts overnight, select a room that can be darkened and where a pole can be placed to hang the shirts. Be sure to place absorbents or a drop cloth under the T-shirts to collect any drips.
• Any object that blocks the sun even partially will work. Photos and images can be printed and copied on overhead transparency. When the shirt is developed, the image appears as a negative.
• You may want to try the procedure on cotton squares before the student lab. This will give you a good feel for the overall process before the students attempt it.
• The cardboard insert creates a flat surface for placing objects on the T-shirt. It also prevents UV light from filtering through the back of the material and developing the areas on the front.
• As an alternative, areas of the shirt can be “painted” with the two solutions. Only that section of the shirt will turn blue.
• Remind students to wear their gloves when handling the shirts.
• Perform this lab procedure on a day when the students will be able to develop their images outside. A sunny day will provide for the fastest developing of the images; however, an overcast day will set the stage for additional discussion of ultraviolet radiation. Consider having students develop one print in a sunny area and one in a cloudy or shaded area. Compare the results. Have students try translucent objects.
• If your situation prohibits students from going outside, try developing the T-shirts using an artificial ultraviolet “black” light.
• When actual blueprints are made, instead of objects being place directly on the paper, a sketch is drawn on colorless plastic and then placed over the blueprint paper before being exposed to UV light. The drawing forms white lines on the paper, which prevent the transmission of UV light and therefore does not expose the photographic chemical in those areas.
• Plastic tubs can be shared, with students combining their soaking solutions and T-shirts. One liter of soaking solution will treat three T-shirts.
• Treated shirts should be washed using liquid laundry soaps or dish soaps. Powdered detergents can turn the blueprint to yellow.

Further Extensions

• Test various sunscreens and determine the effectiveness in blocking UV rays. (Try Flinn’s FB1561 Sun Protection Factor Kit.)
• Use black-and-white negatives to produce an image on the blueprint T-shirts.

Answers to Questions

1. Why is it best to store ferric ammonium citrate and other photographic chemicals in brown or dark-colored bottles?

   The brown bottles help filter out UV light, extending the life of the chemical.

2. Why does the lab work on overcast days as well as on clear days?

   Ultraviolet radiation can and does penetrate the clouds.

3. Why doesn’t incandescent light (classroom lighting) develop the T-shirts?

   Higher energy ultraviolet rays (which are not present in incandescent bulbs) are needed to develop the print.

4. Explain why blueprints or photographs may slowly deteriorate if they have not been rinsed well during development.

   Unreacted chemicals left on the paper will react with the light, ruining the image on the print.

5. Where is the best place for storing photographs? What would you predict sunlight would do to photographs? Why?

   Photographs are best stored in a dark area out of the sunlight. Sunlight would gradually lighten the image causing it to fade.

6. (Optional) Compare the reduction potentials for silver ion and iron(II) or iron(III) ions. Which metal is more likely to be reduced and therefore produce insoluble deposits on film? What other metal salts might also work well for photography?

   Silver ion, Ag⁺, is more easily reduced to the solid than iron, either Fe²⁺ or Fe³⁺ ion (E^o_red = 0.7996 V for silver versus –0.447 V and –0.037 V, for iron(II) and iron(III), respectively). Gold has a higher reduction potential than silver (E^o_red = 1.498 V), but its high cost keeps it from being used as an alternative to silver in photographic processes.

Introduction

Make your own UV-sensitive T-shirt and develop images of any object or pattern that you want! Take advantage of the ultraviolet-activated chemical reaction used in blueprinting to produce permanent images on the T-shirt.

Concepts

• Light-activated reactions
• Photochemistry
• Ultraviolet (UV) light

Background

Photochemical reactions are chemical changes caused by light. Many important reactions are photochemical. Ozone, O₃, in the upper atmosphere reacts with ultraviolet light to form an oxygen molecule, O₂, and atomic oxygen, O. In this way, ozone reduces the amount of harmful UV radiation that reaches the earth. Photosynthesis is another important photochemical reaction. Plants and bacteria produce carbohydrates from the reaction of light with carbon dioxide and water.

The preparation of UV-sensitive cloth involves the combination of two iron salts—ferric ammonium citrate and potassium ferricyanide, K₃Fe(CN)₆.

Exposing cloth that has been soaked in a ferric ammonium citrate and potassium ferricyanide solution to UV light results in a reduction of iron(III) (Fe³⁺) ions to iron(II), Fe²⁺.

Iron(II) ions combine with hexacyanoferrate(III) ion from the potassium ferricyanide, resulting in the characteristic dark blue color of the exposed part of a blueprint. The dark blue color is due to a mixed ferrous–ferric [iron(II)–iron(III)] compound, Fe₄[Fe(CN)₆]₃•H₂O. In the areas where the cloth is covered by an opaque object (and protected from UV light), this reaction does not occur and the cloth remains its original color.

The overall reaction is

where Prussian blue = Fe₄[Fe(CN)₆]₃•H₂O

The resulting Fe²⁺ ions react with hexacyanoferrate(III) ions to produce Turnbull’s blue, also known as Prussian blue.

Prussian blue and Turnbull’s blue have been shown by X-ray crystallography to be the same compound. It is a mixed iron(II)–iron(III) compound that is best described as “ferric ferrocyanide,” with the formula Fe₄[Fe(CN)₆]₃. The structure consists of a cubic array of iron ions with cyanide ions along the cube edges and water molecules in the cubes.

The general principle involved in making UV-sensitive T-shirts is similar to that used in the photographic process. Instead of iron salts, black and white photography uses silver salts coated on cellulose acetate paper. Silver is easily and quickly reduced from Ag⁺ to Ag(s) when exposed to light. When film is exposed to light, the areas exposed to the most light form the most silver atoms and thus appear black on the negative. Areas that have not been exposed to light appear white on the negative because no silver ions have been reduced. The fixing and washing processes remove the excess reactants, preventing further darkening of the negative. Producing a black and white photograph from the negative involves shining light through the negative onto a fresh sheet of photosensitive paper.

Experiment Overview

Today’s experiment involves two parts. In Part A, a UV-sensitive T-shirts will be prepared by soaking the shirt in a bath of the two iron salts. In Part B, the treated T-shirts will then be exposed to ultraviolet radiation. Be creative and experiment with placing a variety of different objects—opaque and translucent—on the T-shirt. Try exposing the T-shirts under different conditions and with differing degrees of brightness (e.g., sunny, in the shade) to determine the amount of ultraviolet radiation present.

Materials

Prelab Questions

1. Collect various objects and patterns to be placed on the T-shirts. Opaque or translucent objects work well.
2. Cut out a piece of cardboard that will fit inside the T-shirt top to bottom.

Safety Precautions

The combined Prussian blue solution will dye the skin a dark blue. The Prussian blue solution is nontoxic; its color will fade with time. Dangerous hydrogen cyanide gas may result when potassium ferricyanide is heated or placed in contact with strong acid. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part A. Preparing a UV-Sensitive T-shirt

1. Use a 250-mL graduated cylinder to obtain 160 mL of the ferric ammonium citrate solution. Pour the solution into the plastic tub.
2. Use the same 250-mL graduated cylinder to obtain 160 mL of the potassium ferricyanide solution. Pour this into the plastic tub. Stir the solution well with the stirring rod.
3. Place the T-shirt in the solution in the tub. Mix the solution with a stirring rod to ensure the T-shirt is wetted completely through. Let the T-shirt soak for several minutes.
4. Set out paper towels or newspapers on the lab bench for the T-shirt.
5. With gloves on, remove the T-shirt from the solution and wring the excess solution out, doing this over the soaking tub. Spread out the T-shirt on the paper towels.
6. Place the T-shirt on a hanger. Place the T-shirt in a dark room to dry overnight.
7. Dispose of the soaking solution as directed by the instructor.

8. Remove the dried T-shirt from the hanger and place it in a black plastic bag.
9. Locate both a sunny area and a cloudy or shaded area outside.
10. Bring objects and patterns, cardboard insert and the treated T-shirt into the shaded area. Remove the T-shirt from the bag, place the cardboard sheet inside the T-shirt and quickly place the object(s) or pattern on the T-shirt. Note: Doing this in the shade helps to block the T-shirt from direct sunlight.
11. With the object sitting on the treated T-shirt, move to a sunny area. Set the T-shirt in the sunlight, exposing it to bright, direct sunlight until the T-shirt turns a dark blue color. This step will take about 20 minutes on each side, depending on the brightness of the sunlight.)
12. After the T-shirt is developed, remove the objects and place the T-shirt back in the plastic bag. Bring it indoors (out of the sunlight). Wearing gloves and holding the T-shirt with tongs, rinse it under cold water for a few minutes to remove the yellow color of excess iron(III) ions. Rinse until the solution turns clear and the T-shirt turns a lighter shade of blue.

Student Worksheet PDF

12785_Student1.pdf