Photochemical Reaction with Thionin

Hazards: 

Sulfuric acid is corrosive

Chemicals and Solutions: 

20 mL 0.001 M Thionin solution (dissolve 0.23 g in 1 L water, prepare fresh)

20 mL of 3M sulfuric acid

Ferrous sulfate: 4g

Prior to presenting the demonstration mix together the following chemicals in a 2 L beaker:

20 mL of 0.001 thionin solution

20 mL 3 M sulfuric acid

sufficient water to bring the volume to 1 L

4 g ferrous sulfate

Materials: 

2L beaker

Aluminum foil

Procedure: 

Place a (thick) piece of aluminum foil on the overhead projector such that half the screen is  covered.

Place the 2 L beaker containing the purple thionin solution on the overhead projector such that half of the beaker is exposed to light and half of the beaker rests on the aluminum foil and is protected from the light.

Turn on the overhead projector.  Any solution exposed to the light will become colorless.

The beaker will have a colorless side and a purple side.  (The reaction can be reversed by turning off the light.)

Hint: 

Discussion: 

"An intense light causes Iron II to reduce thionin in an acidic solution:  the thionin is photochemically reduced.  This demonstration is a visible example of the conversion of light to chemical energy.  The reaction can be reversed by placing the solution in the dark."

 (from Flinn Scientific, Inc., Batavia, IL)

 

To schedule a demonstration, please send an e-mail to the demonstration lab.

 

Contact:

Eric Camp

Lecture Demonstration Technician

Bagley Hall 171

(206) 543-1606

ericcamp@uw.edu

 

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