Photochemistry: Silver
The photodecomposition of the silver chloride produces silver metal. This demonstration shows a reaction that is important in photography.
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Keywords
applications - practical/real-life, descriptive chemistry, halogens/halides/hydrohalic acids, photochemistry, precipitation reaction, redox reaction, transition elements/metals
Multimedia
Play movie
(QuickTime 3.0 Sorenson, duration 47 seconds, size 3.2 MB)
Silver nitrate solution is poured into a dish containing a piece of filter paper. When sodium chloride solution is added, the paper becomes coated with a layer of solid silver chloride. The paper is moved to another dish, and a key is placed on top of it. When the paper is exposed to the light from a burning magnesium ribbon, the paper darkens due to photodecomposition of the silver chloride, which produces silver metal. Removing the key reveals its image on the paper.
 Sodium chloride solution is added to silver nitrate solution. |
 The paper is moved to another dish and a key is placed on it. |
 The paper is exposed to the light from a burning magnesium ribbon. |
 Removing the key reveals its image on the paper. |
Additional still images for this movie
Discussion
This video demonstrates how photographic film can capture an image. Silver halides can be reduced to metallic silver by light as shown here. When film is exposed to light, each exposed silver halide crystal has a few atoms of silver in it, while unexposed crystals have none. Photographic developer reduces the rest of the silver halide in the exposed crystals, because the reduction occurs faster when there are already silver atoms present. Then a fixer is used to dissolve away the rest of the (unexposed) silver halide. This leaves a negative image--dark where the film has been exposed to light and colorless where it has not been exposed. The processes involved are described in detail in Jacob, A. T., "The Chemistry of Black & White Photography,", Institute for Chemical Education, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396.
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Demonstration Notes, Warnings, Safety Information, etc.
Exam and Quiz Questions
1. What is the white solid formed on the filter paper when sodium chloride solution is poured into the silver nitrate solution?
2. Why is the image of the key not complete? (Part of the smaller end of the key is not visible.)
3. The image produced here is called a "negative" image. Why?