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March 6 2012 3 06 /03 /March /2012 18:17

Silver halides are light sensitive, making them useful for old-time film photography. Silver chloride, a white solid, has the quickest reaction with light. It turns purplish after about one minute in strong sunlight. Upon further exposure, it turns black, as chlorine gas is released (in rates too small to be significant) and silver metal is left behind. Silver bromide, a pale-white solid, reacts after about 15 minutes in strong sunlight. Silver iodide, a yellow solid, hardly reacts with light at all.

 

Silver-halides.JPG Silver-halide-light-exposure.JPG

The first picture shows silver chloride (top), silver bromide (center), and silver iodide (bottom). Unfortunately, the sodium iodide used to produce the silver iodide has ascorbic acid in it, so the silver iodide was reduced to gray silver metal in the second picture. Some yellow silver iodide flakes are visible around the edges of the black puddle. The center pool of AgBr has turned slightly gray. The flakes of silver chloride on the right side of the bottom picture are quite dark gray.

 

Other silver compounds also react with light. Silver nitrate is known to decompose when exposed to light in the presence of organic compounds. Silver carbonate seems to decompose to silver oxide in light, which may further decompose to silver metal. Silver acetate solution slowly decomposes to colloidal silver metal when exposed to sunlight. 8 hours is enough to impart a faint Tyndale effect coloration to a dilute solution of the salt in acetic acid.

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Published by LanthanumK - in Experiments
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