Public Lab Research note


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Hydrogen Sulfide tarnishing Silver

by Sara |

http://www.finishing.com/204/32.shtml

Research question can we use silver tarnishing as a proxy for hydrogen sulfide monitoring?

"silver, metallic chemical element; symbol Ag [Lat. argentum]; at. no. 47; at. wt. 107.8682; m.p. 961.93°C;; b.p. 2,212°C;; sp. gr. 10.5 at 20°C;; valence +1 or +2. Pure silver is nearly white, lustrous, soft, very ductile, malleable, and an excellent conductor of heat and electricity. In many of its properties it resembles copper and gold, the elements above and below it in Group 11 of the periodic table. It is not a chemically active metal, being considerably below hydrogen in the electromotive series (see metal). It is, however, attacked by nitric acid (forming the nitrate) and by hot concentrated sulfuric acid. Silver is almost always monovalent in its compounds, but an oxide, a fluoride, and a sulfide of divalent silver are known. It does not oxidize in air but reacts with the hydrogen sulfide present in the air, forming silver sulfide (tarnish). Silver nitrate is the most important compound." from: http://encyclopedia2.thefreedictionary.com/Ammoniacal+silver+nitrate

Chlorine also tarnishes silver. http://www.emeraldinsight.com/journals.htm?articleid=1589027&show=abstract

"Silver will react with extremely low levels of hydrogen sulphide. However, the gas is so pungent that it is difficult to withstand more than 5-10 ppm of the gas - if this gets exceeded you can become desensitised and not smell it at all; this is when it kills you! You will be aware that silver will go black in an atmosphere where you cannot smell hydrogen sulphide, so the minimum level will be in the ppb or even ppt range; however, the detection of the reaction will be dependent on how long the silver is exposed to the gas. The rate of reaction will also be dependent on the relative humidity of the air, as the water is needed to dissolve the gas. Hydrogen sulphide and silver react to form black silver sulphide, one of the most insoluble salts of silver and this is what causes the tarnish. However, it can be very easily reduced by putting it in a dilute solution of sodium carbonate and attaching a piece of aluminium foil to the article. Flourescent lights do produce some UV light, depending on the filler gas, but commercially available domestic or general purpose industrial lights do not constitute a UV health hazard."

Mat L asked could photographic film be used monitor Hydrogen Sulfide?:

http://www.electrochem.org/dl/ma/199/pdfs/0148.pdf



hydrogen-sulfide-sensing hydrogen-sulfide h2s silver chlorene

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