MadSci Network: Chemistry |
Hi Laura, The weight gain is indeed very interesting and is caused by a process known as vulcanization. Charles Goodyear discovered that adding sulfur (in your case sulfuric acid) to rubber made a hard, yet resilient material. As you may recognize from his name, this material eventually became tires (hence Goodyear tires, though not started by Charles Goodyear). What is happening when you the mix the sulfuric acid to the rubber is that the sulfur is "adding" itself to the rubber. Rubber is made up of lots of polymer chains. The additon of sulfur ties these chains together by the formation of sulfur "bridges." These sulfur bridges provide the additional weight you are measuring. The additon of sulfur bridges is a crosslinking technique which can render a material chemically resistant and thermally stable. However, if you had added to much sulfuric acid, you would have crosslinked the rubber so much it would have became brittle. For more details on crosslinking (i.e. vulcanization), check out the following: http://www.psrc.usm.edu/macrog/xlink.htm I hope this helps. Let me know if you need any clarification. KIP
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