A Revision of a General Chemistry Experiment on an Inorganic PolymerizationCondensation Reaction Inorganic polymerization reactions are seldom described in general chemistry textbooks or laboratory manuals. Since most students who take general chemistry are not chemistry majors, but are physical-natural science or engineering majors, they are not aware of inorganic polymers and the vital role they play in industry and science and technology. This is a serious flaw in their education and preparation for their future studies and employment. We have developed a simple and ineroensive exoeriment for general chemistry laboratory. I t requires a simple apparatus and takes no more than 2-3 h. 'Silicates polymerize in acid as follows1
0
I
0-Si-02-
0
I
2N(O-SiOH-)
0
I + H+ + O-SiOH10
I
+ (0-Si-O-Si-O),v
0
I
Washin8 the solid removes the salt hyproducr and prevents reversal of the reaction shown in eq 2. The product is a three-drmenuional solid of high porosity, which, when dry, has a surfacearea 01400-500 milg. (Quartz has a surface area of only 2-3 rm-1g.i A method for comparing the porosities end surface areas of warhed and unwashed product has been determined by lnnea hut ia nor appropriate in conjunctron with this experiment beueure uf the rime and instrumentatiun -~ required. Toa glass beaker add 25 mL of 1M HCI and 25 mL of17% NazSiOa(dermatological h a ~ a r d )eight ; ~ granules of CoCla can he added to note the subsequent water change of the gel aftel. drying. The resulting gel is removed, cut in half, and transferred to two Petri dishes and reweighed. One dish is washed with deionized water until negative to AgN03. This can be accomplished by stirring the gel in a beaker and decanting. The other gel is not treated. Both are placed in a microwave oven an high for 15min and covered with paper to prevent spattering. Alternately, the gels can be heated for 1%h a t 105 'C. The washed and dried silica will be a powder that is 100 times as porous as the unwashed silica, which is a rock. Both dishes will be weighed in 5 min and the students will calculate the number of moles of water ahsorbedlg of silica. This is a good time to explain the commercial preparation of NazSiOa, which is the addition of molten sandand molten NaOH to water. In addition, the role of silica gel as a doped catalyst for petroleum cracking can he discussed. ~
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Suooorted ~~-bv Robert A. Welch Gram $444302. - - 7 7 ~
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'Green. E. E.: Earnmaw. A. ChemisQ olthe Elemems: Pwgamon: New Y a k . 1984: p 397. 2 ime,, W. 6. AmlfliCdlChemkhy 1951, 23. 759 Yomg. J. A . Ed. lmpmving Salary m Me ChemicalL6boratory.A RacticalGnde; W ley: New Yo*. 1987
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Robert J. Palma, Sr. Midwestern State University Wichita Falls. TX 76308
Ed Sargent 49 12 Earl Witchita Falls, TX 76302
614
Journal of Chemical Education
