As the price of silver nitrate increases and chemistry department budgets tighten, the recovery of silver from silver residues of analytical laboratory experiments becomes a necessity rather than a luxury. Although many methods have been proposed, most are complex2 and/or are limited by the anions present in the residue.3 ***7The following recovery procedure was selected, after many experiments, as the most efficient and profitable method. It is based upon the traditional ore refining method of forming the impurities into alow melting slag.Silver residue (a mixture of AgCl, Ag2(CN)2, AgSCN, Agl, AgBr, and Ag2CrOi) was dried in an oven at 110°C until it lost its moist appearance. The oven employed here and the furnace used later in the procedure were hooded because of the toxic reaction products formed from the chloride, thiocyanate, and cyanide ions present in the precipitate. This safety precaution is strongly recommended. If the residue is not predried, the mixture sputters when placed in the furnace. The dried residue was intimately mixed with an equivalent amount of potassium carbonate assuming the residue consists entirely of AgCl. Potassium carbonate, rather than sodium carbonate, was chosen because it forms a slag with a lower melting point. It was determined that the more intimate mixtures of K2C03 and residue gave higher yields. When the ingredients were ground in a ball mill for two hours, we obtained 95% recovery from a silver chloride sample, whereas a casual strirring of the ingredients resulted in only a 60-70% yield.The mixture was placed in a clay crucible and baked in a furnace at 1000°C. At this temperature the reduced silver melts, forming a puddle at the bottom of the crucible. When the reaction is carried out at lowrer temperatures, a sponge-like silver is obtained that has impurities trapped in its porous structure. The crucible is filled no more than three-fourths full as some foaming occurs.The furnace floor was protected by a sheet of asbestors which had been preheated at 1000°C for 2 hr to remove combustibles. The furnace was hooded because COCl2 is formed. The reaction wras considered complete when the temperature had returned to 1000°C.
Within the last decade there has been considerable interest within undergraduate chemistry departments in changing from the traditional course-associated laboratories to a separate and integrated lahoratory program, representing all areas of chemistry. The integrated laboratory cuts across the traditional boundaries of the classical subdivisions of chemistry to allow for experimentation which more closely reflects the interdisciplinary nature of current chemical research. Such a program could also eliminate the sometimes trite and selfcontained exneriments often found in the traditional course-associated laboratory, and students could build a more flexible laboratow exnerience bv choosing among advanced . .experiments in several areas.The role of analvtical chemistrv in a totallv integrated lahoratory is illustrated-by the weli-established proeram at the Massachusetts Institute of Technology. chemistry majors complete four semesters of the integrated laboratorv course which begins the first semester of the second year andconsists of five hours a week in the lahoratory. The following three semesters each require ten hours a week. Associated lectures for two hours a week with each lahoratory course cover discussions of general information and explantions of specific points on each experiment. Although a given group of experiments performed in a prescribed order by every student is required in each course, a variety of experiments is offered from which the student can choose several to comnlete the course.Durlng thr four semesters of lahoratory the students perform 3 w~de selection of both class~cal wet anslgirnl methods and modern instrumental methods. In the first semester, for examole. the following experiments are performed: the equivalent weight of an unknown carhoxylic acid is determined by acid-base titration with a visual indicator and its pK, determined by potentiometric titration; the amount of cholesterol in a crude solid is determined by derivatization and quantitative visible spectroscopy; the yields of various products produced during the acetylation of ferrocene under different conditions are analyzed by quantitative high pressure liquid chromatography; and the analysis of student-prepared tris(ethylenediamine)cobalt(III) chloride is made for both cobalt, by cation exchange and subsequent acid-base titration, and chloride. hv the Faians ~recipitation titration method.From the above listing it is apparent that there need be no lack of analytical methodology in an integrated lahoratory sequence. The question, then, concerns the exact nature of the way analytical chemistry is presented within such a framework. Mere use of a wide selection of analytical techniques is not trainine for a orosoective analvtical chemist nor does it -. . accurately represent what practicing analytical chemists do. Analvtical chemistrv is a orohlem solvine nrocess which has ". a definite pattern involving much more than simply pushing a series of buttons in the correct order and copying a number from a digital readout. Importa...
Das mäßig stabile Radikalanion ON(SO3)22‐ zersetzt sich in DMSO und einigen anderen Lösungsmitteln (wie Pyridin, Acetonitril, CH2Cl2) ziemlich schnell durch einen Prozeß 1. Ordnung, der von einer schnellen Kettenreaktion begleitet wird.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.