Purity of Silver Precipitated with Ascorbic Acid At the time of our publication reporting our method for purifying silver by the reduction of the silver diammine complex ion with ascorbic acid', we had an indication that the silver being produced was a t a fair purity, but we had no quantification of its state. Further testing has now shown that our method does, indeed, produce silver a t a high purity. Preliminary analyses were performed on silver produced by our method from solutions of silver nitrate containing 25% of another metal ion. In the cases of silver with nickel, cobalt, cadmium, or zinc, the amounts of impurity metal carried over were in the range of 1-240 ppm (pglg). Copper impurity gave copper in the silver a t the range of about 0.9 to 1.4%.These studies indicated that silver coming from silver chloride could be highly purified by washing the silver chloride precipitate before solution in ammonia, and this would remove almost all other contaminating metal ions. As a test of purity of the silver coming from this procedure, 39 g of a crude silver-bearing metal scrap (silver witb copper, brass, iron, and' other metals) was digested in minimum-volume nitric acid. The solution was handled by our reported method1, witb both the silver chloride crystal and the precipitated silver powder being very thoroughly washed with deionized distilled water. The silver powder thus produced (19 g) was melted, then a sample was analyzed by dc plasma emission spectrbscopy. Analysis showed copper at 0.044 ppm, iron a t 0.030 ppm, zinc at 0.028 ppm, and nickel at 0.016 ppm. Arsenic, cobalt, cadmium, manganese, lead, and chromium were below limits of detection of the instrument. These results indicate that if the only impurities were the ones we sampled, the 10 impurity metals quantitated would add to a total of no more than 0.20 ppm. However, by summing the actual amounts of those metals (Zn, Fe, Cu, Nil that would mast likely be present above their limits of quantitation by the method used, we see a total of 0.118 ppm impurity. We realize that silver orobablv does not eaual the remainder of the mass oresent. hut if it were so considered, this would represent silver of purity greater than 6N5, (less than I pprn irnpurit).l. Thus, we recommend the consideration ofour mrthod if silver uf blah purity ixneeded. Likewise, if the prerlpitater are well washed, there is no reason to question the usr of the sliver ar hrmg "equal to reagent grade" and surtat,le fur any laboratory uses, both qualitative and quantitative. Acknowledgment We express deep appreciation for the assistance given us by William Fateley, Robert Fry, and Donovan Miller of the Kansas State University Chemistry Department.
I
Hill, James W.: Bellows, Lena. J. Chem. Educ. 1986, 63,357 Person to whom communications may be addressed. James W. Hill2 and Max Crocker Panhandle State University Goodwell. OK 73939
Volume 65
Number 1
January 1988
87
