Analysis of Silver in an Alloy
In this experiment an alloy of silver will be analyzed to determine its silver content. The silver-copper alloy will be dissolved in nitric acid, the silver will be precipitated as silver chloride, and the silver chloride will be filtered, washed, dried and its mass determined. From the mass of the silver chloride formed and the mass of the original sample, you will be able to calculate the percent of silver in the alloy. Because the results are based on the mass of a product, this procedure is classified as a gravimetric analysis.
Silver and copper are very nonreactive metals. Neither will dissolve in hydrochloric acid or sulfuric acid. The "oxidizing" acid nitric acid, HN03, is
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Before adding the sodium chloride solution to the dissolved silver you must rinse any moisture on the bottom of your watch glass back into the beaker of dissolved silver so that way not silver is lost. Thus causing a source of error if not all of the silver ions were still in the beaker upon adding the sodium chloride solution to precipitate the silver as silver chloride. You wash to remove all of the other chemicals from the silver chloride precipitate. There will be copper(II) nitrate, nitric acid and excess sodium chloride. These have to be washed through to make sure only (wet) sodium chloride is left in the filter. The nitric acid in the wash water will not interfere with the weight of the silver chloride because it will be washed through with the filtrate leaving the solid sodium chloride in the filter paper. If the silver chloride is not cool when its mass is determined the calculated percent would be too high, because if we do not dry the precipitate in the oven then the water in the filter paper and solid will affect the weight making it higher. We need for that excess water to be dried out to have a good calculation. We don't use hydrochloric acid to both dissolve and precipitate the silver because the acid cannot dissolve either silver or copper because they are insoluble when mixed. It could work to make a precipitate but not to dissolve the alloy. A special filter crucible rather than plain filter paper is used because