the nitric acid will not interfere with your analysis to
find the mass of silver in the alloy.
Some of the nitric
acid is used to oxidize the Ag and Cu to their +1 and +2 states respectively, forming
nitrate salts with each of the metal ions. The nitrate ions that oxidize the metals are
reduced to NO (g).
When the NaCl is added the silver ions
combine with the chloride ions to form a precipitate of AgCl (s), which will be filtered
and washed. Since copper chloride and copper nitrate are both soluble, the copper
remains in solution. Any free nitric acid will be washed away when you rinse the
precipitate. so that only AgCl is remaining. As long as you dry the AgCl to constant
weight you should get the correct result.
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