If you wash with nitric acid, a high electrolyte concentration is maintained and the AgCl particles stay clotted together. When you dry the precipitate, the acid decomposes and volatilizes, so it shouldn't have a strong effect on the precipitate mass. But the clotted precipitate will always be contaminated with silver nitrate. Silver nitrate has a molecular weight of 169.87, and silver chloride only 143.32, so the mass of the precipitate will be a little high.
Author: Fred Senese email@example.com
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/moles/faq/print-agcl-ppt-wash.shtml