Question

Why is it necessary to wash silver chloride before drying it?

Answer 1

Because that is the standard work-up for precipitates.........

Explanation:

You got a slurry of insoluble `AgCl` as a white solid. The curdy precipitate can occlude some other halide salts UNLESS you give it a good wash with water. And of course here you face the problem that the silver chloride is photoactive, and could photo-reduce to silver metal. And this used to be basis of old black and white photography.