Why is my silver chloride precipitate gray and clumpy instead of white?

[Joshua66]

I’m trying to precipitate silver chloride from a solution of silver nitrate and sodium chloride, but my product keeps coming out looking more gray and clumpy instead of the fine white powder I expected. I’m wondering if the concentration of my reactants or the stirring rate during the double displacement reaction is causing this.

[Gary.W]

AgCl should be a fine white precipitate. Gray and clumpy often means impurities or light exposure. AgCl is photosensitive and can darken to gray or black when exposed to light; storage in light can cause this. Impurities from glassware or the stirrer can also seed aggregates.

[GregoryJ]

I once saw chunky gray stuff when the mix was pretty concentrated and I stirred hard. The particles stuck together and settled as a rough lump. When I slowed the stirring a bit and let things nucleate, the texture improved sometimes, but it never looked perfect.

[JeffreyLH]

Concentration does affect the precipitation rate. If the solution is very supersaturated you get lots of nucleation and fast growth, which can push particles to join up into bigger clumps rather than a fine powder. In practice, keeping things moderately dilute and letting nucleation happen slowly can help, but results can be inconsistent.

[Mia52]

Could the problem be mainly light exposure rather than stirring? If the precipitate darkens when left in light, that points to photo reduction of AgCl to metallic silver. Storing and handling in the dark might change what you see.