Test for chlorides and sulfates

[dioprem]

Hi guys needed to check up on something. Recently in school we were taught that in order to test for the presence of chloride ions, we had to add acidified silver nitrate to check for the precipitation of silver chloride. Similarly, to test for sulfates, we were told to add acidified barium nitrate to check for the precipitation of barium sulphate.

I am confused by the "acidified" portion. Say I am testing for chlorides. I am supposed to add nitric acid as well as silver nitrate. When I asked why this was so, I was told that it was to eliminate any other potential silver salt from precipitating. So any precipitate I saw would only be silver chloride and not some other silver salt. Thus I would know for sure that chloride ions were present.

How does adding nitric acid eliminate other possibilities?

 

[Borek]

Think what other salts are possible, think about strength of the other acids.

--