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.

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[quicknote]

Adding nitric acid helps to create a more acidic environment, which prevents the formation of other silver salts that may also precipitate in the presence of silver nitrate. This is important because different silver salts have different solubility in water, so by creating an acidic environment, we can ensure that only silver chloride will precipitate. This allows for a more accurate test for the presence of chloride ions. Similarly, adding acidified barium nitrate for the sulfate test helps to prevent the formation of other barium salts, ensuring that only barium sulfate will precipitate. Overall, the acidification step helps to increase the specificity and accuracy of the test for chlorides and sulfates.