# Why do we use hydrochloric in the test for sulfate ions but nitric acid for halide ions?

Recently, I have learnt about testing for ions in qualitative analysis (BBC Bitesize).

The link above which I used for reference mentions that for the test for sulfate anions, hydrochloric acid $$(\ce{HCl})$$ is used to ensure that there is no presence of carbonate ions. For the test for halide ions $$(\ce{F-},$$ $$\ce{Cl-},$$ $$\ce{Br-},$$ $$\ce{I-},$$ etc), nitric acid $$(\ce{HNO3})$$ is used instead, for the same purpose.

I would like to know why the acids used are different, since they serve the same purpose.

Update: $$HCl$$ cannot be used for removal of carbonates in halides since $$HCl$$ contains the $$Cl-$$ halide. However, as to why nitric acid cannot be universally applied to all, I am still unsure.

• Wouldn't adding $\ce{HCl}$ interfere with a test for $\ce{Cl-}$? – MaxW Jul 17 at 15:33
• @MaxW how about adding nitric acid in the test for sulfate ions? – QuIcKmAtHs Jul 17 at 15:34
• Quoting the linked page: "Barium nitrate solution can be used instead of barium chloride solution. However, nitric acid is added first to acidify the test solution. Sulfuric acid cannot be used because it contains sulfate ions - these would interfere with the second part of the test." – Buck Thorn Jul 17 at 16:31