Using Acidified silver nitrate solution to test for the presence of halides

Acidified silver nitrate can test for halides to give precipitate. Remember it do give positive result for halides, not only chloride ions.

(pale) Yellow precipitate forms when iodide (bromide) ions is used, white precipitate forms when there are chloride ions.

Here are the reasons why silver nitrate has to be acidified for testing purpose from Wikipedia:
Silver nitrate are typically acidifed with dilute nitric acid to remove interfering ions, e.g. carbonate ions and sulfide ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides. Addition of AgNO3 to the resulting solutions produces a precipitate in the presence of halides. The color of precipitate varies with the halide.