Which chemical test would be used to identify sulfate ions in a solution?

To identify sulfate ions in a solution, the test involves adding barium chloride. This method relies on the formation of a white precipitate when barium chloride is introduced to a solution containing sulfate ions. The chemical reaction that occurs is as follows:

[ \text{Ba}^{2+} (aq) + \text{SO}_4^{2-} (aq) \rightarrow \text{BaSO}_4 (s) ]

The resulting barium sulfate precipitate is insoluble in water, and its formation is a strong indication of the presence of sulfate ions in the solution. This test is specifically useful because it provides a clear visual cue (the white precipitate) that can easily be observed.

In contrast, adding sodium hydroxide would not directly identify sulfate ions; it is used for the identification of certain metal cations. Potassium iodide is generally used to test for the presence of lead(II) ions or other specific ions, not sulfate. Silver nitrate is primarily utilized to test for halide ions rather than sulfate ions, and it would react differently. Thus, barium chloride is the appropriate reagent for confirming the presence of sulfate ions due to the distinct precipitate that forms.