One can distinguish sodium chloride from sodium iodide by looking at the precipitate formed after adding the salts to separate silver nitrate solutions. Sodium chloride reacts with silver nitrate to form a white silver chloride precipitate, while sodium iodide reacts with silver nitrate to form a yellow silver iodide precipitate.
Another way to distinguish sodium chloride from sodium iodide is by adding the salts to concentrated sulfuric acid. Sodium chloride forms a colorless hydrogen chloride gas, while sodium iodide forms hydrogen sulfide gas and a brown triiodide solid. The results of the above reactions may be further confirmed by testing the salts with a starch solution. Sodium iodide reacts with starch to form a dark blue-black precipitate, while sodium chloride does not form this dark precipitate.