When iodide ions (I-) are mixed with silver nitrate (AgNO3), a chemical reaction takes place, resulting in the formation of a new compound called silver iodide (AgI) and sodium nitrate (NaNO3). The reaction can be represented by the following equation:

AgNO3 (aq) + KI (aq) → AgI (s) + NaNO3 (aq)

In this reaction, silver ions (Ag+) from silver nitrate combine with iodide ions (I-) from potassium iodide to form a solid precipitate of silver iodide. Silver iodide is a pale yellow, insoluble compound, while sodium nitrate remains dissolved in the solution. The precipitation of silver iodide can be observed as a cloudy or milky appearance in the mixture.

The reaction between silver nitrate and potassium iodide is a classic example of a precipitation reaction, where two soluble salts react to form an insoluble product. This type of reaction is commonly used in qualitative analysis to identify and separate different ions in a solution.