Why is dilute nitric acid added before silver nitrate during ion testing?

Adding dilute nitric acid before introducing silver nitrate is crucial for effective ion testing because it serves to remove any carbonate ions that might be present in the solution. When carbonate ions are present, they can react with silver nitrate to form a precipitate of silver carbonate, which would interfere with the identification of silver ions.

By adding dilute nitric acid, any carbonate ions react with the acid to form carbon dioxide and water, effectively eliminating them from the solution. This ensures that when silver nitrate is subsequently added, it can react solely with silver ions without the interference of other precipitation reactions.

Thus, this step is essential for obtaining accurate results during ion testing, as it allows for a clearer and more reliable identification of the specific ions present.