A confirmatory test in qualitative analysis is a chemical test performed to definitively verify the presence of a specific ion or compound in a sample. It is usually done after an initial or preliminary test suggests that the substance may be present.
Here’s what makes it important:
- Purpose:
- To confirm the identity of an ion or compound.
- Eliminates false positives that may occur in preliminary tests.
- How It Works:
- The sample is treated with a specific reagent that reacts only with the ion or compound of interest.
- The reaction produces a distinct color, precipitate, or gas that is characteristic of that substance.
- Examples:
- Chloride ions (Cl⁻):
- Preliminary test: Formation of a white precipitate with AgNO₃.
- Confirmatory test: The precipitate dissolves in ammonium hydroxide, confirming Cl⁻.
- Sulfate ions (SO₄²⁻):
- Preliminary test: Reaction with BaCl₂ gives a white precipitate.
- Confirmatory test: The precipitate is insoluble in HCl, confirming sulfate.
- Copper ions (Cu²⁺):
- Preliminary test: Blue precipitate with NaOH.
- Confirmatory test: Formation of a deep blue tetraammine copper complex with NH₃.
- Chloride ions (Cl⁻):
- Importance:
- Ensures accuracy in identifying ions or compounds.
- Reduces the risk of misinterpretation due to interfering ions or similar reactions.
In short:
A confirmatory test is a definitive test in qualitative analysis that confirms the presence of a specific substance using a reaction that is unique to that substance.