Ammonium acetate plays a crucial role in the gravimetric determination of aluminum as oxinate (aluminum oxinate, Al(C₉H₆NO)₃). Here's why:

1. Buffering Agent:

* Ammonium acetate acts as a buffer solution, maintaining a specific pH range (around 4-5) during the precipitation process. This is essential for the complete and quantitative precipitation of aluminum as aluminum oxinate.

* At this pH, the aluminum ions (Al³⁺) react with the 8-hydroxyquinoline (oxine) reagent to form the insoluble aluminum oxinate precipitate.

* If the pH is too high, aluminum hydroxide (Al(OH)₃) may precipitate, leading to incomplete precipitation of aluminum oxinate.

* If the pH is too low, the solubility of aluminum oxinate increases, resulting in a lower yield.

2. Providing a Suitable Environment for Precipitation:

* The ammonium acetate buffer solution helps create a suitable ionic environment for the formation of the aluminum oxinate precipitate.

* The acetate ions (CH₃COO^-) from ammonium acetate can interact with the aluminum ions, preventing the formation of other undesired precipitates.

3. Minimizing Interferences:

* In the presence of other metal ions, ammonium acetate can help minimize interferences by adjusting the pH and providing a favorable environment for selective precipitation.

In summary, ammonium acetate in gravimetric determination of aluminum as oxinate:

* Buffers the solution to maintain the optimal pH for complete precipitation.

* Creates a favorable environment for the formation of the aluminum oxinate precipitate.

* Minimizes interferences from other metal ions.

By fulfilling these roles, ammonium acetate ensures the accurate and reliable determination of aluminum in the sample through the gravimetric method.