Final Answer:
To separate the alloy of lanthanum oxide and chromium oxide, an effective method is to dissolve the alloy in hydrochloric acid. Subsequently, precipitate lanthanum oxalate by adding oxalic acid to the solution, while chromium remains in the solution.
Step-by-step explanation:
The choice of hydrochloric acid as the solvent addresses the issue encountered with sulfuric acid. While concentrated sulfuric acid might not effectively dissolve lanthanum oxide and chromium oxide alloy, hydrochloric acid provides an alternative that enhances the solubility of the components. The addition of oxalic acid then selectively forms lanthanum oxalate, which is sparingly soluble and precipitates out of the solution.
The chemical reactions involved in this process are:
Dissolving the alloy in hydrochloric acid:
La₂O₃ + Cr₂O₃ + 6HCl → 2LaCl₃ + 2CrCl₃ + 3H₂O
Adding oxalic acid to form lanthanum oxalate:
LaCl₃ + 3H₂C₂O₄ → La₂(C₂O₄)₃ + 6HCl
Lanthanum oxalate (La₂(C₂O₄)₃) precipitates, while chromium remains in the solution. This process enables the separation of lanthanum oxide and chromium oxide components in the alloy. The lanthanum oxalate precipitate can be filtered, washed, and further processed as needed. This method ensures a selective separation based on the different solubilities of lanthanum and chromium compounds under specific chemical conditions.