Q1: What is the group reagent used to precipitate Group IIIA cations (Al3+, Cr3+, Fe3+)?
Explanation: The group reagent for Group IIIA cations is NH₄Cl + NH₄OH, which precipitates Al(OH)₃, Cr(OH)₃, and Fe(OH)₃.
Q2: What is the color of the precipitate formed by Al3+ in the presence of NH₄Cl + NH₄OH?
Explanation: Al3+ forms a gelatinous white precipitate of Al(OH)₃ in the presence of NH₄Cl + NH₄OH.
Q3: What is the color of the precipitate formed by Cr3+ in the presence of NH₄Cl + NH₄OH?
Explanation: Cr3+ forms a green precipitate of Cr(OH)₃ in the presence of NH₄Cl + NH₄OH.
Q4: What is the color of the precipitate formed by Fe3+ in the presence of NH₄Cl + NH₄OH?
Explanation: Fe3+ forms a reddish brown precipitate of Fe(OH)₃ in the presence of NH₄Cl + NH₄OH.
Q5: Which of the following precipitates dissolves when boiled with NaOH?
Explanation: Al(OH)₃ dissolves when boiled with NaOH, forming Na₂Al₂O₄ or Na[Al(OH)₄], due to its amphoteric nature.
Q6: How is Cr(OH)₃ dissolved after being precipitated?
Explanation: Cr(OH)₃ is dissolved by heating with NaOH and H₂O₂, which oxidizes Cr3+ to CrO₄²⁻ (chromate).
Q7: What is the confirmatory test for Cr3+, and what color is observed?
Explanation: Cr3+ is confirmed by forming a yellow precipitate of PbCrO₄, which is soluble in NaOH, indicating the presence of chromate ions.
Q8: What happens to Fe(OH)₃ when heated with NaOH and H₂O₂?
Explanation: Fe(OH)₃ is insoluble in NaOH and H₂O₂, remaining as a reddish brown precipitate.
Q9: What is the confirmatory test for Fe3+, and what color is observed?
Explanation: Fe3+ is confirmed by dissolving Fe(OH)₃ in dilute HCl and adding KSCN or NH₄SCN, which forms a characteristic red precipitate or color.
Q10: What is the confirmatory test for Al3+, and what color is observed?
Explanation: Al3+ is confirmed by reacting with aluminon in NH₄OH, forming an eye-catching red precipitate.
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