Question

Aqueous ammonia is used as a precipitating reagent for Al3+ ions as Al(OH)3 rather than aqueous NaOH, because :

• A. N is a weak base
• B. NaOH is a very strong base
• C. NaOH forms [Al(OH)4]- ions
• D. NaOH forms [Al(OH)2]+ ions

Answer 1

Answer: (C)

NaOH forms $Al(OH)4$- ions

Answer 2

Al(OH)3 (amphoteric hydroxide) + OH– $\longrightarrow$ [Al(OH)4]– (soluble complex)