Question

A solution contains an unknown mixture of cations. During the third step of the scheme shown above, NaOH is added to the solution and a precipitate forms. Based on this observation, the solution likely contains which ions?

(A) Al3+, Cu2+, Fe2+
(B) Al3+, Cu2+, Fe3+
(C) Al3+, Fe2+, Fe3+
(D) Cu2+, Fe2+, Fe3+

Answer 1

The precipitate formed upon adding NaOH indicates the presence of Al3+, Cu2+, and iron ions (both Fe2+ and Fe3+), meaning Option B is likely correct.

Step-by-step explanation:

When NaOH is added to the solution and a precipitate forms, it suggests the presence of cations that react with OH- ions to form insoluble hydroxides. According to the provided information, trivalent metal ions like Al3+ precipitate as their hydroxides, such as Al(OH)3. Similarly, divalent iron Fe2+ as well as trivalent iron Fe3+ can form insoluble hydroxides, Fe(OH)2 and Fe(OH)3, respectively. Copper (Cu2+) also reacts with OH- to form insoluble Cu(OH)2. Hence, if a precipitate forms with the addition of NaOH, the solution likely contains Al3+, Cu2+, Fe2+, and Fe3+, which correspond to Option B: Al3+, Cu2+, Fe3+.