Question 22
NECO
•
2019
•
CHEMISTRY
•
objective
A sample solution contains two metal ions selected from Fe^{3+}, Cu^{2+}, Ni^{2+} and Zn^{2+}. The following sequence of tests is performed:\n1. To 5.0 mL of the solution, a few drops of dilute NaOH are added, producing a precipitate.\n2. Excess NH_{4}OH is then added, and the precipitate dissolves, giving a clear deep‑blue solution.\n3. Finally, dimethylglyoxime (DMG) solution is added, resulting in a bright red precipitate.\nIdentify the metal ion(s) present in the original sample and write the net ionic equation for the formation of the red DMG precipitate.
Answer Options
A.
Cu^{2+} and Ni^{2+} are present; \(\text{Cu}^{2+} + 2\,\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2} + 2\,\text{OH}^{-} \rightarrow \text{Cu}(\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2})_{2}\,\downarrow + 2\,\text{H}_{2}\text{O}\)
B.
Fe^{3+} and Zn^{2+} are present; \(\text{Zn}^{2+} + 2\,\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2} + 2\,\text{OH}^{-} \rightarrow \text{Zn}(\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2})_{2}\,\downarrow + 2\,\text{H}_{2}\text{O}\)
C.
Cu^{2+} and Fe^{3+} are present; \(\text{Fe}^{3+} + 2\,\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2} + 2\,\text{OH}^{-} \rightarrow \text{Fe}(\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2})_{2}\,\downarrow + 2\,\text{H}_{2}\text{O}\)
Correct Answer
D.
Cu^{2+} and Ni^{2+} are present; \(\text{Ni}^{2+} + 2\,\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2} + 2\,\text{OH}^{-} \rightarrow \text{Ni}(\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2})_{2}\,\downarrow + 2\,\text{H}_{2}\text{O}\)
Correct Answer
D
Correct Option:
Cu^{2+} and Ni^{2+} are present; \(\text{Ni}^{2+} + 2\,\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2} + 2\,\text{OH}^{-} \rightarrow \text{Ni}(\text{C}_{4}\text{H}_{5}\text{N}_{2}\text{O}_{2})_{2}\,\downarrow + 2\,\text{H}_{2}\text{O}\)
About This Question
This is
Neco
2019
Chemistry
Question 22.
It is one of the
objective
questions from the
2019
Neco
Chemistry
examination.
Difficulty level:
Hard
.