An unknown solution may contain one of the ions of the pair below. Devise a test which allows you to distinguish between the ions.
Cu2+(aq) and Co2+ (aq)
Add NH4SCN. Co(II) forms a tetrathiocyanate complex which is blue.
Cu(II) forma a black black ppt with KSCN
To devise a test that allows you to distinguish between Cu2+ (aq) and Co2+ (aq) ions in an unknown solution, you can use the concept of selective precipitation. Here's a step-by-step procedure:
1. Add a few drops of dilute sodium hydroxide (NaOH) solution to the unknown solution. Both Cu2+ and Co2+ will react with NaOH, but they form different precipitates.
2. Observe the color of the precipitate that forms. Copper (Cu2+) forms a blue precipitate called copper(II) hydroxide (Cu(OH)2), while cobalt (Co2+) forms a pink precipitate called cobalt(II) hydroxide (Co(OH)2).
- If a blue precipitate forms, it indicates the presence of Cu2+ ions in the unknown solution.
- If a pink precipitate forms, it indicates the presence of Co2+ ions in the unknown solution.
It's important to note that this test is specific to differentiating Cu2+ and Co2+ ions, but it may not work if other ions or compounds are present in the unknown solution. Therefore, it is recommended to carry out additional confirmatory tests if needed.