Devise a test to distinguish between Cu2+ and Co2+.
To distinguish between Cu2+ (copper) and Co2+ (cobalt) ions, we can perform a series of chemical tests. Here's a step-by-step procedure:
1. Test 1: Reaction with Sodium Hydroxide (NaOH)
- Take a small amount of the unknown solution (containing either Cu2+ or Co2+ ions) in a test tube.
- Add a few drops of NaOH solution to the test tube.
- Observe the color change:
- If a blue precipitate forms, it indicates the presence of Cu2+ ions. Copper hydroxide (Cu(OH)2) is pale blue and insoluble in water.
- If a pink precipitate forms, it indicates the presence of Co2+ ions. Cobalt hydroxide (Co(OH)2) is pink and relatively insoluble.
2. Test 2: Reaction with Ammonia (NH3)
- Take another small amount of the unknown solution in a different test tube.
- Add a few drops of ammonia solution (NH3) to the test tube.
- Observe the color change:
- If the solution turns deep blue, it confirms the presence of Cu2+ ions. Cu(NH3)4^2+ complex forms, which has a deep blue color.
- If the solution remains pink or changes to a different color, it suggests the presence of Co2+ ions. Cobalt does not readily form a stable complex with ammonia.
3. Test 3: Formation of Complexes
- For confirmation, you can perform further tests to form more stable complexes with ligands specific to Cu2+ and Co2+.
- For Cu2+:
- Add a few drops of potassium ferrocyanide (K4[Fe(CN)6]) solution to a sample of the unknown solution. A brown precipitate (copper(II) ferrocyanide) indicates the presence of Cu2+ ions.
- For Co2+:
- Add a few drops of dimethylglyoxime solution to another sample of the unknown solution. A crimson red color or precipitate (cobalt(II) dimethylglyoxime complex) confirms the presence of Co2+ ions.
By systematically conducting these tests, you can distinguish between Cu2+ and Co2+ ions based on the observed color changes and precipitate formations.