Devise a test to distinguish between Cu2+ and Co2+.

test for how many valence electrons in outermost electron shell.

See your post above.

To devise a test to distinguish between Cu2+ and Co2+, we can use the approach of utilizing chemical reactions and selective reagents. Here's a step-by-step guide:

1. Obtain two separate test tubes and add a small amount of the unknown solution containing either Cu2+ or Co2+ ions to each tube.

2. To each test tube, add a few drops of 6M aqueous hydrochloric acid (HCl). This step is essential to ensure that the metal ions are converted into their chloride form. The reaction will be as follows:
Cu2+ or Co2+ + 4HCl → CuCl2 or CoCl2 + 2H2O

3. Now, we will use two distinct reagents for each tube to distinguish between Cu2+ and Co2+.

For the first test tube:
- Add a few drops of potassium iodide solution (KI) to one of the test tubes containing HCl and the unknown solution.
- If the color changes to brown or a brown precipitate forms, it indicates the presence of Cu2+ ions. This is because Cu2+ reacts with iodide ions (I-) to form CuI, which gives a brown color or precipitate.

For the second test tube:
- Add a few drops of sodium hydroxide solution (NaOH) to the other test tube containing HCl and the unknown solution.
- If a blue-green precipitate forms, it indicates the presence of Co2+ ions. This is because Co2+ reacts with hydroxide ions (OH-) to form Co(OH)2, which is a blue-green precipitate.

These reactions occur due to the unique properties of Cu2+ and Co2+ ions and the selective reagents that interact with them.

By performing these tests and observing the color changes or the formation of precipitates, you can differentiate between Cu2+ and Co2+ ions. Remember to interpret the results accurately by comparing them with known color references for Cu2+ and Co2+.