Question

Below is an analysis scheme for a mixture of Co2+, Cu²+, Fe3+, and Ni2+. You are asked for the formula of each cited precipitate and for the formula of the cation in the final solution. Include the net ionic chemical equations for the precipitation reactions. Step 1. In test tube 11, potassium nitrite acidified with acetic acid is added to the mixture of the four cations (the anion present is nitrate). A precipitate is produced. The aqueous solution is decanted off of the precipitate into test tube 12. What is the formula for the precipitate in test tube 112 Step 2. Aqueous ammonia is added to the solution in test tube 12 until the solution is basic. A precipitate is produced. The aqueous solution is decanted off of the precipitate into test tube 3. What is the formula for the precipitate in test tube 12? Step 3. An ethanol solution of dimethylglyoxime is added to the solution in test tube 13. A precipitate is produced. The aqueous solution is decanted off of the precipitate into test tube 14. What is the formula for the precipitate in test tube 13? What is the formula for the transition metal cation in test tube ? Step 4. To check that indeed there is a final transition metal cation in the solution in test tube 14, another sample of the original mixture of all four cations is tested with aqueous potassium iodide. A precipitate forms. What is the formula for this confirming precipitate?

Answer 1

The formula for the confirming precipitate is CoI₂.

Therefore, the final formula for each precipitate is:

Cu(NO₂)₂ in test tube 11

Fe(OH)₃ in test tube 12

Ni(C₄H₆N₂O₂)₂ in test tube 13

CoI₂ in the confirming precipitate

The formula for the transition metal cation in the test tube 14 is Co²+.

Step-by-step explanation:

Step - 1: By adding potassium nitrite that has been acidified with acetic acid, Cu2+ cations will be precipitated as Cu(NO2).₂. The precipitate in test tube 11 has the formula Cu(NO2)2.

Cu²+(aq) + 2NO₂⁻(aq) + 2H⁺(aq) → Cu(NO₂)₂(s) + 2H₂O(l)

Step - 2: By adding aqueous ammonia to the solution in test tube 12, Fe3+ cations will precipitate as Fe.(OH)3. The precipitate in test tube 12 has the formula Fe(OH)3.

Fe³+(aq) + 3OH⁻(aq) → Fe(OH)₃(s)

Step - 3: By adding an ethanol solution of dimethylglyoxime, the Ni2+ cations will precipitate specifically as Ni(C4H6N2O2).₂. The formula for the precipitate in test tube 13 is Ni(C₄H₆N₂O₂)2. Co2+ is the transition metal cation present in test tube 14.

Ni²+(aq) + 2C₄H₆N₂O₂⁻(aq) → Ni(C₄H₆N₂O₂)₂(s)

Step - 4. The addition of aqueous potassium iodide to the original mixture of all four cations will precipitate Co²+ cations as CoI₂. The confirming precipitate has the formula CoI2.

Co²+(aq) + 2I⁻(aq) → CoI₂(s)