Equilibrium of Cobalt complexes
- Page ID
- 128809
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Required Training |
Required PPE |
|---|---|
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
|
Large test tube |
~10 mL 0.2 M CoCl2 · 6H2O (MW: ~238) |
|
DI water squirt bottle |
Concentrated HCl in a drip top bottle |
|
Hot water bath |
|
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Ice/salt bath |
|
Procedure:
- Putting drops of conc. HCl will change the pink solution to blue
- Adding water changes the solution back to pink
- This reaction can have several color changes if given a large enough test tube.
- Heat will turn the solution blue, and the ice/salt bath will turn it pink.
- It is possible to turn only half of the test tube a color by carefully immersing it in a hot/ice bath with a steady hand.
Discussion:
This demonstration operates on the following reaction:
Co(H2O)62+aq + 4 Cl-aq (+ heat) → CoCl42-aq + 3 H2Ol
The blue form is anhydrous and tetrahedral coordinated, the pink form is hydrated and is octahedral coordinated. ΔH = ~42-54kJ/mol. Conc. HCl is not only a source of Cl- but also has a dehydrating effect. This demonstration projects well on an overhead, with a petri dish.
Hazards:
Be careful when using conc. HCl and make sure to wear all PPE. If you get any solution on your skin, be sure to wash for 15 minutes.
SOP:
Corrosive – Hydrochloric Acid
Disposal (by Storeroom)
Return the demonstration to the storeroom, where the cobalt waste will be submitted to EH&S.