[Aerlinn]

We did an experiment with the equliibrium: Co2+(aq) + 4Cl-(aq) <---> CoCl4(2-) (aq)
Co2+(aq) is pink (I'm guessing it's hydrated crystals in solution, 'cause anhydrous CoCl2 is blue?), Cl-(aq) is colourless, CoCl4(2-)(aq) is blue.
Basically, we did 3 tests.

Test A: Temperature change. Test tube, with 5ml CoCl2 mixed with 4ml NaCl, a watermelon pink solution
Results: Placed in HOT water: Dark pink
In COLD water: Light red

I deduced that the equilibrium above was endothermic... is it?
Do the Co2+ ions come from CoCl2 and the Cl- ions come from both CoCl2 and NaCl, and the Na+ just float in solution? (So would the NaCl affect the [Cl-] too?)

Test B: Change in Chloride ion concentration.
5ml CoCl2: red pink
Add 5ml concentrated HCl: purple
Add 5ml AgNO3: white pink (milky pink)

I have trouble deciphering what happens in this one. Is the milky pink because AgCl precipitate forms in the third one? Would we call this: Ag+(aq) + Cl-(aq) <---> AgCl(s) the completing equilibria?


Test C: Effects of dilution
5ml 1-propanol (clear), add 1 ricegrain amount of CoCl2: blue colour
Water added drop by drop till colour change: White precipitate forms at bottom, pink froth at the top.

What's happening in this last test? i.e.. Why CoCl2 was added to 1-propanol before diluting (there has to be a reason =S-- just to dissolve the CoCl2? Is it possible to dissolve something without water? Because aren't ions aqueous.. ), why only a ricegrain amount of CoCl2 was added, what the blue colour is (Random guess: CoCl2 undergoing the above equilibrium, and something causes it to have a net forward reaction? (if so, what causes it to favour the forward reaction?)), what the identity of the precipitate is, what the pink froth is... =S
~~~

Update: My teacher was all 'normally you should avoid using ions which are present in the equilibrium expression. Huh? If that should be avoided, wonder why NaCl (with Cl-) was added to CoCl2(aq), couldn't we have just had CoCl2(aq) and that would have formed ions Co2+(aq) and Cl-(aq) and established the equilibrium?

Someone came up with the fact that the precipitate might be C3H7C1 Think water might react to form it too? Maybe someone can tell me how you can come up with the precipitate?

Just having trouble interpreting the results of the experiment, so hoping someone can help me with it today...