Question

When we dissolve CuCl2 in water it turn a blue color, http://puu.sh/64Lzr.jpg meaning we have more Cu2+ than CuCl2 (aq), but when we add A LOT of CuCl2 to that mixture then it becomes green! How does that happen? How does the equilibrium shift to the left when we add CuCl2? we dont add Cu2+ or Cl- or anything!

Answer 1

do you what species produces the green colour?

Answer 2

Cu2+ is blue , CuCl2(aq) is green, when we dissolve CuCl2(s) in water we get a blue solution, meaning all dissolved molecules ionized in solution (strong electrolyte). If you keep adding solid copper sulfide, it will convert to Cu2+ and Cl- , but overtime the concentration of both the little CuCL2 (aq) in solution and the Cu2+ (aq) WILL INCREASE. Isnt that the same as a volume decrease? And a volume decrease causes the same results because it increase concentrations of both reactants and products , this is what happens overtime when we add solid CuCl2!!!! So my conclusion is that it will shift the equilibrium just as a volume decrease (concentration increase of both react & prod) would do, meaning to the side with lowest coeffiients and THAT IS (!!) CuCl2(as), meaning the solution will turn GREEN! :D Do you agree with me aaronq? I just came to that realization I dont know if its correct though!

Answer 3

Someone told me that this http://puu.sh/64Lzr.jpg equilibrium is entirely wrong and THAT CuCl2 (aq) does NOT cause the green color!! Now Im completely brain fluttered (excuse me for my language).
He told me that [Cu(H2O)6]2+ + 4 Cl- <-> [CuCl4]2- + 6 H2O is the correct equilibrium.
[CuCl4]2- : green
[Cu(H2O)6]2+: blue

Then he told me that [CuCl4]2- is formed by Cu2+ + 4 Cl- -> [CuCl4]2- : green
and [Cu(H2O)6]2+ is formed by Cu2+ + 6 H2O -> [Cu(H2O)6]2+ : blue
Now if that is the case, the Original equilibrium in my book is NOT CORRECT, because
there is no indication that CuCl2(aq) indeed is responsible for the green color.

Answer 4

yeah, i imagined it had to do with coordination around the \(Cu^{2+}\) ion. I'm pretty sure the second equilibrium is correct.

Answer 5

but why is my book telling me that CuCl2(aq) is responsible for the green color?: http://puu.sh/64Lzr.jpg
They say that if we increase the volume the equilibrium shifts to the side with the highest sum of coeff. so it will turn from green to blue.

Answer 6

but you're not increasing the volume.

Wiki says that in it's anhydrate form, it's brownish.
http://en.wikipedia.org/wiki/Copper(II)_chloride

Answer 7

I am increasing the volume, as you can see in the picture water has been added to the solution, then it turned blue.

Answer 8

but you said you added much more CuCl2

Answer 9

flutter sorry I just posted this message on accident

Answer 10

regarding when I said that if we keep adding the solid, thats another problem. But now someone told me that the equilibrium from my book is incorrect. and that the CuCl2 is not the substance that is responsible for the green color, while my book says yes as in the link.

Answer 11

that's weird. I think your book is also incorrect. I agree with whoever said that the \(CuCl^{2+}_4\) causes the green colour.

Answer 12

On that page i posted earlier, it says that \([Cu(H_2O)Cl_2]\) is blue.

Answer 13

http://gyazo.com/b16f1381d53561858ce7ca4cc32adeca So this is incorrect, that is exactly what is in my book :p

Answer 14

can you tell me if CuCl2 (aq) molecules exist?

Answer 15

as shown in the link they are molecules, but I am unsure of that, because I cannot believe that these molecules exist.

Answer 16

we'll it's not \(Cu^{2+}\) that is blue, its \(Cu(H_2O)_6^{2+}\) that makes it appear that colour.

Answer 17

technically, CuCl2, is not a "molecule" because they are joined by ionic bonds.

Answer 18

I think this entire equilibrium from my book: http://gyazo.com/b16f1381d53561858ce7ca4cc32adeca is just complete garbage, because there is not equilibrium between CuCl2 (aq) and the ions, because CuCl2(aq) doesnt exist ? and it does not cause the green color as you and someone else mentioned.

Answer 19

it would exist as an anhydrous solid, but when dissolved in water:
\(CuCl_{2~(s)} +2~H_2O_{(l)} \rightleftharpoons [Cu(H_2O)_2Cl_2]_{(aq)} \)

Answer 20

lol clearly I do not know anything about chemistry or I am completely retarded. No I think its the book :D Thank you for the help I think the book is trying to explain basic stuff so they invent some nonsense to explain it.

Answer 21

clearly CuCl2 is not the cause of the green color, the book is garbage. do you agree?

Answer 22

lol nah, don't say that. Inorganic chemistry gets very strange. I think your book is trying to omit some information to make things easier because they're not easy concepts (have you learned about crystal field theory?). A lot of the concepts you'll learn in high school (or it's equivalent in your country) will be watered-down material.

Yeah, CuCl2 is definitely not green. :S

Answer 23

and CuCl2 (aq) does note exist either, making the equilibrium total nonsense. Thank you for informing me about these mistakes :)

Answer 24

yeah, i mean, your teacher might expect you to go with that if it's in your book, but yes, it's technically wrong.. no problem, dude!

Answer 25

[CuCl4]2- : green
[Cu(H2O)6]2+: blue

I think this is the right answer.
Cu2+ ions are complexed, either by water or by chloride ions.

I do not think such a thing as CuCl2(aq) exists at all.