In CuSO4 solution, why doesn't Cu(OH)2 precipitate out?

  • Thread starter wywong
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In summary, the conversation discusses the solubility and precipitation of Cu(OH)2 in aqueous solutions of CuSO4. It is suggested that the presence of complex ions, such as CuOH+, Cu2(OH)22+, and Cu(OH)42-, may prevent Cu(OH)2 from precipitating out. The stability constant and solubility product of these complexes may play a role in determining their formation and the solubility of Cu(OH)2. However, the exact details and sources of this information are not readily available.
  • #1
wywong
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An aqueous solution of CuSO4 has a pH around 4. That means there are more H+ ions than OH-. Since the H+ ions come from dissociation of water, there must be an equal amount of OH-. Where have all the OH- ions gone? I suppose they are locked up as Cu(OH)2. However, the latter is highly insoluble in water. So why doesn't Cu(OH)2 precipitate out? I guess chelation of Cu(OH)2 by H3O+ may make it soluble. However, I have been unable to find any information about such chelation. Can anyone help?

CuCl2, AlSO4, CaCl2 etc. all pose a similar problem.

Many TIAs.

Wai Wong
 
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  • #2
Solution may contain some amount of copper (or other cation) complexed by OH- groups. There usually whole families of soluble complexes - like CuOH+, Cu2(OH)22+, Cu(OH)42- - involved.

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  • #3
Thanks Borek!

BTW, I think Cu(OH)42- shouldn't be there, or otherwise Cu(OH)2 would be soluble in water or alkaline solutions.

Wai Wong
 
  • #4
It depends on the relative values of the stability constant and solubility product. These are taken from the equilibria database, that means it is possible to trace the source of the information.

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  • #5
I am not good at finding those constants, but according to several sources, Cu(OH)42- forms only at very high pH, suggesting a low stability constant.

Never mind. The root of my question has already been well answered.

Thanks

Wai Wong
 

FAQ: In CuSO4 solution, why doesn't Cu(OH)2 precipitate out?

Why does Cu(OH)2 not precipitate out in CuSO4 solution?

When CuSO4 is dissolved in water, it dissociates into Cu2+ and SO4 2- ions. These ions are highly soluble in water and do not have a tendency to combine and form a precipitate. Therefore, the Cu2+ ions remain in solution and do not form Cu(OH)2.

What is the solubility of Cu(OH)2 in CuSO4 solution?

The solubility of Cu(OH)2 in CuSO4 solution is very low, as the presence of SO4 2- ions prevents the formation of Cu(OH)2. The solubility can be further decreased by adding a strong acid, which would react with the OH- ions and shift the equilibrium towards the formation of water molecules instead of Cu(OH)2.

Can Cu(OH)2 precipitate out in the presence of other ions?

In the presence of other ions, the formation of Cu(OH)2 may be hindered due to the formation of complex ions. For example, if ammonia (NH3) is present, it can react with Cu2+ to form a complex ion, [Cu(NH3)4]2+, which is more stable than Cu(OH)2 and therefore prevents its formation.

Is there any way to make Cu(OH)2 precipitate out in CuSO4 solution?

Yes, there are ways to make Cu(OH)2 precipitate out in CuSO4 solution. One way is to decrease the solubility of CuSO4 by adding a salt such as NaCl, which would shift the equilibrium towards the formation of Cu(OH)2. Another way is to increase the pH of the solution, which would favor the formation of Cu(OH)2 over the Cu2+ ions.

What is the chemical reaction that takes place when Cu(OH)2 precipitates out in CuSO4 solution?

The chemical reaction that takes place when Cu(OH)2 precipitates out in CuSO4 solution is: CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4. This reaction occurs when a base, such as sodium hydroxide (NaOH), is added to the solution, resulting in the precipitation of Cu(OH)2. The sodium ions (Na+) combine with the sulfate ions (SO4 2-) to form sodium sulfate (Na2SO4), which remains in solution.

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