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Saturation of a salt

1. What is the saturated [Al3+] concentration at pH7 made by the addition of AlCl3 to distilled water?



2. AlCl3<-->Al3++3Cl-
3H2O<-->3H++3OH- Kw=1x10-14
Al3++3OH-<-->Al(OH)3 Ksp=3x10-34




3. I'm familiar with this type of problem, but not the way in which it's being asked. I hope I have included the equations and constants that are pertinent below. I would start by taking the Ksp for the precipitate and mulitplying it by 1/Kw. This multiplied by the solubility product for AlCl3 should give the equilibrium product for the whole equation, but I don't know how to get that.
 

Borek

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Unfortunately question is ambiguous. It is not entirely clear to me it if should be read as "you add AlCl3 to distilled water at pH 7.0, what is the resulting [Al3+]" or "you added AlCl3 to distilled water and you fund pH to be 7.0, what is [Al3+]". These are different problems.

I guess it has to be read the second way. If so... what is concentration of OH-?
 
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