Al3+ Concentration at pH 7 from AlCl3 Addition to Distilled Water

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SUMMARY

The discussion centers on determining the saturated concentration of Al3+ ions at pH 7 resulting from the addition of AlCl3 to distilled water. The relevant chemical equilibria include the dissociation of AlCl3 into Al3+ and Cl- ions, as well as the formation of Al(OH)3 precipitate governed by its solubility product (Ksp = 3x10^-34) and the water dissociation constant (Kw = 1x10^-14). The ambiguity in the question regarding whether to consider the addition of AlCl3 or the resulting pH of 7 is noted, impacting the calculation of OH- concentration and Al3+ equilibrium. The discussion emphasizes the need for clarity in interpreting the problem to derive accurate results.

PREREQUISITES
  • Understanding of chemical equilibria and solubility products (Ksp)
  • Familiarity with acid-base chemistry, particularly pH and hydroxide ion concentration
  • Knowledge of the dissociation of salts in aqueous solutions, specifically AlCl3
  • Basic proficiency in algebraic manipulation of equilibrium expressions
NEXT STEPS
  • Research the calculation of ion concentrations from solubility products, focusing on AlCl3
  • Study the relationship between pH and hydroxide ion concentration in aqueous solutions
  • Explore the concept of complex ion formation and its impact on solubility
  • Investigate the effects of varying pH on the solubility of metal hydroxides, particularly Al(OH)3
USEFUL FOR

Chemistry students, environmental scientists, and professionals involved in water treatment processes or metal ion chemistry will benefit from this discussion.

deserthaze06
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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.
 
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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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