Optimizing Solubility: Manipulating [OH-] for Precipitation Control

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Discussion Overview

The discussion revolves around calculating the hydroxide ion concentration ([OH-]) required to lower the solubility of magnesium hydroxide (Mg(OH)2) to a specific value, using its solubility product constant (Ksp). The context is primarily homework-related, focusing on the application of Ksp in solubility calculations.

Discussion Character

  • Homework-related, Mathematical reasoning

Main Points Raised

  • One participant presents a homework statement asking for the [OH-] that would lower the solubility of Mg(OH)2 to 1.5 x 10^-5 mol/L, referencing the Ksp value of 1.5 x 10^-11.
  • Another participant suggests that an ICE table is unnecessary and recommends checking the [OH-] concentration that results in a [Mg2+] of 1.5 x 10^-5 M.
  • A participant attempts to formulate the relationship between the concentrations, questioning if 1.5 x 10^-5 = [Mg(OH)2]/[Mg][OH] is correct.
  • Two participants reiterate the formula for Ksp of Mg(OH)2, indicating it should be expressed as Ksp = [Mg(OH)2]/([Mg][OH]^2) and referencing the dissociation reaction.
  • One participant challenges another's understanding, suggesting they need to reread the book or consult other sources.

Areas of Agreement / Disagreement

There is no consensus on the correct approach to solving the problem, with differing opinions on the necessity of the ICE table and the formulation of the Ksp equation. Multiple competing views remain regarding the correct method to apply.

Contextual Notes

Participants express uncertainty about the correct application of Ksp and the use of the ICE table, indicating potential gaps in understanding or missing assumptions about the solubility equilibrium.

dav1d
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Homework Statement



What [OH-] would lower the solubility of Mg(OH)2
to 1.5 x 10-5 mol/L?
Ksp is 1.5 x 10-11 for Mg(OH)2.


Homework Equations



Ksp=products/reactants

The Attempt at a Solution



ICE box method

Mg OH (2) Mg(OH)2
initial: ? and I don't know what to do from here or even if this is the correct method to use.
 
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You don't need ICE table here, just check at what OH- concentration concentration of Mg2+ is 1.5x10-5M.
 
1.5 x 10^-5 = [Mg(OH)2]/[Mg][OH]

correct?
 
Write formula for Ksp of Mg(OH)2.
 
Borek said:
Write formula for Ksp of Mg(OH)2.

Ksp=products/reactants
=[Mg(OH)2]/[Mg][OH]^2

from the equation Mg+2OH = Mg(OH)2
 
No, you need to reread the book. Or check some other sources.
 

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