Equilibrium of a Sparingly Soluble Ionic Compound

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    Equilibrium Ionic
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Discussion Overview

The discussion revolves around the equilibrium of a sparingly soluble ionic compound, focusing on the concentration of hydroxide ions (OH-) and its implications for precipitation. Participants are engaged in a technical exploration of calculations related to solubility and concentration in a solution.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states an answer of 6.61g, but the context of this figure is unclear.
  • Another participant inquires if the goal is to find the highest concentration of OH- that avoids precipitation.
  • A request for clarification is made regarding which step in the calculations may be incorrect.
  • A participant notes the need to determine the mass in the actual solution based on the concentration calculated in g/L.
  • There is a question about the correctness of a previous statement or calculation.
  • One participant suggests that the discrepancy with the given answer may stem from rounding the concentration of OH- to 1.4e-6 M instead of using 1.435e-6 M, advocating for maintaining precision in calculations until the final rounding step.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views regarding the calculations and the implications of rounding in the context of the problem.

Contextual Notes

There are limitations regarding the assumptions made in the calculations, particularly concerning the definitions of concentration and the conditions under which precipitation occurs. The discussion does not resolve these mathematical steps or assumptions.

daphnelee-mh
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Homework Statement
I can't get the correct answer, isn't it if Ksp>[Mn2+][OH-]^2, there is no precipitation. How to get the specific concentration of [OH-]?
Relevant Equations
Kb = [NH4+][OH-]/[NH3]
Ksp=[Mn2+][OH-]^2
1572962999036.png

Answer given is 6.61g.
 
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You are looking for the highest concentration of OH- that doesn't produce precipitation, don't you?
 
chemistry.jpeg


May I know which step is wrong? thanks
 
You have worked out the concentration in g/L. What is the mass in the actual solution?
 
chemistry.jpeg


Is this correct ? thanks.
 
It is not quite equal to the given answer; I think that's because you rounded off [OH-] to 1.4e-6 M instead of 1.435e-6 M. Keep the extra digits through the calculation, and round off to the appropriate sig figs at the end.
 

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