Solubility in g/L of zinc hydroxide with pH of 8

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Discussion Overview

The discussion revolves around the solubility of zinc hydroxide (Zn(OH)2) in a solution with a pH of 8. Participants explore the implications of pH on solubility, the role of hydroxide ions, and the necessity of knowing the solubility product constant (Ksp) for accurate calculations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant attempts to calculate the solubility based on the pOH derived from the pH but expresses uncertainty about the correctness of their approach.
  • Another participant questions the calculations and asks for clarification on the number of hydroxide ions per molecule of zinc hydroxide.
  • It is noted that the hydroxide ions present in the solution may not originate from the dissolved zinc hydroxide, suggesting a need to consider the Ksp in calculations.
  • Some participants highlight the ambiguity in the question regarding whether the pH of 8 is maintained through buffering or if it is an initial condition without buffering.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the pH condition and its implications for solubility calculations. There is no consensus on how to approach the problem due to the ambiguity present in the question.

Contextual Notes

Participants note the importance of the Ksp value for zinc hydroxide in determining solubility and the potential impact of buffering on the pH level, which remains unresolved.

Scatteredheroes
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Homework Statement



Zinc hydroxide has the chemical formula of Zn(OH)2. It has a very low solubility. What is the solubility in g/L of Zinc Hydroxide in a solution with a pH of 8?

Homework Equations



zinc hydroxide formula
14-pH = pOH[/B]

The Attempt at a Solution



10^-6 (the pOH) gives me the concentration of the OH- ion.

That gives me the unknown in mols/L.

I multiply it by the molar mass, but it's wrong. What am I doing wrong?
 
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Why don't you show all your calculations?

How many OH- radicals are there in each molecule of Zn(OH)2 ?
 
OH- in the solution are NOT from the dissolved Zn(OH)2.

I would check what is the Ksp of the zinc hydroxide and use this number in the calculations.

Sadly, the question is rather ambiguous. The final result is most likely different depending on whether the pH is buffered at 8, or is 8 initially (and there is no buffering effect). Hard to say what they mean.
 
I would read that as somehow maintained at pH 8 by some means, of which the most obvious is buffering (can also be done by e.g. An automatic titrator). Unfortunately you wil meet this sort of 'lab slang' often enough. But there is still not enough information and Ksp is needed.
 

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