Why is the concentration of [OH-] not equal to the square root of Kw?

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Discussion Overview

The discussion revolves around the calculation of hydroxide ion concentration, [OH-], from the ion product of water, Kw, specifically at a temperature of 50°C. Participants explore the conditions under which the square root of Kw can be used to determine [OH-], considering the context of pure water versus other potential solutions.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that taking the square root of Kw should yield the concentration of [OH-], using the value of Kw at 50°C.
  • Another participant points out that this approach is valid only for pure water, implying that additional context may affect the calculation.
  • A participant questions whether the lack of additional information in the problem affects the calculation of [OH-].
  • One participant reiterates the definition of Kw as the product of [H+] and [OH-], suggesting that if [H+] equals [OH-], then [OH-] can indeed be calculated as the square root of Kw.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the square root of Kw can be applied in this scenario without additional information. There is uncertainty regarding the implications of "the above solution" and whether it affects the calculation.

Contextual Notes

The discussion highlights the assumption that [H+] equals [OH-] in pure water, but does not resolve how other factors might influence the calculation of [OH-] in different solutions.

disneychannel
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So I thought if I have the value of Kw and I need to find the concentration of [OH-] then all I would have to do is square root the Kw. But in this example, it is not the case why?

Kw at 50oC is 5.48x10-14. Calculate OH- concentration

so i just square rooted 5.48x10-14 and got 2.34 x10-7. Shouldn't this be right?
 
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For a pure water at 50°C that would be a correct approach. Is there some additional information in the question?
 
No. It just states "calculate the [OH] concentration from the above solution at 50 degrees" But, I am pretty sure that would not make a difference. Correct?
 
disneychannel said:
No. It just states "calculate the [OH] concentration from the above solution at 50 degrees" But, I am pretty sure that would not make a difference. Correct?

What is "the above solution"?
 
Kw= [H+][OH-] by definition.
If [H+]=[OH-] then [OH-]=Sqrt (Kw)
 

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