Hydrogen and hydroxide concentration

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Discussion Overview

The discussion centers around the relationship between hydrogen ion concentration and hydroxyl ion concentration in water, particularly in the context of maintaining the ion product constant (KW) at 25°C. Participants explore the implications of introducing hydrogen ions and how this affects hydroxyl ion concentration, touching on concepts of chemical equilibrium and thermodynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how the concentration of hydroxyl ions changes to maintain KW when hydrogen ions are introduced, suggesting a misunderstanding of the underlying principles.
  • Another participant asserts that the maintenance of KW is a fundamental property of chemical equilibria, stating that at equilibrium, the reaction quotient equals the equilibrium constant.
  • A participant connects the discussion to Le Chatelier's principle, implying that it relates to the observed behavior of chemical systems under changes in concentration.
  • Further clarification is provided that Le Chatelier's principle also describes observed reality, reinforcing the idea that explanations follow from empirical observations.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding the mechanisms that maintain KW, with some asserting established principles while others seek clarification on the concepts involved. The discussion does not reach a consensus on the initial participant's understanding.

Contextual Notes

The discussion highlights potential misunderstandings regarding the interaction of hydrogen ions with water and hydroxyl ions, as well as the implications of chemical equilibrium principles. There are unresolved aspects concerning the specific interactions and their effects on ion concentrations.

Who May Find This Useful

This discussion may be of interest to students and individuals studying chemistry, particularly those exploring concepts of chemical equilibrium, ion concentrations, and thermodynamic principles.

nobahar
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This may not even be a valid question, as I may have misunderstood; but here goes...
At 25C, the KW of water is 1 x 10-14 If you increase the amount of hydogen ions present, why does the concentration of hydroxyl ions present alter in such a way that the KW is maintained (i.e. the product of the concentrations of hydrogen and hydroxyl ions)?
If you introduce protons, then they may associate with water to form hydroxonium ions, or they may associate with hydroxyl ions; in the first there will be an incraese in the hydrogen ion concentration, in the second there will be more water formed, which decreases the hydroxyl concentration but does not alter the hydrogen ion concentration. If it was a mixture of the two (that is, if the protons introduced interact with water both water and hroxyl ions), I still can't see how the two concentrations would be balanced so that the KW is maintained.
No textbooks seem to give a reason, which suggests I've misunderstood. Can someone help me with this? :blushing:
 
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nobahar said:
why does the concentration of hydroxyl ions present alter in such a way that the KW is maintained

Because that's exactly the way it works?

All chemical equilibria have the same property - at equilbrium reaction quotient equals equilbrium constant. It can be explained in thermodynamical terms (using chemical potentials), it can be explained in kinetic terms (using speeds of forward and backward reactions) - but in fact both explanations just follow the observed reality.

Reality was first, explanations are later :smile:

--
 
Am I right in saying that this ties in with Le Chatelier's principle, then?
 
Yes, just remember that Le Chatelier's principle also describes reality as it was observed.

--
 
Thankyou Borek.
 

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