Is Hydrochloric Acid Ever Basic When Diluted Infinitely?

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Discussion Overview

The discussion revolves around the behavior of hydrochloric acid (HCl) when diluted infinitely with water, specifically questioning whether such a solution can ever be considered basic. Participants explore the implications of dilution on pH and the role of water's autodissociation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that if HCl is diluted infinitely, the concentration of H+ could lead to a pH greater than 7, implying a basic solution, but questions the validity of this assumption.
  • Another participant argues that even with very low concentrations of HCl, the presence of H+ from water's autodissociation means the solution remains slightly acidic, thus challenging the idea that it could be basic.
  • A further point is raised regarding the possibility of HCl being basic if a stronger acid is used as a solvent, introducing a different context for acidity and basicity.
  • One participant acknowledges the contribution of water's ionization when adding water to HCl, suggesting that the pH would approach 7 but remain slightly acidic as more water is added.
  • There is a proposal to model the pH as a function of the volume of water added, assuming complete ionization of HCl initially.

Areas of Agreement / Disagreement

Participants express differing views on whether an infinitely diluted HCl solution can be considered basic. While some agree that the pH approaches 7, others maintain that it remains acidic due to the presence of H+ ions from water.

Contextual Notes

Participants discuss the implications of water's autodissociation and the conditions under which HCl might be considered basic, but the discussion does not resolve the complexities surrounding these concepts.

Bipolarity
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Suppose you have a HCl solution of 2.00 M
Now suppose you keep on adding water, with no limit on how much water you are adding.

We will reach a point where the HCl concentration is so low that if you take the negative log of the [H+] , you get a number greater than 7.

Doesn't this mean that we essentially have a "basic" HCl solution? But I thought that was impossible.

What's the catch here?

Thanks!

BiP
 
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Water autodissociation.
 
1) I'm not really a chemist but I am confident no. If you have such little HCl in water that the concentration of HCl is effectively zero, the H+ concentration is not zero. Water has its own self ionization that would yield ~7.

Basically this question is, is HCl basic if there is no HCl in solution? This is wrong because ANY amount of acid added on top of water is slightly more acidic than water.

2) HCl might be basic if you use an even stronger acid as a solvent. For example, sulfuric acid and nitric acid to add nitro groups.
 
Oh I forgot that if you add water you are adding both H+ and OH- due to the water's ionization.

So if you had a limited amount of HCl and added infinite water, the pH would approach 7 from the left side of the number line?

Is it possible to model the pH as a function of the volume of water added, assuming you know the concentration of the HCl initially and assuming that initially all the HCl ionizes to completion?

Thanks for your replies! This site is the best!

BiP
 
Bipolarity said:
So if you had a limited amount of HCl and added infinite water, the pH would approach 7 from the left side of the number line?

Yes.

Is it possible to model the pH as a function of the volume of water added, assuming you know the concentration of the HCl initially and assuming that initially all the HCl ionizes to completion?

Yes. See pH of a strong acid, equation 7.4 - you will just need to calculate analytical acid concentration (taking dilution into account).
 

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