Which compound is more acidic? (without using pkA value) HCl or H2SO4

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Discussion Overview

The discussion revolves around the acidity of HCl and H2SO4, specifically comparing their acidic strength without referencing pKa values. Participants explore concepts such as electronegativity and inductive effects to justify their claims.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that H2SO4 is more acidic than HCl due to sulfur's higher electronegativity compared to chlorine, but questions the validity of using inductive effects to support this claim.
  • Another participant expresses uncertainty about the definition of acidity, proposing that it could refer to acid strength or the ability to neutralize bases, leading to different conclusions regarding HCl and H2SO4.
  • A participant notes that H2SO4 has a lower pKa than HCl, but emphasizes the desire to avoid using pKa values in their reasoning.
  • Another point raised is the resonance stabilization of the conjugate base in H2SO4, which may contribute to its acidity.
  • There is mention of varying pKa values from different sources, indicating inconsistency in the literature regarding the acidity of these compounds.

Areas of Agreement / Disagreement

Participants do not reach a consensus on which compound is more acidic, as differing definitions of acidity and varying interpretations of the evidence lead to multiple competing views.

Contextual Notes

Participants acknowledge limitations in their reasoning, such as the dependence on definitions of acidity and the challenge of comparing electronegativity and inductive effects without definitive conclusions.

Kaede_N9
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Homework Statement


Which compound is more acidic? (without using pkA value)

HCl or H2SO4


Homework Equations


Electronegativity.
Inductive effect.


The Attempt at a Solution


Since sulfur is more electronegative compared to cholrine, H2SO4 is more acidic than HCl...
So then I think of how I could use inductive effect instead of electronegativity to verify this claim.

Since sulfur is more electronegative compared to oxygen it shall pull away electrons slightly, more than chlorine on hydrogen?
I don't think it'll work since there are a 3 oxygens around sulfur and so the combined electronegativity outweighs that of sulfur?

What do you think?
 
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I think I have no idea what it means to be "more acidic". And I am deadly serious, I am not aware of any definition of acidity. The way I see it it can mean one of two things - acid strength (in which case HCl is "more acidic"), or ability to neutralize base (similarly to alkalinity) - in which case H2SO4 as diprotic is more acidic.

Poorly worded question.
 
Original question:
For the following pairs of compounds, predict which one will be the strongest acid
and justify your choice.

Answer:
Between HCl and H2SO4, H2SO4 has a lower pKa (~-9) than HCl (~7) and so it is a stronger acid compared to HCl.

I wanted to answer this question without using a pKa table so I tried comparing the electronegativity of the central atoms, and as wel as their inductive effects. Not sure if inductive effect would work though.
 
Also consider that resonance stabilization of the conjugate base occurs in H2SO4.
 
Kaede_N9 said:
Between HCl and H2SO4, H2SO4 has a lower pKa (~-9) than HCl (~7)

Apparently it depends on the source used. Kotrly & Sucha (Handbook of Chemical Equilibria in Analytical Chemistry) list sulfuric acid pKa1 as -3, Hulanicki (Reactions of acids and bases in analytical chemistry) lists pKa of HCl as -4.
 

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