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


by Kaede_N9
Tags: acidic, compound, h2so4
Kaede_N9
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#1
Mar8-12, 07:55 PM
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1. The problem statement, all variables and given/known data
Which compound is more acidic? (without using pkA value)

HCl or H2SO4


2. Relevant equations
Electronegativity.
Inductive effect.


3. 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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Borek
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Mar9-12, 01:34 AM
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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.
Kaede_N9
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Mar9-12, 07:22 AM
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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.

Ygggdrasil
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Mar9-12, 10:13 AM
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Which compound is more acidic? (without using pkA value) HCl or H2SO4


Also consider that resonance stabilization of the conjugate base occurs in H2SO4.
Borek
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#5
Mar9-12, 11:26 AM
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Quote Quote by Kaede_N9 View Post
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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