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

Kaede_N9

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?

Borek

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

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

Also consider that resonance stabilization of the conjugate base occurs in H2SO4.

Borek

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.