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

  1. 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?
     
  2. jcsd
  3. Borek

    Staff: Mentor

    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.
     
  4. 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.
     
  5. Ygggdrasil

    Ygggdrasil 1,651
    Science Advisor

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

    Staff: Mentor

    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.
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?
Similar discussions for: Which compound is more acidic? (without using pkA value) HCl or H2SO4
Loading...