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Acid Strength

  1. Apr 18, 2004 #1
    Why is HSO3- a stronger acid then H2SO3?

    And also, i know that When the size of an atom X increases, the H-X bonds decreases, meaning the strength of the acid increases since more H+ are ionized.

    But when when H-X are more electronegitive, doesnt it mean the bonds between the H-X gets stronger, meaning fewer H+ ionizes?? But this is not the case, the more electrongetive the bond between H-X, the acid strength gets stronger. Is my conceptual idea wrong?

    Also, lets say you have solutions of NH3, HCl, NaOH, and HC2H3O2 , all with the same solute concetrations. How would you know rank the pH of these solutions from highest to lowest or vice versa?
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  3. Apr 18, 2004 #2
    from what I know, the pH value is a measure of concentration of H+ ions, but the strength of an acid is how easy an acid releases its hydrogen ions.
  4. Apr 19, 2004 #3
    I don't know about HSO3- and H2SO3, but if you mean HSO4 and H2SO4, then the latter is stronger.

    Increased electronegativity doesn't translate to stronger bonds.

    Of your list, HCl is the strongest acid, followed by acetic acid, ammonia, and sodium hydroxide.
  5. Apr 19, 2004 #4


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    other way around then your statement is true. im assuming you know why if that is the case.

    other way around again. your conceptual idea is wrong.

    more electronegativity of X means the bond will be more ionic, ie ionization is more favoured. therefore meaning more ionization occurs.

    electronegativity increases for X, then the acid strength increases for H-X.

    note: H-X must be binary and X must come from the same period for the above statement to hold. because otherwise various different factors will be affecting the bond instead of just a change in electronegativity.
  6. Apr 19, 2004 #5


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    Acidity also has to do with polarity of the molecule. Think transition state, of which the product is an H+ ion and the subsequent anion. A transition state with more H+ character will have lower activation energy.

    Online help with high school and college chemistry
  7. Apr 20, 2004 #6
    I think some one already said this but i'll say it again. By 'Strength' im assuming you mean ph, which is the concentration of H+ ions, therefore if an acid can easily disassociate completely more H+ ions are Formed. ie X-H -> X- + H+, but if the acid only partially disassociates not as many H+ ions are formed. X-H <=> X- + H+ (reversible reaction)
    :) that what i was told anyway.

    so one acid would be stronger if it dissasosiated into H+ions more that another.
    Last edited: Apr 22, 2004
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