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Hard soft acid base

  1. Jun 13, 2015 #1
    Hi guys, my name is ferdinand. I'm curious about HSAB, especially to predict where the reaction goes.
    Exp: HI + NaF >>> HF + NaI
    H is hard acid
    I IS soft base
    Na is hard acid
    F is hard base, and

    HF Is hard.hard
    NaI Is hard soft.
    The reaction will goes to right or left? And why?
    And since hard acid like to bind hard base, why NaI formed?
    Thank you...
    Terima kasih.


    And how about the borderline? Is it count as hard or soft?
     
  2. jcsd
  3. Jun 15, 2015 #2
    Have you calculated the equilibrium constant? My quick look says the reaction goes to the left, as you suspect.
     
  4. Jun 15, 2015 #3

    Borek

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    Staff: Mentor

    In water? Or a solid and a gas?
     
  5. Jun 15, 2015 #4
    Good question. I assumed water. OP?
     
  6. Jun 15, 2015 #5

    Borek

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    Staff: Mentor

    Then it should go to the right, HF is a weak acid.
     
  7. Jun 15, 2015 #6
    I used DeltaGf of (all aqueous at 25C):
    -129 kcal/gmol for NaF
    -71 for NaI
    -12 for HI
    -66 for HF

    and got DeltaGrxn = +4kcal/gmol and using DeltaG = -RTlnKeq, got Keq = 1.2E-3 indicating left side reactants at higher concentrations than right side products.
     
    Last edited: Jun 15, 2015
  8. Jun 16, 2015 #7

    Borek

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    Staff: Mentor

    Well, it depends on what your starting material is. Yes, in general the equilibrium is to the left, but if you add HI to the NaF solution, fluoride gets protonated and the shift is to the right.
     
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