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Solubility of fluorides

  1. May 17, 2015 #1
    1. The problem statement, all variables and given/known data
    The fluoride which is most soluble in water is:
    a)CaF2
    b)BaF2
    c)SrF2
    d)BeF2

    2. Relevant equations
    none

    3. The attempt at a solution
    the answer given is D.
    but BeF2 is covalent in nature and is soluble in organic solvents.
    Due to more electropositivity of Ba, BaF2 will have more ionic nature. On the other hand, since F is smaller compared to Ba, according to Fajan's rule, it can easily polarize Ba and it will have more covalent nature.
    So i am confused about option C.
     
  2. jcsd
  3. May 17, 2015 #2

    James Pelezo

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    Gold Member

    Beryllium Fluoride's water solubility in most MSDS documents is defined as highly soluble in water with no specific saturation values given. The other compounds in the answer choice list all have published Solubility Product Constants (Ksp-values) ranging from 10-7 to 10-9. This, of course, is 'elimination logic' based on the low solubility of the the first three choices, BeF2 is the only option remaining without a published Ksp value. .
     
  4. May 25, 2015 #3
    [My thinking] Since Be and F both are small in size , their hydration enthalpies should be high. Therefore the solubility of this compound should be considerable.
    And for the others we should see the point of view of the electron robber flourine. The bigger cations can easily give their electrons as their ionisation energies are low...so why would flourine leave them to go free in water?
    It has what it wants....electrons.
     
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