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#Post#: 1044--------------------------------------------------
CaF2 and CaCl2
DIR By: Michel
Date: November 2, 2012, 6:02 pm
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This is not chemistry I do normally, I've been curious why CaF2
is very insoluble in water while CaCl2 is very soluble. Can
anyone tell me/explain to me the reasons why this is so?
#Post#: 1046--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: Shiva
Date: November 3, 2012, 1:08 pm
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Well, the solubility of Ionic compounds mainly depends on (i)
Lattice energy (ii) Hydration energy
In the case of Alkaline earths, hydration of ions decreases as
we go down the group. The solubility of most of the alkaline
earth salts will decrease as we go down the group whereas the
opposite happens in the case of Fluorides and hydroxides since
lattice energy of these anions are very small. Hence, even the
small difference in the size of cations make such a big
difference in the solubility. However in the case of sulfates,
the anion itself is big and it does not make much difference
even there is small change in the size of the cations. Hence,
the lattice energy overcomes the opposite trend and the
solubility of Fluorides and hydroxides increases as we go down
the group. Hope this is clear.
Shiva
#Post#: 1052--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: Michel
Date: November 5, 2012, 4:33 pm
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Thank you for your reply. Although I'm still not sure about
this, I have more questions I will post later when I have the
time to think more clearly on this.
#Post#: 1499--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: Michel
Date: December 9, 2012, 9:20 pm
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Somehow I still find it difficult to understand why the
fluorides of the alkali earths are highly insoluble...is it
mainly due to the size of the F- ion, compared to the other
halide ions? And then why could the effect be so much
pronounced?
#Post#: 1504--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: hkar19
Date: December 10, 2012, 4:51 am
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i think because the lattice bond in the F- structure and the
bond length.
The cations and the anions bond strongly, so they won't let
anything to disturbs the bonds.
so the bond is so strong!
#Post#: 1533--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: Michel
Date: December 11, 2012, 12:31 am
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--- Quote from: hkar19 link ---
>
> i think because the lattice bond in the F- structure and the
bond length.
> The cations and the anions bond strongly, so they won't let
anything to disturbs the bonds.
>
> so the bond is so strong!
>
--- End Quote ---
dosen't quite sound like the answer:-/
Anyone with more ideas??
#Post#: 2212--------------------------------------------------
Re: CaF2 and CaCl2
DIR By: Potla
Date: February 26, 2013, 12:41 pm
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Continuing on Shiva's post, the strong Ca - F bond is due to the
similar sizes of the constituent ions. From wikipedia, it seems
that F- is about 119 pm and Ca+2 is about 114 pm, whereas Cl-
is 167 pm. Similar-sized atoms form stable lattices, and so are
reluctant to go into water to form solutions.
I wonder if that's sufficiently reasonable. :)
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