EN and solubility

[rtmcad2319]

---

Members do not see this ad.

Who knows how to relate electronegativity to solubility?

In the PrincetonReview Book they ask a question about Na+ and Ag 2+ and the answer is that Ag2+ is less soluble due to its higher electronegativity?

I do not understand the correlation?

Thank you kindly!

 

[tsazmand]

Generally polar solute molecules will dissolve in polar solvents and non-polar solute molecules will dissolve in non-polar solvents. The polar solute molecules have a positive and a negative end to the molecule. If the solvent molecule is also polar, then positive ends of solvent molecules will attract negative ends of solute molecules. This is a type of intermolecular force known as dipole-dipole interaction. All molecules also have a type of intermolecular force much weaker than the other forces called London Dispersion forces. The higher the EN the higher the Dipole Dipole interaction (the higher the solubility). Thats what i learned so i would think Ag+2 woulb have a >er solubility.

Another approach is that Ag2+ has a lower solubilty b/c the dipole interactions would be harder to overcome

 

[rtmcad2319]

Anyone else have an idea on this one?

Na+ is definitly more soluble

 

[QofQuimica]

Who knows how to relate electronegativity to solubility?

In the PrincetonReview Book they ask a question about Na+ and Ag 2+ and the answer is that Ag2+ is less soluble due to its higher electronegativity?

I do not understand the correlation?

Thank you kindly!

This question is way beyond the level of understanding that you need for MCAT-level general chemistry, so don't freak out about it. At freshman level, it is enough to simply memorize the salt solubility trends. You can take inorganic chemistry if you want to learn more about this subject.

The easiest way to understand the relative solubilities of Ag+ salts versus Na+ salts is called hard/soft acid base theory. Na+ (and other group I cations) are "hard", meaning that they tend to be small, and not easily polarizable (their electron clouds don't shift around much). Transition metal cations like Ag+ are "soft", meaning that they tend to be larger, and they have polarizable electron clouds. (You can kind of imagine that soft acids like Ag+ have sloppy electron clouds that shift around, while hard acids like Na+ have "stiffer" electron clouds that can't move much.)

The reason why this matters is that water is a hard base. (I am assuming that you are talking about water solubility here, so if you aren't, this explanation won't necessarily hold!) You probably learned in your organic class that "like dissolves like", and the same is true for hard acids and hard bases: they prefer each other over pairing up with a soft acid or base. So since water is a hard base, it will prefer the hard acid (Na+) over the soft acid (Ag+). Other solvents that are soft bases, like benzene, would be predicted to have the opposite solubilizing effects on these cations.

So how does this relate to electronegativity? In general, IONS with high electronegativity tend to be hard, while those with low electronegativity tend to be soft. It is true that NEUTRAL Na atoms have a low electronegativity; however, Na+ IONS have a relatively high electronegativity, much higher than Ag+ ions. (This is logical if you consider another periodic trend that is closely related to electronegativity: the ionization energy. You can imagine that it is much easier to remove a second electron from the 4d orbitals in Ag+ than it is to remove one of the 2p electrons from Na+ ions!!!)

Hope this helps.