Samiamm
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Dissociating
Why do ionic compounds dissociate whereas molecular compounds do not. Also, why do some compounds (strong acids/bases) COMPLETELY dissociate whereas
other compounds (weak acids/bases) PARTIALLY dissociate??
I'm making a study guide for chapter 4 of my chem class, and, I like to be very thorough, and when I came to this part, I figured out I understand why
some things dissolve and dissociate but not why somethings FULLY dissociate whereas other PARTLY dissociate and that I was only memorizing what does
and does not fully dissociate
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blogfast25
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Did you mean 'dissociate when dissolved in a suitable solvent'?
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Samiamm
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yes
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Nicodem
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Thread Moved
29-9-2012 at 23:01 |
weiming1998
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Quote: Originally posted by Samiamm  | Why do ionic compounds dissociate whereas molecular compounds do not. Also, why do some compounds (strong acids/bases) COMPLETELY dissociate whereas
other compounds (weak acids/bases) PARTIALLY dissociate??
I'm making a study guide for chapter 4 of my chem class, and, I like to be very thorough, and when I came to this part, I figured out I understand why
some things dissolve and dissociate but not why somethings FULLY dissociate whereas other PARTLY dissociate and that I was only memorizing what does
and does not fully dissociate |
Ionic compounds are basically a lattice of cations and anions. For example, sodium chloride is Na+ and Cl- stacked together. There is virtually no
attraction between the extra electron in the chloride ion and the Na+ ion. So they exist, stacked next to each other, the extra electron being
confined to the chloride ion. When a suitable solvent is utilised, the solvent breaks apart the ionic lattice, allowing the ions to exist separately
in solution. As there are no attraction between the extra electron in Cl- and Na+, this could happen.
For molecular compounds, here is an example. Water. The electrons in water generally hangs around the oxygen, although there is still some attraction
between the electrons and the hydrogen. Because of that, it cannot dissociate to a significant extent, since the attraction between the electrons and
hydrogen is too strong, and dissociation will just lead to the attraction between the H+ and the OH-, giving the hydrogen back the electron. Also
because of this attraction, water molecules clump together because the electron-deficient hydrogen ends on a water molecule becomes attracted to the
electron-rich oxygen centre on another water molecule. This is why molecular compounds cannot dissociate to any significant extent.
The same thing applies to strong and weak acids. In a solvent (let's just use water for an example) the hydrogen on a strong acid is far more
attracted to the electron-rich centre of a water molecule than the anion that the hydrogen is bonded to. So the molecule breaks apart, the hydrogens
in the strong acid molecules becoming attached to the centres of water molecules, forming H3O+.
But for a weak acid, it's different. Although the hydrogen ions are still more attracted to the electron-rich centres of water molecules, they are
also reasonably attracted to the anion that it is bound to. As more acid molecules dissociate, the access of the hydrogen ions to the electron-rich
centres of water molecules gets lesser and lesser (because there's less H2O, as opposed to H3O+). Eventually, the acid molecules stops dissociating,
because the attraction of the hydrogen to the water molecules is not strong enough to break apart the molecule, due to the acid and water molecule
being too far apart. Thus, a mix of hydrogen ions, the leftover anions, and undissociated acid molecules are present.
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Samiamm
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Thanks for your reply, it greatly helped me, I learned it also has a lot to do with equilibrium
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