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Posted by on Thursday, May 8, 2014 at 7:54pm.

So I am trying to understand in molecular terms the solubility of NaCl in water.

So there are intramolecular forces that are mostly ionic between the ions, creating this partial positive, partial negative substance. And the intermolecular forces are also ionic. Ionic forces are the strongest of the intermolecular forces, right?
So if this is the case, why does NaCl dissolve in water because the hydrogen bonds shouldn't be strong enough to break the ionic bonds. Is it because there are so many hydrogen bonds that they end up breaking the single ionic bond?

Thanks!

  • Chemistry - , Thursday, May 8, 2014 at 8:00pm

    take a look at charge - dipole attraction

    http://www.chem.ufl.edu/~itl/4411/lectures/lec_g.html

  • Chemistry - , Thursday, May 8, 2014 at 8:01pm

    One major correction. It is true that the intermolecular forces (the water molecules pulling at the lattice energy) but those are ion-dipole forces and not ionic. Charged yes but not ionic).
    The answer to your question is that youmust take into account the energy gained when the Na^+ and Cl^- are broken away from each other then they can form the hydrated ions, Na^+(aq) and Cl^-(aq). Those formations are exothermic while the forces to break the lattice bonds in the crystal are endothermic. The extra oomph NaCl needs to dissolve comes from those hydrated ions.

  • Chemistry - , Thursday, May 8, 2014 at 8:08pm

    I'm still a little bit unsure. The website didn't really specify why the ions disassociate with each other and associate with hydrogen bonding

  • Chemistry - , Thursday, May 8, 2014 at 8:18pm

    Ok, I think I get it. Thank you both very much!

  • Chemistry - , Thursday, May 8, 2014 at 8:48pm

    Look at it this way. The dipoles from the H2O molecules attract the Na^+ and Cl^- and pull on them. That's the pull to disrupt the crystal lattice energy. And it isn't a one step here to disrupt the crystal lattice and then another step to form the hydrates. It's the total energy of the disruption of the lattice energy + the energy gained by the formation of the hydrates and that total is positive so the "reaction" can take place.

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