[Gargamel]

I wonder why NaCl can easily dissolve in water meaning a high K_sp, while fx AgCl have a very low K_sp and can not dissolve to the same extent as NaCl

I know that water is polar, and to me it seems all ioncompounds should dissolve, but i cant understand why some salts cant.

Can someone please help?

[adnan]

This depends on extent of ionization caused by water molecules. The extent of ionization of AgCl is lesser. So, Ksp is also lesser.This is because water molecules fail to break the ionic bond between Ag+ an Cl- due to high lattice energy.

[Gargamel]

Thx for the answer.

Hmm...Im not sure you convince me.

AgCl melting point and boiling point is 457^oC and 1547^oC   (http://en.wikipedia.org/wiki/Silver_chloride)
NaCl melting point and boiling point is 801^oC and 1465^oC   (http://en.wikipedia.org/wiki/Nacl)

It seems to me they have quite similar lattice energy, unless I for some reason cant look at the melting and boiling points.

Is this the hole explanation you gave me adnan?

[renge ishyo]

The extent of ionization caused by the water molecules is greater for NaCl, because Na has empty D-orbitals that the water molecules can complex to. These additional interactions help offset the energy loss from breaking the otherwise strong sodium chlorine bond. In contrast, silver's d-orbitals are mostly filled with electrons and as a result less ions can complex with silver to offset the silver chloride bond. So less silver chloride dissolves. If you evaporate out the water they both will crystalize into solid salts so you know that the water is the main driving force affecting the separation in either case.

[adnan]

You cant relate the lattice energy with melting points. Lattice energy is to convert the ionic compounds into its gaseous ions.And solubility depends on lattice energy and hydration energy of ionic compounds.If the hydration energies of the gaseous ions are more exothermic than the negative of the lattice energy, then the enthalpy of solution will be negative and the substance will dissolve.

i think this will help you.
http://home.clara.net/rod.beavon/solubility.htm

[Suleman]

To be more simple

Solubility of ionic compound depends on two things

1) Lattice Energy  --->  Proportional to the binding force between Na & Cl
2) Hydration Energy ----> Proportional to the force of separation on Na and Cl exerted by water molecules!


Keeping the Hydration energy constant a particular salt will be dissolved easily by water if its lattice energy is low as comparable to salt whose lattice energy is more!


But solubility solely does not depends on lattice energy but also on hydration energy. Keeping the Lattice ENERGY CONSTANT a salt will be more soluble if its Hydration energy is more!

simply if

hydration energy - Lattice energy = more positive than the salt will be dissolved more easily

In case of NaCl and AgCl.

If
X= hydration energy - Lattice energy --->For NaCl

and
Y = Hydration energy -Lattice energy --> for AgCl

than

X > Y

it means Nacl will be dissolved with ease as its energies difference is more positive!