Solubility Product

  1. Why is Ksp not defined for soluble salts? Also, when an equilibrium is established between the solid, undissolved salt and the ions in the saturated solution, won't adding more solid shift the equilibrium to the left causing more ions to form?
     
  2. jcsd
  3. Le Chatelier's Principle:
    Of course, when the solution is saturated, adding salt isn't going to change the concentration. The salt just piles up with the rest at the bottom of the beaker. The equilibrium of the solution has not been changed.

    If you look at the interface between the solid and solution, you have created more opportunity for both the solution to precipitate and for precipitate to redissolve.
     
  4. Borek

    Staff: Mentor

    It is perfectly valid for every salt.

    Please remember that "soluble" and "insoluble" is not a precise classification. Every salt is in a way soluble - some are better soluble, some are less soluble, and in each case we can describe the solubility with the Ksp.

    In practice it doesn't make much sense to use Ksp for highly soluble salts, because of thermodynamic effects which make calculations difficult (high ionic strength of the solution means we have problems evaluating activity coefficients). But the approach is still perfectly valid.
     
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