K and Salt Solubility

Learning Goals

You will now learn how to estimate the solubility of a salt from the experimental Ksp and how to determine relative solubilities from the Ksp values.


This section just reverses the logic application from the previous section. For the hypothetical salt we again have the equilibrium AaBb aA+ + bB-. Now we say that if the solubility of the salt is x, then the equilibrium concentration of A+ is ax and the equilibrium concentration of B- is bx so that we can write Ksp = [ax]a[bx]b. Putting in the known value of Ksp and the stoichiometric coefficients we can then calculate x, the solubility of the salt.

We can also calculate the relative solubilities of a set of salts from the solubility product constants, but only if each member of the set has the same ion ratios. You should be able to understand this restriction by carefully looking at the previous paragraph on calculating solubilities from Ksp values. For salts of the same ion ratios, the larger the Ksp, the more soluble the salt.

Review Question

  1. Calculate the solubility of AuI3 from the Ksp constant given in Appendix J. Now calculate the concentration of the ions and compare to the review question of the previous section.
  2. Work Exercise 19.6 on page 884 in your text.


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