Chap_19

# Chap_19 - Chapter 19 Solubility and Simultaneous Equilibria...

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337 Chapter 19 Solubility and Simultaneous Equilibria In this chapter we extend our discussion of ionic equilibria to deal with salts that until now we have consid- ered insoluble. As you learn here, such compounds do dissolve slightly and their saturated solutions represent situations in which the solid salt is in equilibrium with its ions in solution. Among the topics we examine are the effects of one salt on the solubility of another and how relative degrees of insolubility permit separation of metal ions by selective precipitation. We also study equilibria in the formation of substances called complex ions and how such substances can influence the solubilities of salts. This is a topic that has many practical ap- plications. Learning Objectives Throughout your study of this chapter, keep in mind the following objectives. 1 To learn how to write the special equilibrium law for a sparingly soluble (i.e., very slightly soluble) salt, namely, an equation for a solubility product constant or K sp . 2 To learn how to calculate the value of K sp from solubility data. 3 To learn how to calculate the solubility of a sparingly soluble salt, given its K sp value. 4 To learn the common ion effect and how it affects the solubility of some solute. 5 To learn how to calculate the solubility of a sparingly soluble salt in the presence of a common ion. 6 To learn how to use K sp to find out if the precipitation of a sparingly soluble salt will take place when a solution develops a certain composition. 7 To learn what happens chemically when metal sulfides or oxides dissolve in aqueous so- lutions. 8 To learn how a special solubility product constant, the acid solubility product constant or K spa , works best with sparingly soluble sulfides of metal ions. 9 To learn how to adjust the pH of a solution so that selective precipitation can be used to separate one metal ion from another. 10 To learn the vocabulary of complex ions and how to represent the equilibria involving metal ion complexes in solution. 11 To learn how to write appropriate chemical equations and equilibrium laws that corre- spond to formation constants and instability constants for complexes 12 To be able to apply Le Châtelier's principle to explain how complex ion formation affects the solubility of a sparingly soluble salt. 13 To learn how to use a formation constant (or its reciprocal, an instability constant) to cal- culate the effect of complex ion formation on the solubility of a sparingly soluble salt.

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338 Solubility and Simultaneous Equilibria 19.1 An insoluble salt is in equilibrium with the solution around it Review The equilibrium law for the solubility equilibrium of a salt involves the salt’s ion product, which is the prod- uct of the ion molarities raised to powers obtained from the subscripts in the salt’s formula. The sparingly sol- uble salt calcium phosphate, Ca 3 (PO 4 ) 2 , for example, gives the following equilibrium in its saturated aqueous solution.
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Chap_19 - Chapter 19 Solubility and Simultaneous Equilibria...

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