Solubility and Ksp

Solid silver chromate is added to pure water at 25 °C, and some of the solid remains undissolved. 

The mixture is stirred for several days to ensure that equilibrium is achieved between the undissolved Ag2Cr04(s) and the solution. Analysis of the equilibrated solution shows that its silver ion concentration is 1.3 X 10 M. Assuming that the Ag2Cr04 solution is saturated and that there are no other important equilibria involving Ag or Cr04 ions in the solution, calculate X for this compoimd. 

Analyze We are given the equilibrium concentration of Ag in a saturated solution of Ag2Cr04 and asked to determine the value of for Ag2Cr04. 

To calculate X, we need the equilibrium concentrations of Ag and Cr04 . We know that at equilibrium [Ag ] = 1.3 X 10 M. AU the Ag and Cr04 ions in the solution come from the Ag2Cr04 that dissolves. Thus, we can use [Ag ] to calculate [Cr04 ]. 

Solve From the chemical formula of silver chromate, we know that there must be two Ag ions in solution for each Cr04 ion in solution. Consequently, the concentration of CrO/ is half the concentration of Ag  

Write the expression for the solubility-product constant for Cap2, and look up the corresponding Ksp value in Appendix D. 

Analyze We are asked to write an equilibrium-constant expression for the process by which Cap2 dissolves in water. 

Plan We apply the general rules for writing an equilibrium-constant expression, excluding the solid reactant from the expression. We assume that the compound dissociates completely into its component ions  

Give the solubility-product-constant expressions and values (from Appendix D) for (a) barium carbonate, (b) silver sulfate. 

It is important to distinguish carefully between solubility and the solubility-product constant. The solubility of a substance is the quantity that dissolves to form a saturated solution. (Section 13.2) Solubility is often expressed as grams of solute per liter of Solution (g/L). Molar solubility is the number of moles of solute that dissolve in forming 1 L of saturated solution of the solute (mol/L). The solubility-product constant (K p) is the equilibrium constant for the equilibrium between an ionic solid and its saturated solution and is a unitless number. Thus, the magnitude of is a measure of how much of the solid dissolves to form a saturated solution. 

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A. K. Sawyer, Solubility and Ksp of Calcium Sulfate A General Chemistry Laboratory Experiment, J. Chem. Ed 1983,60, 416. 

Reorganize the discussion of solubility. We start with solubility and Ksp for a single solute in solution and go on to the effect of fCjp on reactions. 

Solubility Product Constant, Kjp 18-2 Relationship Between Solubility and Ksp... 

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