Chapter 13 Reaction Rates and Chemical Equilibrium 13.6 Equilibrium in Saturated Solutions Learning Goal Write the solubility product expression for a slightly soluble salt and calculate the Ksp; use Ksp to determine the solubility. © 2014 Pearson Education, Inc.

Equilibrium Systems in Solutions Equilibrium systems also include aqueous saturated solutions between solid solutes of slightly soluble salts and their ions, such as a slightly soluble salt such as calcium phosphate Ca3(PO4)2, found in bones Ca3(PO4)2(s) 3Ca2+(aq) + 2PO43−(aq) a slightly soluble salt such as calcium oxalate CaC2O4, found in kidney stones CaC2O4(s) Ca2+(aq) + C2O42−(aq) © 2014 Pearson Education, Inc.

In a saturated solution Solubility Product In a saturated solution a solid, slightly soluble salt is in equilibrium with its ions at constant temperature, the concentration of the ions in the saturated solution is constant Calcium oxalate, a slightly soluble salt, produces small amounts of Ca2+ and C2O42− in aqueous solution. © 2014 Pearson Education, Inc.

CaC2O4(s) Ca2+(aq) + C2O42−(aq) Ksp = [Ca2+][C2O42−] Solubility Product The solubility of a salt is the quantity that dissolves to form a saturated solution, represented by Ksp. CaC2O4(s) Ca2+(aq) + C2O42−(aq) Ksp = [Ca2+][C2O42−] Ca3(PO4)2(s) 3Ca2+(aq) + 2PO43−(aq) Ksp = [Ca2+]3[PO43−]2 © 2014 Pearson Education, Inc.

Write a Ksp expression for the slightly soluble salt, Ag2CO3(s). Learning Check Write a Ksp expression for the slightly soluble salt, Ag2CO3(s). © 2014 Pearson Education, Inc.

Write a Ksp expression for the slightly soluble salt, Ag2CO3(s). Solution Write a Ksp expression for the slightly soluble salt, Ag2CO3(s). Write the solid salt on the left and the aqueous ions on the right: Ag2CO3(s) 2Ag+(aq) + CO32− (aq) The solubility product expression is written as the product of the molar concentration of the ions. Ksp = [Ag+]2[CO32−] © 2014 Pearson Education, Inc.

Solubility Product Constant The numerical value of the solubility product expression is the solubility product constant, Ksp. Solubility is expressed as the molar solubility, which is the moles of solute that dissolve in 1 liter of saturated solution. © 2014 Pearson Education, Inc.

Guide to Calculating Ksp © 2014 Pearson Education, Inc.

Learning Check We can make a saturated solution of CaCO3 by adding solid CaCO3 to water and stirring until equilibrium is reached. What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains and © 2014 Pearson Education, Inc.

What is the numerical value of Ksp for CaCO3 if Solution What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains Step 1 State the given and needed quantities. © 2014 Pearson Education, Inc.

What is the numerical value of Ksp for CaCO3 if Solution What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains Step 2 Write the equilibrium equation for the dissociation of the slightly soluble salt. © 2014 Pearson Education, Inc.

What is the numerical value of Ksp for CaCO3 if Solution What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains Step 3 Write the solubility product expression (Ksp). © 2014 Pearson Education, Inc.

What is the numerical value of Ksp for CaCO3 if Solution What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains Step 4 Substitute the molar concentration of each ion into the Ksp expression and calculate. © 2014 Pearson Education, Inc.

Solubility Product Constants © 2014 Pearson Education, Inc.

The molar solubility, S, of a slightly soluble salt is the number of moles of solute that dissolves in 1 liter of solution for example, the molar solubility of CdS, is found experimentally to be If we know the Ksp, we can determine the molar solubility. © 2014 Pearson Education, Inc.

Guide to Calculating Molar Solubility from Ksp © 2014 Pearson Education, Inc.

Calculate the molar solubility, S, of CdS if it has a Learning Check Calculate the molar solubility, S, of CdS if it has a Cadmium sulfide is a slightly soluble salt. © 2014 Pearson Education, Inc.

Calculate the molar solubility, S, of CdS if it has a Solution Calculate the molar solubility, S, of CdS if it has a Step 1 State the given and needed quantities. © 2014 Pearson Education, Inc.

Calculate the molar solubility, S, of CdS if it has a Solution Calculate the molar solubility, S, of CdS if it has a Step 2 Write the equilibrium equation for the dissociation of the slightly soluble salt. © 2014 Pearson Education, Inc.

Calculate the molar solubility, S, of CdS if it has a Solution Calculate the molar solubility, S, of CdS if it has a Step 3 Write the solubility product expression, Ksp, using S. © 2014 Pearson Education, Inc.

Calculate the molar solubility, S, of CdS if it has a Solution Calculate the molar solubility, S, of CdS if it has a Step 4 Calculate the molar solubility S. © 2014 Pearson Education, Inc.

Solubility, Adding a Common Ion When MgCO3, a slightly soluble salt, dissolves in water, small amounts of Mg2+ and CO32− ions are produced in equal amounts. The Ksp and molar solubility for MgCO3 are: © 2014 Pearson Education, Inc.

Solubility, Adding a Common Ion When we add a soluble salt, MgCl2 to the solution, it dissolves into Mg2+ and 2Cl− ions, increases the concentration of Mg2+ in the solution, and shifts the equilibrium of the reaction to the left, decreasing the amount of ions produced. MgCO3(s) Mg2+(aq) + CO32−(aq) Mg2+ added © 2014 Pearson Education, Inc.

Solubility, Adding a Common Ion When we add a soluble salt, Na2CO3 to the solution, it dissolves into 2Na+ and CO32− ions, increases the concentration of CO32− in the solution, and shifts the equilibrium of the reaction to the left, decreasing the amount of ions produced. MgCO3(s) Mg2+(aq) + CO32−(aq) CO32− added © 2014 Pearson Education, Inc.

Indicate the shift in equilibrium of each change: Learning Check Indicate the shift in equilibrium of each change: PbSO4(s) Pb2+(aq) + SO42−(aq) toward products 2) toward reactants adding SO42− adding Pb2+ © 2014 Pearson Education, Inc.

Indicate the shift in equilibrium of each change: Solution Indicate the shift in equilibrium of each change: PbSO4(s) Pb2+(aq) + SO42−(aq) toward products 2) toward reactants adding SO42− 2) toward reactants adding Pb2+ 2) toward reactants © 2014 Pearson Education, Inc.

A. increases the solubility of the salt Learning Check Adding a common ion to a saturated solution of a slightly soluble salt has what effect on the solubility product expression, Ksp? A. increases the solubility of the salt B. does not change the solubility of the salt C. decreases the solubility of the salt © 2014 Pearson Education, Inc.

C. decreases the solubility of the salt Solution Adding a common ion to a saturated solution of a slightly soluble salt has what effect on the solubility product expression, Ksp? C. decreases the solubility of the salt © 2014 Pearson Education, Inc.

Concept Map © 2014 Pearson Education, Inc.