Unit 20 Aqueous Equilibria: Solubility Product

CHM 1046: General Chemistry and Qualitative Analysis Unit 20Aqueous Equilibria: Solubility Product Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL • Textbook Reference: • Chapter # 20 • Module # 10

SOLUBILITY RULES: • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forAg+, Pb2+,and Hg22+ salts. • All SO42- are solubleexcept forPb2+, Sr2+,and Ba2+. • All O2- are insolubleexcept forIA metalsCa2+, Sr2+,and Ba2+ salts. • 7. All OH- are insolubleexcept for IA metals, NH4+ & slightly soluble Ca 2+Ba2+& Sr2+ • 6. All salts containing the anions: CO32-, PO43-, AsO43-, S2- and SO32- are insolubleexcept fro IA metals and NH4+ salts. • 7. For salts containing the anions not mentionedabove (e.g., CrO42-, Cr2O72-, P3-, C2O42- etc.) assume that they areinsolubleexcept for IA metals and NH4+ salts, unless, otherwise informed. Cation Analysis Acid pH Basic

These reactions are governed by the basic principles of the solubility rules: AgNO3 + NaCl Precipitation Reactions AgCl + NaNO3 (aq) (aq) (s) (aq) + NaI(aq) {AgNO3+NaCl&NaI}

BaSO4(s) Ba2+(aq) + SO42−(aq) Solubility Product H2O Does BaSO4 dissolve in water? This equilibrium is that exists in a saturated solution of BaSO4 in water has an equilibrium constant expression: Ksp = [Ba2+] [SO42−] = 1.1 x 10 -10 where the equilibrium constant, Ksp, is called the solubility product.

* Table of Selected Solubility Products Constants at 25oC

Are Solubility Product (Ksp) and Solubility the Same Things? Ksp = [Ca2+] [OH−]2 = 5.5 x 10 -6 Ca(OH)2 0.823 g/L Molarity Molarity of Ions Solubility: mostly used to describe substances that dissolve very well in water Solubility Product: used for substances do not dissolve well in water Ca(OH)2 FW= 74 g/

Calculating Solubility Product (Ksp) from Solubility and vice versa Ca(OH)2 0.823 g/L Ksp = [Ca2+] [OH−]2 Molarity of Compound Solubility of Compound Molarity of Ions Ca(OH)2 FW= 74 g/ [Ca2+] = 0.0111 M Ksp = [Ca2+] [OH−]2 = (0.0111) (0.0222)2 = 5.5 x 10-6 [OH−]= 2(0.0111M) = 0.0222 M

Factors Affecting Solubility • Temperature • Common Ion Effect • pH • Complex Ions • Amphoterism

Factors Affecting Solubility: (1)Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature. H2O NaCl Na+(aq) + Cl-(aq) + Heat ΔHsoln = + 3.80 kJ/η H2O Ce2(SO4)3 2Ce3+(aq) + 3SO42- + Heat ΔHsoln = - 17 kJ/η

BaSO4(s) Na2SO4(s) Ba2+(aq) + SO42−(aq) 2Na+(aq) + SO42−(aq) Factors Affecting Solubility: (2) The Common-Ion Effect • If one of the ions in a solution equilibrium is added to a solution containing that ion, the equilibrium will shift to the left and the solubility of the salt will decrease. Ksp = [Ba2+] [SO42−] = 1.1 x 10 -10

(3) pH Factors Affecting Solubility: {Milk of Magnesia} Mg(OH)2 (s)↔ Mg2+(aq) + 2 OH –(aq) Ksp = 1.8 x 10-11 • If a substance has a basic anion, it will be more soluble in an acidic solution. Mg(OH)2 (s) + 2 H+ Mg2+(aq) + 2 H2O(l) CaCO3(s)↔ Ca2+(aq) + CO32-(aq)Ksp = 3.8 x 10-9 CO32-(aq) + H+(aq) HCO3-(aq) CaCO3(s) + H+ (aq)  Ca2+(aq) + HCO3-(aq)

Complex Ions (Coordination Compounds) Exhibit beautiful colors, are composed of two parts: (2) Several molecules &/or ions (known as Ligands) Function as Lewis bases: (1) Central metal Ion (usually a transition metal ion) Function as Lewis acids: 2+ Complex ions are extremely soluble Co2+, Cu2+, Fe3+

Factors Affecting Solubility pH and formation of Complex Ions • Complex Ions • The formation of these complex ions increases the solubility of these salts. AgCl(s)

Factors Affecting Solubility Are any of the following substances soluble? Can they be made to dissolve? Ag2O CdO Cr2O3 CoO CuO NiO FeO Fe2O3 (4) pH and formation of Complex Ions AgOH Cd(OH)2 Cr(OH)3 Co(OH)2 Cu(OH)2 Ni(OH)2 Fe(OH)2 Fe(OH)3 Solubility Rules: All O2- are insolubleexcept forIA metalsCa2+, Sr2+,and Ba2+ salts. 7. All OH- are insolubleexcept for IA metals, NH4+ & slightly soluble Ca 2+Ba2+& Sr2+ Oxides and Hydroxides of these ions are fairly insoluble But complex ions of these metals are extremely soluble. + Not very soluble Ksp = 8.0 x 10-16 Fe(OH)2 (s) Fe2+(aq) 2 OH- (aq) Add Ligand: + Fe2+ 6 CN- Fe(CN)63- (aq) Extremely soluble Kf = 1.0 x 1042

Factors Affecting Solubility • Substances with acidic cations are more soluble in basic solutions. • Metal ions can act as Lewis acids (e- pair acceptors) and formcomplex ions with Lewis bases (e- pair donors) in the solvent. pH and formation of Complex Ions (Formation Constants) Lewis Bases OH- NH3 CN- SCN- Br- S2O32- (thiosulfate)

Factors Affecting Solubility : (5) Amphoterism • Amphoteric metal oxides and hydroxides are soluble in strong acid or base, because they can act either as acids or bases. • {Amphiprotic can gain or loose electrons H+ + CO3- HCO3- H2CO3.} • Examples of Amphoteric cations are Al3+, Zn2+, and Sn2+. OH- OH- OH- OH- Al3+(aq) Al(OH)3 (s) Al(OH)43-(aq) Acid neutral ppt Base H+ H+

BaSO4(s) Ba2+(aq) + SO42−(aq) Will a Precipitate Form? At Equilibrium, Ksp = [Ba2+] [SO42−] = 1.1 x 10 -10 Problem: What is the maximum amount (grams) of BaSO4 (FW=233 g/) that will dissolve in water (saturated solution)? Molarity of Compound Solubility of Compound Molarity of Ions Ksp = [Ba2+] [SO42−] = 1.1 x 10 -10 [BaSO4] = [Ba2+] = [Ba2+] =

BaSO4(s) Ba2+(aq) + SO42−(aq) Will a Precipitate Form? At Equilibrium, Ksp = [Ba2+] [SO42−] = 1.1 x 10 -10 • In a solution, • If Q = Ksp, the system is at equilibrium and the solution is saturated. • If Q < Ksp, more solid will dissolve until Q = Ksp. • If Q > Ksp, the salt will precipitate until Q = Ksp. At non-Equilibrium conditions, Q = [Ba2+] [SO42−]

2001 Q1

At Equilibrium, Ksp = [Pb2+] [Cl−]2 = 1.6 x 10 -5

At Equilibrium, Ksp = [Ag+] [Cl−]= 1.8 x 10 -10 At Equilibrium, Ksp = [Pb2+] [Cl−]2 = 1.6 x 10 -5

2004A Q1

2002B Q5

2006A Q1

2002 B

2004 A

2005 A

2006 A

2006 (A)

Unit 20 Aqueous Equilibria: Solubility Product