Chemistry 162 Exam III General Concepts ➔ Ksp and solubility ➔ Common ion effect ➔ Q test for precipitation ➔ Selective precipitation ➔ Complex ions ➔ Coordination chemistry: complex ions, nomenclature, different forms of isomerism ➔ Thermodynamics ➔ Spontaneity ➔ Entropy ➔ Free energy ➔ Temperature dependence of K ➔ Balancing redox equations ➔ Voltaic cells ➔ Standard potentials ➔ Free energy ➔ Equilibrium constant ➔ Nernst Equation ➔ Concentration cells ➔ Batteries ➔ Corrosion ➔ Electrolysis Chapter 18 Recall from Ch. 9: Solubility Rules -- Ionic Compounds in Water ➔ A set of empirical rules that allow us to determine an ionic compound’s water-solubility ➔ Compounds were categorized as either soluble or insoluble → the truth is there are degrees of solubility ➔ Many compounds that were considered insoluble are actually sparingly soluble ➔ Soluble Exceptions Li, Na, K, NH4 None NO3, C2H3O2 None Cl, Br, I Ag, Hg2, Pb SO4 Sr, Ba, Pb, Ag, Ca ➔ Insoluble Exceptions OH, S Li, Na, K, NH4, Ca, Sr, Ba
CO3, PO4 Li, Na, K, NH4 Solubility of Sparingly Soluble Compounds -- Ksp ➔ Sparingly soluble ionic compounds ◆ All ionic compounds dissolve in water to some degree ◆ The dissolution of an ionic compound is an equilibrium process ◆ The extent of dissolution can be quantified by an equilibrium constant ◆ Example → CaF2 (s) + H2O(ℓ) ⇌ Ca2+(aq) + 2 F– (aq) ● Equilibrium constant for this reaction has a very specific name and equilibrium expression: the solubility-product constant (Ksp) ● 𝐾?? = [ 𝐶𝑎 2+] 𝒆𝒒 [ 𝐹 −] 𝒆 q ◆ Ksp is a rough measure of a compound’s solubility ● The degree a solid compound can dissociate ➔ Some Ksp values at 25 °C ◆ A large range of values ◆ Ksp can be used directly to compare solubilities of compounds ONLY when the compounds have the same dissociation stoichiometry ● The number of ions formed upon dissolution ● BaSO4 → 2 ions ● BaF2 → 3 ions ◆ To compare compounds having different dissociation stoichiometries, actual molar solubilities must be calculated Molar Solubility ➔ Solubility is the amount of solute that will dissolve in a given amount of solution ◆ At a particular temperature ➔ Molar solubility of a compound (s) ◆ Number of moles of a compound that dissolves per liter of aqueous solution ( M or mol/L ) ◆ The molar solubility (s) can be calculated from the compound’s Ksp value and values from an ICE table Dissociation Stoichiometry ➔ The exact relationship between Ksp and molar solubility depends on the dissociation stoichiometry ◆ For example → ● 3 ions : MX2 (s) → cube root ● 2 ions in MX (s) → square root ● 4 ions in MX3 (s) → fourth root
Factors Affecting Solubility ➔ Common ion effect ➔ pH ➔ Formation of complex ions The Common Ion Effect and Solubility ➔ The solubility of sparingly soluble compound will be decreased if the solution already contains a common ion ◆ When an ionic compound is added to a solution that already contains the cation or anion of the ionic compound, the compound will dissociate less and will be less soluble ◆ Example → add NaF to CaF2 → CaF2 (s) ⇌ Ca2+(aq) + 2 F– (aq) ●
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