Chem Exam III - Chemistry 162 Exam III General Concepts Ksp and solubility Common ion effect Q test for precipitation Selective precipitation Complex

Chem Exam III - Chemistry 162 Exam III General Concepts Ksp...

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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
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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
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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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