chapter 15
What does the solubility product constant (Ksp) describe? | The equilibrium between an undissolved ionic solid and its ions in a saturated solution.
What type of system does Ksp apply to? | Sparingly soluble ionic solids in water.
Write the general dissolution reaction for an ionic solid. | MpXq(s) ⇌ pMm+(aq) + qXn−(aq).
How is the Ksp expression written for MpXq? | Ksp = [Mm+]^p [Xn−]^q.
Why are solids omitted from the Ksp expression? | Their activity is constant and defined as 1.
What is molar solubility? | The number of moles of a compound that dissolve per liter to form a saturated solution.
What variable is commonly used for molar solubility? | x.
For a 1:1 salt (e.g., AgCl), how are ion concentrations related to x? | [Ag+] = x and [Cl−] = x.
What is the Ksp–molar solubility relationship for a 1:1 salt? | Ksp = x².
For a 1:2 salt (e.g., CaF2), what are the ion concentrations? | [Ca2+] = x and [F−] = 2x.
What is the Ksp–molar solubility relationship for CaF2? | Ksp = 4x³.
For a 2:3 salt (e.g., Ca3(PO4)2), what are the ion concentrations? | [Ca2+] = 3x and [PO43−] = 2x.
What is the Ksp–molar solubility relationship for Ca3(PO4)2? | Ksp = 108x⁵.
What is Qsp? | The reaction quotient calculated using current ion concentrations.
How is Qsp used? | To predict whether precipitation will occur.
What does Qsp < Ksp indicate? | The solution is unsaturated; no precipitate forms.
What does Qsp = Ksp indicate? | The solution is saturated and at equilibrium.
What does Qsp > Ksp indicate? | The solution is supersaturated and precipitation will occur.
What happens when precipitation occurs? | Ions form a solid until Qsp equals Ksp.
What is the common ion effect? | Reduced solubility caused by the presence of a shared ion.
Why does a common ion reduce solubility? | It shifts equilibrium toward the solid.
Which principle explains the common ion effect? | Le Châtelier’s principle.
How does a common ion affect ICE tables? | The initial ion concentration is greater than zero.
What is selective precipitation? | Controlled removal of ions from a mixture by precipitation.
Which ion precipitates first in selective precipitation? | The ion that forms the least soluble compound.
What determines which compound precipitates first? | The one that reaches Qsp = Ksp first.
What is a practical application of selective precipitation? | Wastewater treatment to remove contaminants.
Why is selective precipitation useful analytically? | It allows separation of ions based on solubility differences.
What defines a Lewis acid? | A species that accepts an electron pair.
What defines a Lewis base? | A species that donates an electron pair.
How does the Lewis model differ from Brønsted–Lowry? | It focuses on electron pair transfer rather than proton transfer.
Who proposed the Lewis acid–base model and when? | G. N. Lewis in 1923.
What is a Lewis acid–base adduct? | The product formed when a Lewis acid and base combine.
What type of bond forms in a Lewis acid–base reaction? | A coordinate covalent bond.
What is a coordinate covalent bond? | A bond in which one atom provides both bonding electrons.
In coordination chemistry, what acts as the Lewis acid? | The central metal cation.
What acts as the Lewis base in a coordination complex? | The ligands.
What is a ligand? | A molecule or ion that donates an electron pair to a metal ion.
Give common examples of ligands. | H₂O, NH₃, CN⁻, OH⁻.
What is a complex ion? | A charged species consisting of a metal ion bonded to ligands.
What does the formation constant (Kf) measure? | The stability of a coordination complex.
Write the general meaning of a large Kf value. | The complex is very stable and strongly favored.
What does the dissociation constant (Kd) describe? | The tendency of a complex ion to break apart.
What is the relationship between Kf and Kd? | Kd = 1 / Kf.
Write the equilibrium expression for Kf. | Kf = [complex] / ([metal ion][ligand]^n).
Why does adding a ligand dissolve some precipitates? | Complex formation reduces free metal ion concentration.
Which principle explains ligand-induced dissolution of precipitates? | Le Châtelier’s principle.
Give an example of a precipitate dissolved by complex formation. | AgCl dissolves when NH₃ forms Ag(NH₃)₂⁺.
Why does complex formation shift solubility equilibria? | It removes metal ions from solution.
What are oxyanions? | Polyatomic ions formed from nonmetals bonded to oxygen.
How do Lewis acids participate in oxyanion formation? | Nonmetal oxides accept electron pairs from oxide ions.
Give an example of oxyanion formation. | SO₃ + O²⁻ → SO₄²⁻.
Is H⁺ a Lewis acid? | Yes, it accepts an electron pair.
Is NH₃ a Lewis base? | Yes, it donates an electron pair.
Why is BF₃ a Lewis acid? | It has an incomplete octet and accepts electron pairs.
Why is CN⁻ a strong Lewis base? | It has a lone pair and high electron density.
What role do Lewis acids play in coordination chemistry? | They accept electron pairs from ligands to form complexes.
What role do Lewis bases play in coordination chemistry? | They donate electron pairs to metal ions.
\What are coupled equilibria? | Two or more equilibrium reactions that share a reactant or product.
Why are coupled equilibria important? | They can dramatically shift equilibrium positions, often increasing solubility.
How does coupling affect a sparingly soluble solid? | Removing a product pulls dissolution forward, increasing solubility.
What type of equilibria often couples with solubility? | Acid–base equilibria and complex-ion formation.
What kind of anions increase solubility in acidic solutions? | Basic anions (CO₃²⁻, OH⁻, F⁻, PO₄³⁻).
Why does acidity increase solubility of carbonate salts? | H₃O⁺ consumes CO₃²⁻, removing a product of dissolution.
What principle explains solubility increase in acidic solution? | Le Châtelier’s principle.
Write the net reaction for CaCO₃ dissolution in acid. | CaCO₃(s) + H₃O⁺ ⇌ Ca²⁺ + HCO₃⁻ + H₂O.
Why is CaCO₃ more soluble in acidic conditions? | The net equilibrium constant is much larger than Ksp alone.
How does ocean acidification affect coral reefs? | Increased acidity dissolves CaCO₃ skeletons.
What causes tooth decay chemically? | Acids react with OH⁻ in hydroxyapatite, increasing enamel solubility.
How does fluoride protect teeth? | It replaces OH⁻ with the weaker base F⁻, reducing acid-driven dissolution.
What is solubility–complex-ion coupling? | Dissolution coupled with formation of a metal–ligand complex.
Why does complex formation increase solubility? | It removes free metal ions from solution.
What species is removed during complex-ion coupling? | The metal cation.
Give common ligands that increase solubility. | NH₃, OH⁻, CN⁻, S₂O₃²⁻.
How does Al(OH)₃ dissolve in strong base? | By forming Al(OH)₄⁻.
Write the complex formed when Al(OH)₃ dissolves in base. | Al(OH)₄⁻.
Why is Al(OH)₃ soluble in base but not water? | Strong complex formation shifts equilibrium strongly right.
How do equilibrium constants combine in coupled reactions? | They are multiplied.
What is the net equilibrium constant for complex-ion coupling? | K = Ksp × Kf.
What is the net equilibrium constant for acid–base coupling? | K = Ksp / Ka (when a basic anion reacts with acid).
Why is Knet often much larger than Ksp? | Additional reactions strongly favor product formation.
Which coupling increases solubility at low pH? | Acid–base coupling.
Which coupling increases solubility in ligand-rich solutions? | Complex-ion formation.
What ions benefit most from complex-ion coupling? | Metal cations (Ag⁺, Al³⁺, Cu²⁺).
What ions benefit most from acid–base coupling? | Basic anions (CO₃²⁻, PO₄³⁻, OH⁻).
What is the key conceptual takeaway of coupled equilibria? | Removing products drives dissolution far beyond Ksp alone.