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.