Chapter 15 - Precipitation and Other Equilibria

If a compound is < 0.01 mol/L, it is generally considered:

insoluble

do you know the solubility rules?

yes/no

What is the solubility product constant?

Ksp

What is the equilibrium constant for the dissolution of a solid?

the solubility constant

What does Ksp tell you?

dissolves at equilibrium

Solubility =

amount that dissolves

Characteristics of the solubility equilibrium?

• slow, over & under values common

• mane chemical effects on equilibrium

• predictions of solubility from Ksp can be risky

What does a high vs. low Ksp value tell you?

a high Ksp means the compound is more soluble & a low Ksp means the compound is less soluble

Does Ksp have units?

no

If Ksp < Q, then the solution is:

supersaturated

If Ksp = Q, then the solution is:

saturated

If Ksp > Q, then the solution is:

undersaturated

What is the common ion effect?

the presence of an ion in common with that of an insoluble compound decreases the solubility

What conditions do lewis bases and acids work in?

in aqueous and non-aqueous conditions — not just water!

Lewis Base:

electron pair donor

Lewis Base:

electron pair donor

Many Brønsted - Lowry bases are also:

Lewis bases

For a base to accept a proton, it must contain:

an atom with a lone pair of electrons

Examples of Lewis bases are:

anions and neutral molecules with lone pairs (amines, water, etc.)

A proton (H +) can be both:

Brønsted - Lowry acid and a Lewis acid

However, most Lewis acids are not:

Brønsted - Lowry acids

Cations and electron deficient molecules are:

often Lewis acids

Is the cation positive?

yes

Is the anion negative?

yes

Brønsted Lowry acid/base reactions represent a subcategory of Lewis acid reactions, where:

the LA is H+

Complex ions are polyatomic ions that consist of a central atom, usually:

a transition metal surrounded by ions, or molecules called ligands

Ligands are:

Lewis bases

What is Kf?

formation constant — the equilibrium constant to form a complex

What is Kd?

dissociation constant — the inverse of the formation constant

What are two methods of dissolving compounds that are sparingly soluble (precipitates)?

• Add a strong acid to react with basic anions or ammonia in the compound

• Add a ligand (Lewis base) that reacts with the metal cation to form a complex ion

The solubility of many insoluble materials is a function of:

pH

Many sulfides & hydroxides, Pbs, Ag2S are soluble in:

acidic solutions

What is included and not included in Ksp expressions?

Included = gases & aqueous

Not Included = pure solids and liquids

What is molar solubility?

n_solute per liter of saturated solution (mol/L)

Solubility is the:

maximum possible concentration of a solute at a given temperature and pressure

What is another way to express solubility?

mass_solute per liter of saturated solution (g/L)

If Q > Ksp, precipitation occurs until:

Q = Ksp
- Q must decrease

What occurs at Q < Ksp?

no precipitation occurs

• Q could increase

• More solid could dissolve if present

What is the common ion effect based on?

Le Chatelier

Metal ions can act as Lewis Acids because they have:

• missing e-

• empty valence orbitals

• metal ion + lewis base —> complex ion

Hydroxide ions are Lewis bases because:

• O is e- rich (has large electronegativity)

• can easily donate an e- pair to a bond

What does amphoteric mean?

can act as both an acid and a base depending on the conditions

Many metal hydroxides are:

amphoteric

Lewis acids and bases typically produce:

adducts

What is an adduct?

two distinct molecules/atoms come together by simple addition

Lewis acid base reaction can also involve one base:

displacing another base

Many slightly soluble ionic compounds dissolve when the [metal ion] is:

concentration decreases by complex ion formation

Complex ion:

central metal ion bonded to one or more molecules or ions

Complex ion formation is highly:

favored