Chapter 15: Equilibria of other Reaction Classes

Solubility Product Constant (Ksp)

Equilibrium constant for the dissolution of a slightly soluble ionic compound (saturated)

• “Slightly” so it can be reversible for a K

• Nothing is completely insoluble, just very little dissolves

• At EQUILIBRIUM only

Solubility Product Constant (Ksp) Eqn

Ksp = [M^y+]^x [N^x-]^y

T/F: Change in temperature will change Ksp.

True; increasing temp will increase solubility which would give a higher Ksp.

Molar Solubility (S)

Solubility of a compound expressed in units of moles per liter (mol/L)

Related with Ksp

Precipitation rxns

Occur upon the mixing of 2 solutions when one of the cross products is insoluble

Reaction Quotient (Q)

For rxn by which an ionic compound dissolves is the product of the concs of the ionic components raised to their stoichiometric coefficients

• Under ANY conditions

Reaction quotient Q < Ksp

• Unsaturated

• More solid dissolves

• No precipitation

Q = Ksp

• Saturated

• Additional solid does not dissolve

• Precipitate forms

Q > Ksp

• Supersaturated

• Excess solid precipitates out

• Precipitate forms

Common Ion Effect on Solubility

Effect on equilibrium when a substance w/ a common ion with the dissolved ionic species is ADDED to the solution, which decreases the solubility of an ionic species

Solubility of an ionic compound is (higher/lower) in a solution containing a common ion than that in pure water.

Lower

T/F: For an ionic compound with a basic anion, the lower the pH, the higher the solubility.

True

Common basic anions: OH-, S^2-, and F-

Solubility in basic solution

Equilibrium shifts LEFT ← due to common ion effect = lower solubility

Solubility in acidic solution

Equilibrium shifts RIGHT → due to neutralization of H3O+ and OH- = higher solubility

Selective precipitation

Process where ions are separated using diffs in solubility w/ given precipitating reagent

• Ion reqs that the smallest amt of added ion precipitates first

T/F: The salt that forms at the lower ion precipitates first, so compare the 2.

True

Arrhenius Acid

Produces H+

Arrhenius Base

Produces OH-

Bronsted-Lowry Acid

Donates H+

Bronsted-Lowry Base

Accepts H+

Lewis Acid

Accept pair of electrons (e-)

Lewis Base

Donate pair of electrons (e-)

Lewis Acids and Empty Orbital Types

Lewis acids have an empty orbital that can accept an electron pair (cannot include H)

1. Incomplete octet = BF3, AlCl3, BCl3, and BeH2

2. Molecules that contain double bonds = rearrange electrons to accept a pair of electrons

3. Small and highly charged cations = Al^3-, Ag+, Fe^3+, Cr^3+, and Zn^2+