Chem Unit 4: Acids and Bases

Weak Bases

Bases that do not completely ionize.

Monoprotic Acids

Acids that have only one acidic proton.

Polyprotic Acids

Acids with more than one acidic proton.

Ka

Acid dissociation constant, a measure of acid strength.

Kb

Base dissociation constant, a measure of base strength.

pKa

The negative base-10 logarithm of the acid dissociation constant (Ka).

pKb

The negative base-10 logarithm of the base dissociation constant (Kb).

pH

The negative base-10 logarithm of the hydronium ion concentration [H3O+].

pOH

The negative base-10 logarithm of the hydroxide ion concentration [OH-].

Kw

The ion product constant for water.

pKw

Equals pKa + pKb = 14.

Oxyacids

Oxygen containing acid.

pH

A measure of the concentration of hydrogen ions in a solution; calculated as the negative logarithm of [H+].

pH Formula

pH = -log[H+]

pOH

A measure of the concentration of hydroxide ions in a solution; calculated as the negative logarithm of [OH-].

pOH Formula

pOH = -log[OH-]

pH and pOH Relationship

pH + pOH = 14

Strong Acid

An acid that completely dissociates into ions in solution.

Strong Base

A base that completely dissociates into ions in solution.

Weak Acid

An acid that only partially dissociates into ions in solution.

Ka

The equilibrium constant for the dissociation of a weak acid.

Kb

The equilibrium constant for the dissociation of a weak base.

Relationship Between Ka, Kb, and Kw

Kw = Ka * Kb

Approximation Method

Used to simplify calculations for weak acids and bases, assuming that the change in initial concentration is small.

Validity of Approximation Rule

If the initial concentration of the acid or base is 1000 times greater than Ka or Kb, the approximation is valid.

5% Rule

If the change in concentration is less than 5% of the initial concentration, the approximation is valid.

Polyprotic Acid

An acid with multiple ionizable protons.

Oxalic Acid

A polyprotic acid with two ionization constants, Ka1 and Ka2.

Common Ion Effect

The shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substance.

Buffer

A solution that resists changes in pH upon the addition of small amounts of acid or base.

pH Buffer

Resists change to added H+ or OH-.

Henderson-Hasselbalch Equation

pH = pKa + log ([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid.

pKa

pKa = -log(Ka), where Ka is the acid dissociation constant.

Aqueous Equilibria

Deals with buffers, titrations, and solubility (Ksp).

Buffer Solutions

Solutions that resist changes in pH upon addition of small amounts of acid or base.

Titration

An analytical technique used to determine the concentration of an unknown solution by neutralizing it with a solution of known concentration (titrant).

Analyte

The substance being analyzed in a titration.

Endpoint

The point at which the titration has ended, ideally coinciding with the equivalence point.

Equivalence Point (Eq. Pt.)

The point in a titration where the amount of titrant added is chemically equivalent to the amount of analyte in the sample.

Acid/Base Titration

A type of titration involving reactions between acids and bases.

Titrations of Polyprotic Acids

Titration involving acids that can donate more than one proton.

Solubility Product (Ksp)

The equilibrium constant representing the solubility of a sparingly soluble salt.

Solubility Product (Ksp)

The equilibrium constant for the dissolution of a solid substance into an aqueous solution.

LD50

The amount of a chemical that is lethal to 50% of the experimental animals exposed.

Common Ion Effect

The decrease in solubility of an ionic precipitate by the addition of a different ionic compound that contains the same ion as found in the ionic precipitate; a consequence of Le Chatelier's Principle.

Barium Sulfate (BaSO4)

An insoluble compound of barium; used as an absorber and shows white on X-rays to help in GI tract investigations.

Molar Solubility (s)

The solubility of a compound expressed in moles per liter (mol/L).