Chem: Ch 14 Acids and Bases

Arrhenius concept

a concept postulating that acids produce hydrogen ions in aqueous solution, while bases produce hydroxide ions.

Brønsted–Lowry model

a model proposing that an acid is a proton donor, and a base is a proton acceptor.

conjugate base

what remains of an acid molecule after a proton is lost.

conjugate acid

the species formed when a proton is added to a base.

conjugate acid–base pair

two species related to each other by the donating and accepting of a single proton.

acid dissociation constant

Ka the equilibrium constant for a reaction in which a proton is removed from an acid by to form the conjugate base and H3O+.
(for the reaction in which a proton is removed from HA to form the conjugate base A-)

strength of an acid

defined by the equilibrium position of its dissociation (ionization) reaction

strong acid

this equilibrium lies far to the right. This means that almost all the original HA is dissociated (ionized) at equilibrium
(A strong acid yields a weak conjugate base—one that has a low affinity for a proton. A strong acid also can be described as an acid whose conjugate base is a much weaker base than water (Fig. 14.5). In this case the water molecules win the competition for the H+ ions.)
LARGE Ka

weak acid

The equilibrium lies far to the left. Most of the acid originally placed in the solution is still present as HA at equilibrium. That is, a weak acid dissociates only to a very small extent in aqueous solution
(a weak acid has a conjugate base that is a much stronger base than water. In this case a water molecule is not very successful in pulling an H+ ion from the conjugate base. The weaker the acid, the stronger its conjugate base.)
SMALL Ka

diprotic acid

an acid having two acidic protons

oxyacids

an acid in which the acidic proton is attached to an oxygen atom.

Organic acids

an acid with a carbon-atom backbone; often contains the carboxyl group.

monoprotic acids

an acid with one acidic proton.

autoionization

the transfer of a proton from one molecule to another of the same substance.

ion-product constant (or the dissociation constant

the equilibrium constant for the auto-ionization of water;
Kw= [OH][H+]
1.0 × 10^-14

pH scale

a convenient way to represent solution acidity
-log[H+]

major species

the components present in relatively large amounts in a solution.

percent dissociation

the ratio of the amount of a substance that is dissociated at equilibrium to the initial concentration of the substance in a solution, multiplied by .

Many types of proton acceptors (bases) do not contain the hydroxide ion. However, when dissolved in water, these substances increase the concentration of hydroxide ion because of their reaction with water.

these reactions have a Kb=
always refers to the reaction of a base with water to form the conjugate acid and the hydroxide ion.

polyprotic acids

an acid with more than one acidic proton. It dissociates in a stepwise manner, one proton at a time.
(always dissociates in a stepwise manner, one proton at a time.)
- has a Ka1 and Ka2

Phosphoric acid

typical of most polyprotic acids in that the successive Ka values are very different.
only the first dissociation step makes an important contribution to H+ .
not a rate determining step

Sulfuric acid

unique among the common acids in that it is a strong acid in its first dissociation step and a weak acid in its second step:

Salt

an ionic compound

Salts That Produce Neutral Solutions

Recall that the conjugate base of a strong acid has virtually no affinity for protons in water. This is why strong acids completely dissociate in aqueous solution.
Salts that consist of the cations of strong bases and the anions of strong acids have no effect on [H] when dissolved in water.

Kw=

Ka x Kb

For any salt whose cation has neutral properties (such as Na1 or K1) and whose anion is the conjugate base of a weak acid,

the aqueous solution will be basic.

Base Strength in Aqueous Solutions

Salts That Produce Acidic Solutions

In general, salts in which the anion is not a base and the cation is the conjugate acid of a weak base produce acidic solutions.

A second type of salt that produces an acidic solution is one that contains a highly charged metal ion.

The Effect of Structure on Acid–Base Properties

Lewis acid

an electron-pair acceptor.

Lewis base

an electron-pair donor.

Brønsted–Lowry acid–base reactions

proton donor–proton acceptor reactions