Acids and bases

Arrhenius definition of acids

Produce H+ ions when dissolved in water to form aqueous solutions

Modified Arrhenius definition of acids

Produce hydronium ions when dissolved in water to form aqueous solutions

Arrhenius definition of bases

Produce hydroxide ions when dissolved in water to form aqueous solutions

Bronsted-Lowry definition of acids and bases

An acid is a substance that donates H+. A base is a substance that accepts H+.

Conjugate acid

Product that accepted the H+ ion

Conjugate base

Product that lost an H+ ion

Amphoteric/amphiprotic

Substances that can act as both acids and bases

Conjugate acid-base pair 1

HA, A-

Conjugate acid-base pair 2

B, BH+

Strong acids

HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3

Strong bases

LiOH, NaOH, KOH, RbOH, CsOH, CaOH, Sr(OH)2, Ba(OH)2

Diprotic acids

Have two H+ ions which dissociate one at a time

Weak bases are

Weak electrolytes

Self-ionization of water

The equilibrium reached between the conjugate acid-base pairs of water produces both H₃O⁺ and OH^-.

Because pH is a log scale, a change of one pH unit corresponds to

a tenfold change in [H3O+].

Percent ionization

([H^+]equilibrium / [HA]initial) * 100

Polyprotic acids

have more than 1 ionizable H⁺. It is easier to remove the first hydrogen, the K_a values become smaller for each hydrogen that is removed

Types of weak bases

1. Neutral substance with a nonbonding electron pair to act as a proton acceptor

   1. The anions(conjugate base) of weak acids

K_a*K_b =

K_w = 1×10^-14 (only works for conjugate acid-base pairs)

pK_a+pK_b =

pK_w = 14.00 @ 25^oC

Hydrolisis

when a substance reacts with water to form H⁺ or OH^-

An anion (X^-) can be considered

the conjugate base of an acid

If the acid is strong, then the conjugate base

will have no effect on the pH of the solution

If the acid is weak, then the conjugate base

is a weak base and will form hydroxide ions which increase the pH making it basic

A cation that is a conjugate acid of a weak base

will decrease pH

A cation that is part of a strong base

will not affect pH

When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base,

the ion with the largest K influences pH

The common-ion effect

whenever a weak electrolyte and a strong electrolyte containing a common ion are together in solution, the weak electrolyte ionizes less that it would if it were alone in the solution

A buffered solution or buffer

contains a weak conjugate acid-base pair, will resist a change in pH if an acid or base is added

Henderson-Hasselbalch equation (calculating the pH of a buffer)

pH = pK_a + log ([A^- (conjugate base)] / [HA (acid)])

An ideal buffer

contains equal concentrations of the weak acid and conjugate base, pH = pK_a

Buffer capacity

the amount of acid or base that the buffer can neutralize before the pH begins to change drastically

2 steps to calculations involving the addition of a strong acid or base:

1. Stoichiometry of the neutralization

   1. Equilibrium calculation using Henderson-Hasselbalch equation

Acid-base titrations have 2 important points:

1. Equivalence point - the point at which stoichiometrically equivalent amounts of acid and base have been added

2. End point - the point at which the indicator changes color

There are 4 important points in a strong acid-strong base titration curve:

1. Initial pH - the pH of the initial solution is determined by the [H⁺]

2. Between the initial pH and the equivalence point - pH determined by the amount of acid not yet neutralized

3. Equivalence point - pH is 7.00

4. After the equivalence point - pH determined by amount of excess base

There are 4 important points on a weak acid-strong base titration curve:

1. Initial pH - calculated using the K_a of the weak acid

2. Between the initial pH and the equivalence point - pH is calculated based on the neutralized acid (buffer)

3. Equivalence point - pH is calculated based on the neutralization of the acid, will be >7

4. After the equivalence point - pH is calculated based on the excess base

The pH at the equivalence point is

above 7.00 for a weak acid and equals 7.00 for a strong acid

The titration curve for a polyprotic acid has

an equivalence point for each hydrogen removed

Oxoacids, or oxyacids,

contain an atom bonded to one or more oxygen atoms, sometimes with hydrogen atoms attached

Inductive effect

the attraction of electrons in adjacent bonds by more electronegative atoms

Weak acids do not experience

a strong induced dipole force

Less polarity in a molecule results in

the hydrogen ion being more attracted to the oxygen and thereby less ionizable

The conjugate bases are less stable,

which results in a stronger base