Acid base equilibria

Ka of strong acid

Very large

pKa of strong acid

very small

Salts that yield neutral solutions

both ions are conjugate to a strong acid or a strong base

• ions remain as ions in solution so pH is neutral

Solutions with one ion of weak properties

the weak species is the only active species and determines pH

• the ion is a conjugate of a weak acid or base

solutions with two ions with weak properties

pH is determined by the species with the largest equilibrium constant

• compare Ka and Kb

arrhenius acid base definition

Acids produce H+ in solution, bases produce OH- in solution

limitations of arrhenius definition

• only works in aqueous solutions

• only accepts bases with OH- ions

Bronsted-Lowry acid base definition

Acids are proton donors, bases are proton acceptors

• an acid-base reaction occurs when one species donates a proton and another simultaneously accepts i

conjugate acid-base pairs

species that differ by one proton

connection between bronsted-lowry and arrhenius definitions

all arrhenius bases are bronsted-lowry bases, but not all bronsted-lowry bases are arrhenius bases (don’t all contain OH-)

lewis acid base definition

acids are electron pair acceptors, bases are electron pair donors

• expands the definition of acids by bronsted-lowry to include substances other than H+

adduct

a hydrated cation formed when electron pairs in the O atoms of water form covalent bonds so the metal ion acts like a lewis acid

auto-ionization constant

Kw = 1.0e-14

• describes quantitatively how water dissociates very slightly into ions in an equilibrium process known as autoionization

purpose of pH scale

allows us to define acidic and basic solutions in terms of relative magnitudes of H3O and OH concentrations

strong acids and bases

the equilibrium concentration of H3O and OH is equal to the initial concentration of strong acid or base because they dissociate completely

net-direction of an acid-base reaction

proceeds to the greater extent in the direction in which a stronger acid and stronger base form a weaker acid and weaker base

strong acids

• HCl

• HBr

• HI

• HClO4

• HNO3

• H2SO4

strong bases

• LiOH

• NaOH

• KOH

• RbOH

• CsOH

• Mg(OH)2

• Ca(OH)2

• Sr(OH)2

• Ba(OH)2

Group 1 and 2 metals with OH (not Be)

properties of weak acids and bases

• small or intermediate K

• do not dissociate completely

• reaction usually proceeds towards reactants or equal reactants and products

organic acids

RCOOH or positively charged ammonium species

organic bases

Neutral species with amine group or RCOO-

calculating percent dissociation

amount dissociated divided by initial amount (H3O+/HA)

polyprotic acid

an acid that has several protons which can be donated

• as more protons are donated, they become weaker

buffers

a solution that contains appreciable amounts of both a weak acid (HA) and its conjugate base (A-)

• optimal buffers have equal amounts of each to give the greatest resistance to pH change

range of buffers being effective

plus/minus one pH unit

two ways to prepare buffers

• from conjugate pairs in a solution

• by partial neutralization

criteria for henderson-hasselbach equation

• [A-] and [HA] are greater than Ka x 100

• [A-]/[HA] is between 0.1 and 10 (must always check)

• both components of conjugate pairs are not dilute (more than 0.01M)

buffer capacity

the strength of the buffer to maintain a pH

• the amount of hydronium or hydroxide the buffer can neutralize before the pH change

max buffer capacity

when concentration of both conjugate species are equa