Acids/Bases

Properties of Acids

pp 186

Properties of Bases

• pp 186

Arrhenius Model of Acid/Base

• Acid• Produces H+/H3O+

(hydronium) when in solution

• HA + H2O H3O+ + A-

• HCl + H2O H3O+ + Cl-

• Base• Produces OH- when in

solution

• BOH B+ + OH-

• NaOH Na+ + OH-

Strong vs. Weak

• Strong Acid/Base dissociates 100%HA + H2O H3O+ + A-

No HA or BOH left over in solution• Weak acid or base only has less than 5% dissociation. Large amounts of

HA or BOH left in solution – will establish equilibrium

• Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

• Strong Bases: Group I metal hydroxides

• Anything else is considered weak.• Strength has no indication on power of the acid/base…only describes its

behavior in water

Brønsted-Lowery Model

• an acid is a H+ donor• HA + H2O H3O+ + A-

HNO3 + H2O H3O+ + NO3-

• When an acid donates a H+, a conjugate base is formed A- (is capable of accepting a H+).

• a base is a H+ acceptor• B + H2O BH+ + OH-

NH3 + H2O NH4+ + OH-

• Notice OH- is still produced but it is coming from the water

• When a base accepts a hydrogen ion, a conjugate acid is formed BH+ (is capable of donating a H+).

Identify Conjugate Acid Base Pairs

HClO2 (aq) + H2O (l) H3O+ (aq) + ClO2- (aq)

Acid Base CA CB

pp 187-186

Lewis Model

• Acid • Accepts a lone pair of

electrons from base

• Base• Donates a lone pair of

electrons to the acid

Auto Ionization of Water

• Water is an amphoteric substance, can act as both an acid and a base

• H2O + H2O H3O+ + OH-

• At 25°C [H3O+] = [OH-] = 1.0 x 10-7 M

Ion product constant for water Kw = 1.0 x 10-14

Kw = [H3O+] [OH-]

• pp 224

pH

• pH – the power of hydrogen • pH scale 0-14 – Value can be greater than 14 or less than 0

• pH = -log[H+]• If the [H+] > 1.0 x 10-7 (pH <7) acidic• If the [H+] < 1.0 x 10-7 (pH >7) basic• If the [H+] = 1.0 x 10-7 (pH =7) neutral

• [H+] = 10-pH

pOH• pOH – the power of hydroxide • pOH scale 0-14 • Value can be greater than 14 or less than 0• pH = -log[OH-]• If the [OH-] > 1.0 x 10-7 (pH <7) basic• If the [OH-] < 1.0 x 10-7 (pH >7) acidic• If the [OH-] = 1.0 x 10-7 (pH =7) neutral

• [OH-] = 10-pOH

• pH + pOH =14

Acid/Base Neutralization

Acid/Base Titration

• The general process of determining the molarity of an acid or a base through the use of an acid-base reaction is called an acid-base titration.

• The known reactant molarity is used to find the unknown molarity of the other solution.

• MVn =MVn

Tritration Curves

• Equivalence point mol H+ = mol OH- (inflection

point on curve)

• End point when the indicator changes color– Indicator is a substance that

is pH sensitive

• Want the equivalence point and end point to be the same

• Choose an indicator based on equivalence point

Strong Acid/Strong Base

• Equivalence pt occurs at about pH of 7.0

Weak Acid/Strong Base

• Equivalence pt >7 usually around 9

Strong Acid/Weak Base

• At equivalence pt pH<7 usually around 5

Common Indicators