Acids/Bases
Jan 21, 2016
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