Titrations Strong acid/strong Strong acid/weak Strong base/ Strong base/weak base base Strong acid acid Starting point high not as high low not as low Midpoint Not relevant pH= pKa Not relevant pH = pKa Equivalence point Exactly 7 Below 7 Exactly 7 Above 7 (conjugate acid (conjugate base present) present) Vertical region Very long Not as long Very long Not as long Always pick an indicator whose pKa = pH at the equivalence point of the titration. Various Ways to Describe Acid Strength Property Strong Acid Weak Acid Ka Too large to measure << 1 Position of the dissociation right left equilibrium Equilibrium concentration of [H+ ] = [HA]o [H+ ] << [HA]o H+ compared to the original concentration of HA Equilibrium concentration of [HA] ~ 0 M [HA] ~ [HA]o HA compared to the original [HA] << [HA]o concentration of HA Percent Dissociation 100% < 5% Strength of conjugate base Conjugate base is nonexistent Conjugate base is also weak, but inversely proportional in strength to the acid (Kb = Kw/Ka). How to represent in a net H+ + A- HA ionic equation Sign System Sign Sign of Sign of E0 K Spontaneous? Of H0 Entropy ofS0 G0 (if a (Thermodynamically Change favorable?) - + 1. Exothermic Increasing - + >1 always 2. Exothermic - Decreasing - + or - - or + Don’t know Low T + + + or - - or + 3. Endothermic Increasing Don’t know High T + - + - 4. Endothermic decreasing < 1 Galvanic Cell/ Spontaneous Chemical energy electrical energy E = + = - anode= Cathode = ΔG Voltaic Cell/ oxidation reduction Ex: battery! Electrochemical Cell
Titrations Strong acid/strong base Strong acid/weak base Strong base/ Strong acid Strong base/weak acid Starting point high not as high low not as low Midpoint Not relevant pH= pKa Not relevant pH = pKa Equivalence point Exactly 7 Below 7 (conjugate acid present) Exactly 7 Above 7 (conjugate base present) Vertical region Very long Not as long Very long Not as long Always pick an indicator whose pKa = pH at the equivalence point of the titration. Various Ways to Describe Acid Strength Property Strong Acid Weak Acid Ka Too large to measure << 1 Position of the dissociation equilibrium right left Equilibrium concentration of H+ compared to the original concentration of HA [H+ ] = [HA]o [H+ ] << [HA]o Equilibrium concentration of HA compared to the original concentration of HA [HA] ~ 0 M [HA] << [HA]o [HA] ~ [HA]o Percent Dissociation 100% < 5% Strength of conjugate base Conjugate base is nonexistent Conjugate base is also weak, but inversely proportional in strength to the acid (Kb = Kw/Ka). How to represent in a net ionic equation H+ + A- HA Sign Of H0 System Entropy Change Sign ofS0 Sign of G0 Sign of E0 (if a K Spontaneous? (Thermodynamically favorable?) 1. Exothermic - Increasing + - + >1 always 2. Exothermic - Decreasing - + or - - or + Don’t know Low T 3. Endothermic + Increasing + + or - - or + Don’t know High T 4. Endothermic + decreasing - + - < 1 Galvanic Cell/ Voltaic Cell/ Electrochemical Cell Spontaneous Ex: battery! Chemical energy electrical energy E = + ΔG = - anode= oxidation Cathode = reduction
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