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TITRIMETRY ANALYSIS - Coggle Diagram
TITRIMETRY ANALYSIS
Weak Acid-Strong Base Titration
Example: 50.0 mL of 0.10 M HCN titrated with 0.05 M NaOH
Reaction: HCN + NaOH -> NaCN + H2O
Ka of HCN = 4.9 x 10^-10
Evaluate titrant volumes
0 mL
25 mL
80 mL
100 mL
115 mL
140 mL
For each volume
Calculate moles of limiting reagent
Calculate moles of excess reagent
Identify compounds after reaction
Determine resulting solution and pH
Strong Acid-Strong Base Titration
Example: 50.0 mL of 0.10 M HCl titrated with 0.05 M NaOH
Reaction: HCl + NaOH -> NaCl + H2O
Evaluate titrant volumes
0 mL
25 mL
80 mL
100 mL
115 mL
140 mL
For each volume
Calculate moles of limiting reagent
Calculate moles of excess reagent
Identify compounds after reaction
Determine resulting solution and pH
Meaning of Titrimetry
Quantitative analytical technique
Uses a solution of accurately known concentration
Measures the volume required to react with the substance being determined
Acid-Base Theories
Arrhenius Theory
Acid: ionizes or dissociates in water to produce H+ or H3O+
Base: dissociates in water to produce OH-
Examples
HCl -> H+ + Cl-
NaOH -> Na+ + OH-
CH3COOH -> CH3COO- + H+
Bronsted-Lowry Theory
Acid: proton donor
Base: proton acceptor
An acid requires a base to accept its proton
Conjugate acid-base pairs
Acid1 and Base1 are conjugate pairs
Base2 and Acid2 are conjugate pairs
Lewis Theory
Acid: electron-pair acceptor
Base: electron-pair donor
Dissociation of Water and pH Scale
Water dissociation
H2O ⇌ H+ + OH-
H2O + H2O ⇌ H3O+ + OH-
Ionic product of water at 25 °C
Kw = [H+][OH-] = 1 x 10^-14
pH and pOH
pH = -log[H+]
pOH = -log[OH-]
pKa = -log Ka
pKb = -log Kb
pKw = -log Kw = 14 at 25 °C
pH + pOH = 14 at 25 °C
Ka x Kb = Kw
pH Determination of Acids and Bases
Strong acid and strong base
Completely dissociate
Use concentration of H+ or OH- to determine pH or pOH
Weak acid
Partially dissociates
Example: CH3COOH ⇌ H+ + CH3COO-
ICE table
Initial: acid concentration 0.2 M
Change: -x, +x, +x
Equilibrium: 0.2 - x, x, x
Weak base
Partially dissociates
Example: NH3 + H2O ⇌ NH4+ + OH-
ICE table
Initial: NH3 concentration 0.2 M
Change: -x, +x, +x
Equilibrium: 0.2 - x, x, x
Titration Calculations
Concentration of analytes
25.00 mL HCl, H2SO4 and H2C2O4 titrated separately with 0.10 M NaOH
NaOH volumes for complete reaction: 12.50 mL, 25.00 mL and 10.00 mL respectively
Calculate each analyte concentration using reaction stoichiometry
Equivalence point
Example: 100 mL of 0.10 M HCl titrated with 0.10 M NaOH
Determine pH at equivalence point
Weak acid and strong base mixture
Example: 10.0 mL of 0.10 M NaOH added to 50.0 mL of 0.10 M HCN
Ka of HCN = 4.9 x 10^-10
Calculate resulting pH
Main Applications
Determination of analyte concentration or type
Titrant: strong acid or strong base
Analyte: acid or base, strong or weak
Equivalence point: reactants have completely reacted
Determination of pH of resulting solution
Add titrant gradually
Identify limiting reagent
Identify excess reagent
Identify product
Determine type of solution after reaction
Types of Acids and Bases
Strong acid or base
Completely dissociate
Examples
HCl
Ba(OH)2
Weak acid or base
Partially dissociate
Examples
CH3COOH
NH3 + H2O -> NH4+ + OH-