1 TITRATION CURVES K (A) + (R) (P) (A) + (R) (P) analyte titrant product Titration curves: 1. Strong acidstrong base,Strong base strong acid 1. Strong acid withstrong base, Strong base with strong acid 2.Weak acidstrong base,Weak basestrong acid 2. Weak acid withstrong base, Weak basewith strong acid 3.Polyprotic acid strong base 3. Polyprotic acid withstrong base Important points and regions : before titrationI.[A] 2 points:before titration (at 0%)I.[A] at the end pointIII.[A] = [R] at the end point (at 100 %)III.[A] = [R] before the end pointII.[A] + [P] 2 regions:before the end point ( – 99.99…%)II.[A] + [P] after the end pointIV.[P] + [R] after the end point( – ∞)IV.[P] + [R] NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detection Applications Outline NEUTRALIZATION ANALYSIS

2 TITRATION CURVES I.At the start: HCl + NaOH Cl – +Na + (H 2 O) acid 1 + base 2 base 1 + acid 2 (very weak) (very weak) e.g. 1. Strong acidstrong base,Strong base strong acid 1. Strong acid with strong base, Strong base with strong acid II.Before the end point: [H + ] = [H 3 O + ]=[HCl] unreacted [OH – ] = [NaOH] unreacted pH = – lg [HCl] unreacted pOH = – lg [NaOH] unreacted III.At the end point: [H + ]≡ [OH – ] K W = 10 –14 pH≡ 7 IV.After the end point: [OH – ] = [NaOH] excess [H + ] = [H 3 O + ]=[HCl] excess pOH = – lg [NaOH] excess pH = – lg [HCl] excess Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detection Applications [H + ] = [H 3 O + ]=[HCl] 0 [OH – ] = [NaOH] 0 pH = – lg [HCl] 0 pOH = – lg [NaOH] 0 pH = 14 – pOH

3 TITRATION CURVES 1. Effect of the temperature: 100°C[H + ]·[OH – ] = K w = 10 –12 Neutr. point: pH = 6 100°C [H + ]·[OH – ] = K w = 10 –12 Neutr. point: pH = 6 25°C[H + ]·[OH – ] = K w = 10 –14 Neutr. point: pH = 7 25°C [H + ]·[OH – ] = K w = 10 –14 Neutr. point: pH = 7 Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detection Applications Titration curves: 1. Strong acidstrong base,Strong base strong acid 1. Strong acid withstrong base, Strong base with strong acid 2.Weak acidstrong base,Weak basestrong acid 2. Weak acid withstrong base, Weak basewith strong acid 3.Polyprotic acid strong base 3. Polyprotic acid withstrong base EFFECTS ON THE TITRATION CURVE:

4 EFFECTS ON THE TITRATION CURVE 2. Dependence on the initial concentrations (e.g. [HCl]): [HCl] 0 ↓ 0%50%90%99%99.9%100%100.1%101%110% 1 N 0 0, ,1 N11, ,01 N22, ,001 N33, ΔpH 3 – 11 4 – 10 5 – 9 6 – 8 pH change around the end point NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detection Applications Outline

5 3. Dependence on the acid strength (dissociation constants): A. Weak acidstrong bases A. Weak acid with strong bases, EFFECTS ON THE TITRATION CURVE NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detection Applications Outline CH 3 COOHNaOH e.g. 10 –1 N CH 3 COOH is titrated with NaOH (K a = 2x10 –5 )% pH ΔpH 9 PHENOLPHTALEIN pK Ind ≈ 9 → PHENOLPHTALEIN B. Weak base strong acid B. Weak base with strong acid% pH ΔpH 5 METHYL RED pK Ind ≈ 5 → METHYL RED NH 4 OH HCl e.g. 10 –1 N NH 4 OH is titrated with HCl (K b = 2x10 –5 )

6 TITRATION CURVES I. At the start: I. At the start: pH II. Weak acidstrong base Weak base strong acid II. Weak acid with strong base Weak base with strong acid Weak acid Weak base II. Before the end point: pH Buffer (acid / salt) Buffer (base / salt) III. At the end point: pH Hydrolysing salt (Brönsted base) Hydrolysing salt (Brönsted acid) IV. After the end point: pH Excess of strong base [OH – ] = C excess base [OH – ] = [NaOH] excess [H + ] = C excess acid [H + ] = [HCl excess Excess of strong acid Introduction Titrants Titration curves End point detection Applications Outline NEUTRALIZATIONANALYSIS CH 3 COOHNaOH Titration ofNH 4 OH HCl: e.g. Titration of CH 3 COOH with NaOH, Titration of NH 4 OH with HCl:

7 TITRATION CURVES III. Polyprotic acidstrong base III. Polyprotic acid with strong base 1.H 3 PO 4 + OH – H 2 PO 4 – + H 2 O 1.H 3 PO 4 + OH – H 2 PO 4 – + H 2 OK a1 = 7x10 –3 2.H 2 PO 4 – +OH – HPO 4 2– +H 2 O 2.H 2 PO 4 – + OH – HPO 4 2– + H 2 OK a2 = 6x10 –8 3.HPO 4 2– + OH – PO 4 3– + H 2 O 3.HPO 4 2– + OH – PO 4 3– + H 2 OK a3 = 10 –12 H 3 PO 4 NaOH e.g. Titration of H 3 PO 4 with NaOH Introduction Titrants Titration curves End point detection Applications Outline NEUTRALIZATIONANALYSIS

8 ACID / BASE INDICATORS 1.Azo-compounds Genearal structure: Mechanism: Yellow Yellow (basic) (aromatic) Yellow Yellow (intermediate) (protonated) Red Red (acidic) (quinoid) NEUTRALIZATIONANALYSIS Outline Introduction Titrants Titration curves End p. detection - chemical - instrumental Applications

9 ACID / BASE INDICATORS ACID / BASE INDICATORS 2.PHTHALEIN-derivatives General structure: Mechanism: Colorless Colorless (acidic) Colorless Colorless (intermediate) Purple (basic) Thymol blue NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End p. detection - chemical - instrumental Applications Outline

10 INSTRUMENTAL DETECTION Method Sensing device Type of titration POTENTIOMETRY (Potential %) (Potential vs %) Different types of electrodes electrodes Neutralization titr. Complexometric titr. Precipitation titr. Redox titr. sensing devices. The titration process is followed by electrochemical, photometric or other sensing devices. (Summary)AMPEROMETRY (Current %) (Current vs %) Pt Pt electrode (dead stop…) Redox titr. CONDUCTOMETRY (Conductivity %) (Conductivity vs %) Conductivity cell Neutralization titr. Precipitation titr. PHOTOMETRY (A = ε · c · l %) (A = ε · c · l vs %)Spectrophotometer Complexometric titr. ENTALPHYMETRY (Q = f (c, ΔH) % (Q = f (c, ΔH) vs %Thermistor Neutralization titr. Complexometric titr. Precipitation titr. Redox titr. Outline INSTRUMENTALDETECTION AdvantagesTypes Potentiometric end point detection Conductometric end point detection

11POTENTIOMETRY Nernst equation: Electrode potential developed between: Neutralization titration: Complexometric titration: E = E 0 + lg [M n+ ] Indicator electrode Reference electrode Glass electrode Metalelectrode Precipitation titration: Redox titration: E = E lg [X − ] E = E 0 + lg [ox] [red] Ion-selectiveelectrode Nobel metal electrode Common reference electrodes: Solid metal / its „unsoluble” salt / saturated conc. of anion e.g. Ag / AgCl / KCl Hg / Hg 2 Cl 2 / KCl Hg / Hg 2 SO 4 / K 2 SO 4 E = E lg [H + ] n n constant potential  Known, constant potential (E ref ) Independent  Independent of theconcentration of the analyte concentration Potential  Potential (E ind ) varies Depends on  Depends on concentration the analyte concentration Outline INSTRUMENTALDETECTION Advantages Types Potentiometric end point detection Conductometric end point detection

12 POTENTIOMETRY Neutralization analysis Indicator electrode: GLASS ELECTRODE Electrochemical cell for measurement of pH: Internal reference electrode (Ag/AgCl/KCl) Internal| Internal| buffer sol. | buffer sol. | | (KCl) (pH = 7)| pH-sensitive| glass- | glass- | membrane | membrane | H + conc. | to be | to be | determined | External reference|| electrode || electrode || || (Hg/Hg 2 Cl 2 /KCl)|| ███████████ External Dry glass Internal hydrated gel layer External External reference electrode Glass electrode H + conc. to be determined Outline INSTRUMENTALDETECTION Advantages Types Potentiometric end point detection Conductometric end point detection

13 POTENTIOMETRY Glass electrode Composition of glass: E.g. 22 % Na 2 O, 6 % CaO, 72 % SiO 2. Ion-exchange reaction: between H + in the solution H + in the solution and Na + in the glass Na + in the glass: Combination glass electrode: Na + mobile K K H + + Na + Gl −  Na + + H + Gl – K = LARGE! solution glass solution glass Na + H+H+ solution membran e Na + H+H+ H+H+ Outline INSTRUMENTALDETECTION Advantages Types Potentiometric end point detection Conductometric end point detection

14 POTENTIOMETRY Titration curve Potentiometric titration curve: potential (pH) ofvolume Measuring the potential of a suitable indicator electrode (pH) as a function of volume titrant. Determination of the end point: derivatives Determination of the end point: from the derivatives 1 st derivative 2 nd derivative Titration curve Outline INSTRUMENTALDETECTION Advantages Types Potentiometric end point detection Conductometric end point detection

15 CONDUCTOMETRIC TITRATION CURVES I. Titration of strong acid (a) strong basee.g. HCl NaOH I. Titration of strong acid (a) with strong basee.g. HCl with NaOH (b) weak basee.g. HCl NH 4 OH (b) with weak basee.g. HCl with NH 4 OH II. Titration of weak acid(c) strong basee.g. CH 3 COOH NaOH II. Titration of weak acid(c) with strong base e.g. CH 3 COOH with NaOH (d) weak basee.g. CH 3 COOH NH 4 OH (d) with weak basee.g. CH 3 COOH with NH 4 OH % % Outline INSTRUMENTALDETECTION Advantages Types Potentiometric end point detection Conductometric end point detection

16APPLICATIONS I. Determination of strong acids / bases: Equivalence point:pH = 7 Equivalence point: pH = 7 TITRATIONS Direct Direct Back (indirect): Back (indirect): Analyte Titrant in excess to measure to calculate Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detectionApplications NaOH e.g. NaOH V phen. V meth.r. OH −  H 2 O

17 APPLICATIONS carboxylic acids of low carbon atoms e.g.  carboxylic acids of low carbon atoms e.g. CH 3 COOH II. (a) Determination of weak acids : CO 2 (as carbonate or hydrogencarbonate) e.g.  CO 2 (as carbonate or hydrogencarbonate) Application of CO 2 determination: Determination of organic materials Determination of organic materials Determination of CO 2, HCO 3 –, CO 3 2– Determination of CO 2, HCO 3 –, CO 3 2– content of natural waters Distillation apparatus (Maros- Schulek) (Maros- Schulek) Nonaqueous solvents: K a < 10 –7 Nonaqueous solvents: K a < 10 –7 > 10 –12 fatty acids  fatty acids (e.g. fat, wax, oil) Direct: Direct: Back :if the weak acid is volatile Back :if the weak acid is volatile II.Determination of weak acids : weak bases : Equivalence point:pH > 7 (phenolphtalein indicator) Equivalence point: pH > 7 (phenolphtalein indicator) Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detectionApplications Equivalence point:pH < 7 (methyl red indicator) Equivalence point: pH < 7 (methyl red indicator) K a ≥ 10 –5. (10 – –4 ) bubble-free bubble-free distillation distillation CO 2 Ba(OH) 2 CO 2 known amount of Ba(OH) 2  back titrationexcessBa(OH) 2 back titration of excess Ba(OH) 2 with HCl with standard HCl

18 APPLICATIONS Direct: NH 4 OH Direct:  e.g. NH 4 OH Back: NH 4 + -saltNH 3 Back:  NH 4 + -saltNH 3 Application of NH 3 determination: N-containing organic compounds (e.g. amino acids, proteins,…) N-containing organic compounds (e.g. amino acids, proteins,…) strong base (NaOH) boiling Kjeldahl method: Decomposition (mineralization) with cc. H 2 SO 4, 300 °C + catalyst: Se, or Cu 2+ + catalyst: Se, or Cu 2+ Ox. number: – 3  (NH 4 ) 2 SO 4 (e.g.. – NH 2, –N(CH 3 ) 2, =NH, –N<) Ox. number: + 3, +1  HNO 3 (+5) (e.g.,azo- (-N=N-), nitro-, nitrozo comp.) Reduction with Zn, Na 2 S 2 O 4,.. Nonaqueous solvents: K b < 10 –7 Nonaqueous solvents: K b < 10 –7 > 10 –12 NH 4 + distillation into known excess of acid Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detectionApplications II. (b) Determination of weak bases : K b ≥ 10 –5 (10 – –4 ) NH 3 known HCl  back titration of excess acid (HCl) with basic titrant (NaOH)

19APPLICATIONS NOT MEASURABLE! III. Determination of salts: Aniline · HCl; Benzidine ·H 2 SO 4 ; Papaverine · HCl… E.g. Aniline · HCl; Benzidine ·H 2 SO 4 ; Papaverine · HCl… (a)Neutral salts: (b)Salt hydrolyzing to acid: (b)Salt hydrolyzing to acid:Brönsted acid (strong acid + weak base) H + MA+H 2 O  MOH+A – + H + if pK > 7! can be TITRATED with base with base (c)Salt hydrolyzing to base:Brönsted base (c)Salt hydrolyzing to base:Brönsted base (strong base + weak acid) OH – MA+H 2 O  HA+M + + OH – if pK > 7 can be TITRATED with acid E.g. Na 2 B 4 O 7 methyl red (B 4 O 7 2– +7H 2 O  4H 3 BO 3 + 2OH – ) methyl red Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detectionApplications Na 2 CO 3 E.g. Na 2 CO 3 phenolpht. (CO 3 2– +H 2 O  HCO 3 – +OH – ) phenolpht. methyl red (CO 3 2– +2H 2 O  H 2 CO 3 +2OH – ) methyl red NaHCO 3 NaHCO 3 methyl red (HCO 3 – +H 2 O  H 2 O + CO 2 +OH – ) methyl red NaHCO 3 NaHCO 3 V meth.r. HCO 3 −  H 2 CO 3 V phen = 0 CO 3 2−  HCO 3 −  H 2 CO 3 Na 2 CO 3 V phen V meth.r.

20 (d)Specific determinations: NaOH – Na 2 CO 3 in the presence of each other Outline NEUTRALIZATIONANALYSIS Introduction Titrants Titration curves End point detectionApplicationsAPPLICATIONS OH −, CO 3 2−  HCO 3 −  H 2 CO 3 OH −, CO 3 2−  HCO 3 −  H 2 CO 3 A.OH – +H +  H 2 O Warder’s method :. CO 3 2– +H +  HCO 3 –. methyl red B.HCO 3 – +H +  H 2 CO 3 methyl red one sample : two samples : B.OH − +H +  H 2 O CO 3 2– +2H +  H 2 CO 3 methyl red phenolpht. Winkler’s method : A.+ BaCl 2 CO 3 2– +Ba 2+  BaCO 3 OH – +H +  H 2 Ophenolpht. V phen V meth.r. NaHCO 3 – Na 2 CO 3 in the presence of each other Warder’s method : two samples :. A.CO 3 2– +H +  HCO 3 – phenolpht.. B.HCO 3 – +H +  H 2 CO 3 CO 3 2− +2H +  H 2 CO 3 methyl red CO 3 2−  HCO 3 − HCO 3 −  H 2 CO 3 V phen V meth.r.