1. Potentiometric Titration
Week 3

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

7. TITRATION CURVES Outline
1. Strong acid with strong base, Strong base with strong acid
Outline
NEUTRALIZATION
ANALYSIS
HCl + NaOH Cl– + Na+(H2O)
acid base2 base1 + acid2
(very weak)
e.g.
Introduction
Titrants
Titration curves
End point detection
Applications
At the start:
[H+] = [H3O+]=[HCl]0 [OH–] = [NaOH]0
pH = – lg [HCl]0 pOH = – lg [NaOH]0 pH = 14 – pOH
Before the end point:
[H+] = [H3O+]=[HCl]unreacted [OH–] = [NaOH]unreacted
pH = – lg [HCl]unreacted pOH = – lg [NaOH]unreacted
At the end point:
[H+] ≡ [OH–]
KW = 10–14 pH ≡ 7
After the end point:
[OH–] = [NaOH]excess [H+] = [H3O+]=[HCl]excess
pOH = – lg [NaOH]excess pH = – lg [HCl]excess

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

9. 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
0,3 1 2 3 7 11 12 13
0,1 N
1,3 4 10
0,01 N
2,3 5 9
0,001 N
3,3 6 8
Outline
pH change around the end point
NEUTRALIZATION
ANALYSIS
ΔpH
3 – 11
4 – 10
5 – 9
6 – 8
Introduction
Titrants
Titration curves
End point detection
Applications
100

10. EFFECTS ON THE TITRATION CURVE
3. Dependence on the acid strength (dissociation constants):
A. Weak acid with strong bases ,
Outline
100
e.g. 10–1 N CH3COOH is titrated with NaOH (Ka = 2x10–5)
NEUTRALIZATION
ANALYSIS % 50 90 99
99.9
100
100.1
101
110 pH
2.9
4.7
5.7
6.7
7.7
8.9 10 11 12
Introduction
Titrants
Titration curves
End point detection
Applications
ΔpH
pKInd ≈ 9 → PHENOLPHTALEIN
B. Weak base with strong acid
e.g. 10–1 N NH4OH is titrated with HCl (Kb = 2x10–5) % 50 90 99
99.9
100
100.1
101
110 pH
11.1
9.3
8.3
7.3
6.3
5.1 4 3 2
ΔpH
pKInd ≈ 5 → METHYL RED

11. TITRATION CURVES Outline
II. Weak acid with strong base Weak base with strong acid
e.g. Titration of CH3COOH with NaOH , Titration of NH4OH with HCl:
I. At the start: pH
Weak acid
Weak base
II. Before the end point: pH
Buffer (acid / salt)
Buffer (base / salt)
Outline
NEUTRALIZATION
ANALYSIS
III. At the end point: pH
Introduction
Titrants
Titration curves
End point detection
Applications
Hydrolysing salt (Brönsted base)
Hydrolysing salt (Brönsted acid)
IV. After the end point: pH
Excess of strong base
Excess of strong acid
[OH–] = Cexcess base
[H+] = Cexcess acid
[OH–] = [NaOH]excess
[H+] = [HClexcess

12. Outline TITRATION CURVES III. Polyprotic acid with strong base
e.g. Titration of H3PO4 with NaOH
H3PO4 + OH– H2PO4– + H2O Ka1 = 7x10–3
H2PO4– + OH– HPO42– + H2O Ka2 = 6x10–8
3. HPO42– + OH– PO43– H2O Ka3 = 10–12
Outline
NEUTRALIZATION
ANALYSIS
Introduction
Titrants
Titration curves
End point detection
Applications

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

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

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

16. Electrode potential developed
POTENTIOMETRY
Electrode potential developed
between:
Indicator electrode
Reference electrode
Potential (Eind) varies
Depends on
the analyte concentration
Known, constant potential (Eref)
Independent
of the analyte concentration
Outline
Common reference electrodes:
Solid metal / its „unsoluble” salt / saturated conc. of anion
INSTRUMENTAL
DETECTION
e.g. Ag / AgCl / KCl
Hg / Hg2Cl2 / KCl
Hg / Hg2SO4 / K2SO4
Advantages
Types
Potentiometric end point detection
Conductometric end point detection
Nernst equation:
Glass electrode
Neutralization titration:
E = E lg [H+]
Metal
electrode
Complexometric titration:
E = E lg [Mn+]
0.059 n
Ion-selective
electrode
Precipitation titration:
E = E lg [X−]
Nobel metal
electrode
[ox]
[red]
Redox titration:
E = E lg
0.059 n

17. POTENTIOMETRY Neutralization analysis
Indicator electrode:
External
reference electrode
Glass electrode
GLASS ELECTRODE
Outline
INSTRUMENTAL
DETECTION
H+ conc. to be determined
Electrochemical cell for measurement of pH:
Advantages
Types
Potentiometric end point detection
Conductometric end point detection
External reference ||
electrode ||
(Hg/Hg2Cl2/KCl) ||
H+ conc. |
to be |
determined |
pH-sensitive |
glass- |
membrane |
Internal |
buffer sol. |
(KCl) (pH = 7) |
Internal reference
electrode
(Ag/AgCl/KCl)
███████████
External Dry glass Internal
hydrated hydrated
gel layer gel layer

18. POTENTIOMETRY Glass electrode
Composition of glass:
E.g. 22 % Na2O, 6 % CaO, 72 % SiO2.
Na+ mobile
membrane
Outline
solution H+
Na+
Ion-exchange reaction:
between
H+ in the solution and
Na+ in the glass: H+
Na+ H+
Na+
INSTRUMENTAL
DETECTION K
H+ + Na+Gl−  Na+ + H+Gl– K = LARGE!
solution glass solution glass
Advantages
Types
Potentiometric end point detection
Conductometric end point detection
Combination glass electrode:

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

20. CONDUCTOMETRIC TITRATION CURVES
I. Titration of strong acid (a) with strong base e.g. HCl with NaOH
(b) with weak base e.g. HCl with NH4OH
Outline
INSTRUMENTAL
DETECTION %
Advantages
Types
Potentiometric end point detection
Conductometric end point detection
II. Titration of weak acid (c) with strong base e.g. CH3COOH with NaOH
(d) with weak base e.g. CH3COOH with NH4OH %