1 titration curves k (a) + (r) (p) (a) + (r) (p) analyte titrant product titration curves: 1. strong...
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1
TITRATION CURVESTITRATION CURVES K (A)(A) + + (R)(R) (P)(P)
analyte titrant product
Titration curves:Titration curves:1.1. Strong acidStrong acid with strong basestrong base,, Strong baseStrong base with strong acidstrong acid2.2. Weak acidWeak acid withstrong basestrong base,, Weak baseWeak base with strong acidstrong acid3.3. Polyprotic acidPolyprotic acid with strong basestrong base
Important points and Important points and regionsregions::2 points: before titrationbefore titration (at 0%) I.I. [[AA]]
at the end pointat the end point (at 100 %) III.III. [[AA]] = = [[RR]]2 regions: before the end pointbefore the end point (0.00..1 – 99.99…%) II.II. [[AA]] + + [[PP]]
after the end pointafter the end point (100.00..1 – ∞) IV.IV. [[PP]] + + [[RR]]
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
Outline
NEUTRALIZATION ANALYSISNEUTRALIZATION ANALYSIS
2
TITRATION CURVESTITRATION CURVES
I.I. At the start:At the start:
HCl HCl + + NaOHNaOH Cl Cl–– ++ NaNa++(H(H22O) O) acidacid11 + + base base22 basebase11 ++ acid acid22
(very weak)(very weak)
e.g.
1.1. Strong acidStrong acid with strong basestrong base,, Strong baseStrong base with strong strong acidacid
II.II. Before the end point:Before the end point: [H+] = [H3O+]=[HCl]unreacted [OH–] = [NaOH]unreacted
pH = – lg [HCl]unreacted pOH = – lg [NaOH]unreacted
III.III. At the end point:At the end point: [H+] ≡ [OH–]
KW = 10–14 pH ≡ 7IV.IV. After the end point:After the end point:
[OH–] = [NaOH]excess [H+] = [H3O+]=[HCl]excess
pOH = – lg [NaOH]excess pH = – lg [HCl]excess
OutlineNEUTRALIZATIONNEUTRALIZATION
ANALYSISANALYSIS
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
[H+] = [H3O+]=[HCl]0 [OH–] = [NaOH]0
pH = – lg [HCl]0 pOH = – lg [NaOH]0 pH = 14 – pOH
3
TITRATION CURVESTITRATION CURVES
1. Effect of the temperature:1. Effect of the temperature:
100100°C°C [H[H++]·[OH]·[OH––] = K] = Kww = 10 = 10–1–122 NNeeutr. pointutr. point: pH = 6: pH = 6
25°C25°C [H[H++]·[OH]·[OH––] = K] = Kww = 10 = 10–14–14 NeutrNeutr. po. poiint: pH = nt: pH = 77Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
100 0
Titration curves:Titration curves:1.1. Strong acid Strong acid with strong basestrong base,, Strong baseStrong base with strong acidstrong acid2.2. Weak acidWeak acid withstrong basestrong base,, Weak baseWeak base with strong acidstrong acid3.3. Polyprotic acid Polyprotic acid with strong basestrong base
EFFECTS ON THE TITRATION CURVE: EFFECTS ON THE TITRATION CURVE:
4
EFFECTS ON THE TITRATION CURVEEFFECTS ON THE TITRATION CURVE
2. Dependence on the initial concentrations (e.g. 2. Dependence on the initial concentrations (e.g. [[HClHCl]]):):
[HCl]0
↓
0% 50% 90% 99% 99.9% 100% 100.1% 101% 110%
1 N 0 0,3 1 2 3 7 11 12 13
0,1 N 1 1,3 2 3 4 7 10 11 12
0,01 N 2 2,3 3 4 5 7 9 10 11
0,001 N 3 3,3 4 5 6 7 8 9 10
ΔpH33 – – 11114 4 – – 101055 – – 9966 – – 88
pH change around the end point
100 0
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
Outline
5
3. Dependence on the acid strength (dissociation constants):3. Dependence on the acid strength (dissociation constants):
A. Weak acidA. Weak acid with strong basesstrong bases ,
EFFECTS ON THE TITRATION CURVEEFFECTS ON THE TITRATION CURVE
100 0
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
Outline e.g. 10–1 N CHCH33COOHCOOH is titrated with NaOH NaOH (Ka = 2x10–5)
%% 0 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
ΔpH pKInd ≈ 99 → PHENOLPHTALEINPHENOLPHTALEINB.B. Weak baseWeak base with strong acidstrong acid
%% 0 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 5 → METHYL REDMETHYL RED
e.g. 10–1 N NHNH44OH OH is titrated with HCl HCl (Kb = 2x10–5)
6
TITRATION CURVESTITRATION CURVES
I. At the start:I. At the start:
pH
II.II. Weak acid Weak acid with strong base strong base Weak baseWeak base with strong acidstrong acid
Weak acidWeak acid Weak baseWeak base
basebCKOH acida CKH COOHCHKH 3a OHNHKOH 4b
II. Before the end point:II. Before the end point:
pHBuffer (acid / salt)Buffer (acid / salt) Buffer (base / salt)Buffer (base / salt)
salt
acida C
CKH
salt
baseb C
CKOH
4
4b
NH
OHNHKOH
COOCH
COOHCHKH
3
3a
III. At the end point:III. At the end point:
pHHydrolysing salt (Brönsted base)Hydrolysing salt (Brönsted base) Hydrolysing salt (Brönsted acid)Hydrolysing salt (Brönsted acid)
salta
w CK
KOH
saltbCKOH COOCHKOH 3b
IV. After the end point:IV. After the end point:
pHExcess of strong baseExcess of strong base
[OH–] = Cexcess base [OH–] = [NaOH]excess[H+] = Cexcess acid [H+] = [HClexcess
Excess of strong acidExcess of strong acid
saltb
w CK
KH
salta CKH 4a NHKH
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
OutlineNEUTRALIZATIONNEUTRALIZATION
ANALYSISANALYSIS
e.g. Titration of CHCH33COOHCOOH with NaOH NaOH , Titration ofTitration of NHNH44OH OH with HCl:HCl:
7
TITRATION CURVES TITRATION CURVES III.III. Polyprotic acid Polyprotic acid with strong basestrong base
1.1. HH33POPO44 + + OHOH–– HH22POPO44– – + H+ H22OO Ka1 = 7x10–3
2.2. HH22POPO44–– ++ OHOH–– HPOHPO44
2–2– ++ HH22OOKa2 = 6x10–8
3.3. HPOHPO442–2– + + OHOH–– POPO44
33–– + + HH22OOKa3 = 10–12
e.g. Titration of H H33POPO44 with NaOHNaOH
Introduction
Titrants
Titration curvesTitration curves
End point detection
Applications
OutlineNEUTRALIZATIONNEUTRALIZATION
ANALYSISANALYSIS
8
ACID / BASE INDICATORSACID / BASE INDICATORS
1.1. Azo-compoundsAzo-compounds
Genearal structure:Genearal structure:
Mechanism:Mechanism:
Yellow Yellow (basic)(aromatic)
YellowYellow(intermediate) (protonated)
RedRed (acidic)(quinoid)
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Outline
Introduction
Titrants
Titration curves
End p. detectionEnd p. detection- chemical- chemical- instrumental
Applications
9
ACID / BASE INDICATORS ACID / BASE INDICATORS
2.2. PHTHALEIN-derivativesPHTHALEIN-derivativesGeneral structure:General structure:
Mechanism:Mechanism:
ColorlessColorless (acidic)
ColorlessColorless(intermediate)
PurplePurple (basic)
Thymol blueNEUTRALIZATIONNEUTRALIZATION
ANALYSISANALYSIS
Introduction
Titrants
Titration curves
End p. detectionEnd p. detection- chemical- chemical- instrumental
Applications
Outline
10
INSTRUMENTAL DETECTIONINSTRUMENTAL DETECTION
MethodMethod Sensing deviceSensing device Type of titrationType of titration
POTENTIOMETRYPOTENTIOMETRY
(Potential (Potential vs %)%)
Different types of
electrodeselectrodes
Neutralization titr.Neutralization titr.Complexometric titr.Complexometric titr.Precipitation titr.Precipitation titr.Redox titr.Redox titr.
The titration process is followed by electrochemical, photometric or other sensing devices.sensing devices.
(Summary)(Summary)
AMPEROMETRYAMPEROMETRY
(Current (Current vs %)%)
PtPt electrode
(dead stop…) Redox titr.Redox titr.
CONDUCTOMETRYCONDUCTOMETRY
(Conductivity (Conductivity vs %)%)Conductivity cellConductivity cell Neutralization titr.Neutralization titr.
Precipitation titr.Precipitation titr.
PHOTOMETRYPHOTOMETRY(A = (A = εε ·· c c ·· l l vs %)%)
SpectrophotometerSpectrophotometer Complexometric Complexometric titr.titr.
ENTALPHYMETRYENTALPHYMETRY(Q = f (c, (Q = f (c, ΔΔH) H) vs % %
ThermistorThermistor Neutralization titr.Neutralization titr.Complexometric titr.Complexometric titr.Precipitation titr.Precipitation titr.Redox titr.Redox titr.
Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
TypesTypes
Potentiometric end point detection
Conductometric end point detection
11
POTENTIOMETRYPOTENTIOMETRY
Nernst equation:Nernst equation:
Electrode potentialElectrode potential developed developedbetween:
Neutralization titration:Neutralization titration:
Complexometric titration:Complexometric titration: E = EE = E00 + lg + lg [[MMn+n+]]
Indicator electrodeIndicator electrode Reference electrodeReference electrode
Glass electrodeGlass electrode
MetalMetalelectrodeelectrode
Precipitation titration:Precipitation titration:
Redox titration:Redox titration:
E = EE = E00 + 0.059 lg + 0.059 lg [[XX−−]]
E = EE = E00 + lg + lg [[oxox]][[redred]]
Ion-selectiveIon-selectiveelectrodeelectrode
Nobel metalNobel metalelectrodeelectrode
Common reference electrodes:Common reference electrodes:Solid metal / its „unsoluble” salt / saturated conc. of anion
e.g. Ag / AgCl / KCl Hg / Hg2Cl2 / KCl Hg / Hg2SO4 / K2SO4
E = EE = E00 + 0.059 lg + 0.059 lg [[HH++]]
0.0590.059 nn
0.0590.059 nn
Known, constant potentialconstant potential (Eref) IndependentIndependent of theof the analyte concentrationconcentration
PotentialPotential (Eind) varies Depends onDepends on the analyte concentrationconcentration
Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
Types
Potentiometric Potentiometric end point end point detectiondetection
Conductometric end point detection
clgn
059.0EE 0
12
POTENTIOMETRYPOTENTIOMETRYNeutralization analysisNeutralization analysis
Indicator electrode:Indicator electrode:
GLASS ELECTRODEGLASS ELECTRODE
Electrochemical cell for measurement of pH:Electrochemical cell for measurement of pH:
Internal referenceInternal reference electrodeelectrode (Ag/AgCl/KCl)
InternalInternal ||
buffer sol.buffer sol. ||(KCl) (pH = 7) ||
pH-sensitivepH-sensitive || glass- glass- || membranemembrane ||
HH++ conc. conc. || to be to be ||determineddetermined ||
External referenceExternal reference |||| electrodeelectrode ||||(Hg/Hg2Cl2/KCl) ||||
███████████External Dry glass Internalhydrated hydratedgel layer gel layer
ExternalExternalreference electrodereference electrode Glass electrodeGlass electrode
H+ conc. to be determined
Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
Types
Potentiometric Potentiometric end point end point detectiondetection
Conductometric end point detection
13
POTENTIOMETRYPOTENTIOMETRYGlass electrodeGlass electrode
Composition of glass:Composition of glass:E.g. 22 % Na2O, 6 % CaO, 72 % SiO2.
Ion-exchange reaction:Ion-exchange reaction:between
HH++ in the solutionin the solution and NaNa++ in the glass in the glass:
Combination glass electrode:Combination glass electrode:
Na+ mobile
KKHH++ + + NaNa++GlGl−− NaNa++ + + HH++GlGl–– K = LARGE!K = LARGE!
solution glass solution glass
Na+H+
solution membrane
Na+H+
H+
Na+Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
Types
Potentiometric Potentiometric end point end point detectiondetection
Conductometric end point detection
14
POTENTIOMETRYPOTENTIOMETRYTitration curveTitration curve
Potentiometric titration curve:Potentiometric titration curve:
Measuring the potential potential of a suitable indicator electrode (pH)(pH) as a function ofof volume volume titrant.
Determination of the end point:Determination of the end point: from the derivativesderivatives
11stst derivative derivative
22ndnd derivative derivative
Titration curveTitration curve
Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
Types
Potentiometric Potentiometric end point end point detectiondetection
Conductometric end point detection
15
CONDUCTOMETRIC CONDUCTOMETRIC TITRATION CURVESTITRATION CURVES
I.I. Titration of Titration of strong acidstrong acid (a) (a) with strong basestrong base e.g. e.g. HClHCl with NaOH NaOH (b)(b) with weak baseweak base e.g. e.g. HClHCl with NHNH44OHOH
II.II. Titration of Titration of weak acidweak acid (c) (c) with strong basestrong base e.g. e.g. CHCH33COOHCOOH with NaOH NaOH
(d)(d) with weak baseweak base e.g. e.g. CHCH33COOHCOOH with NH NH44OHOH
%%
%%
Outline
INSTRUMENTALINSTRUMENTALDETECTIONDETECTION
Advantages
Types
Potentiometric end point detection
Conductometric end point detection
16
APPLICATIONSAPPLICATIONS
I. I. Determination ofDetermination of strong strong acidsacids / / basesbases:: Equivalence point:Equivalence point: pH = 7pH = 7
TITRATIONSTITRATIONS
DirectDirect Back (indirect):Back (indirect):
AnalyteAnalyteTitrant in excessTitrant in excess
to measureto measureto calculateto calculate
Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curves
End point detection
ApplicationsApplications
e.g. NaOHNaOH
VVphen.phen.
VVmeth.r.meth.r.
OHOH− − H H22OO
17
APPLICATIONSAPPLICATIONS
e.g. carboxylic acids of low carbon atoms carboxylic acids of low carbon atoms e.g. CH3COOH
II. (a)II. (a) Determination of Determination of weakweak acidsacids : :
e.g. CO CO22 (as carbonate or hydrogencarbonate)(as carbonate or hydrogencarbonate)
Application of COApplication of CO22 determination: determination:
DeterminationDetermination of of organic materialsorganic materials Determination ofDetermination of COCO22, HCO, HCO33
– – , CO, CO332–2–
content of natural waterscontent of natural waters
Distillation apparatusDistillation apparatus ((Maros- Schulek)Maros- Schulek)
Nonaqueous solvents:Nonaqueous solvents: KKa a << 10 10–7–7
>> 10 10–12–12
fatty acids fatty acids (e.g. fat, wax, oil)
Direct:Direct:
Back :Back : if the weak acid is if the weak acid is volatilevolatile
II.II. Determination ofDetermination of weakweak acidsacids : :
weak weak bases bases : : Equivalence point:Equivalence point: pH pH >> 7 7 (phenolphtalein indicator)(phenolphtalein indicator)
Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curves
End point detection
ApplicationsApplications
Equivalence point:Equivalence point: pH pH << 7 7 (methyl red indicator)(methyl red indicator)
Ka ≥ 10–5. (10–7 - 10–4)
bubble-freebubble-free distillationdistillationCOCO22 known amount of Ba(OH)Ba(OH)22
back titrationback titration of excessexcess Ba(OH)Ba(OH)22
with with standard HClHCl
18
APPLICATIONSAPPLICATIONS
Direct:Direct: e.g. NHNH44OHOH
Back:Back: NHNH44++ -salt -salt NHNH33
Application of NHApplication of NH33 determination: determination:
N-containing organic compounds N-containing organic compounds (e.g. amino acids, proteins,…)(e.g. amino acids, proteins,…)
strong base (NaOH)
boiling
Kjeldahl methodKjeldahl method::
Decomposition Decomposition (mineralization)(mineralization) withwith cc. H cc. H22SOSO44, 300 , 300 °°CC
+ catalyst: + catalyst: Se, or CuSe, or Cu2+2+
Ox. number:Ox. number: – 3– 3 (NH(NH44))22SOSO44 (e.g.. – NH2, –N(CH3)2, =NH, –N<)
Ox. number:Ox. number: + 3, +1+ 3, +1 HNOHNO33 (+5)(+5) (e.g.,azo- (-N=N-), nitro-, nitrozo comp.) ReductionReduction
with Zn, Nawith Zn, Na22SS22OO44,..,..
Nonaqueous solvents:Nonaqueous solvents: KKb b << 10 10–7–7
>> 10 10–12–12
NHNH44++
distillation distillation into into known excessknown excess of acid of acid Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curves
End point detection
ApplicationsApplications
II. (b)II. (b) Determination of Determination of weak weak basesbases : :Kb ≥ 10–5 (10–7 - 10–4)
NH3
known HCl
back titration of excess acid (HCl) with basic titrant (NaOH)
19
APPLICATIONSAPPLICATIONS
NOT MEASURABLE!NOT MEASURABLE!III.III. Determination of Determination of salts:salts:
E.g. Aniline Aniline ·· HCl HCl;; Benzidine Benzidine ··HH22SOSO44;; Papaverine Papaverine ·· HCl… HCl…
(a)(a) Neutral salts:Neutral salts:
(b)(b) Salt hydrolyzing to acid:Salt hydrolyzing to acid: Brönsted acid (strong acid + weak base)MA + H2O MOH + A– + HH++
if pK if pK >> 7 7! can be TITRATED! can be TITRATED with basewith base
(c)(c) Salt hydrolyzing to base:Salt hydrolyzing to base: Brönsted base Brönsted base (strong base + weak acid)MA + H2O HA + M+ + OHOH––
if pK if pK >> 7 7 can be TITRATED can be TITRATED with acid with acid
E.g.E.g. NaNa22BB44OO77 (B4O72– +7 H2O 4H3BO3 + 2OH–) methyl redmethyl red
Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curves
End point detection
ApplicationsApplications
E.g. NaNa22COCO33 (CO32– + H2O HCO3
– + OH–) phenolphtphenolpht..(CO3
2– +2 H2O H2CO3 +2 OH–) methyl redmethyl red
NaHCONaHCO33 (HCO3– + H2O H2O + CO2 +OH–) methyl redmethyl red
NaHCONaHCO33
VVmeth.r.meth.r.
HCOHCO33− − H H22COCO33
VVphenphen = 0 = 0COCO3322− − HCOHCO33
−− H H22COCO33
NaNa22COCO33
VVphenphen VVmeth.r.meth.r.
20
(d)(d) Specific determinations:Specific determinations: NaOH NaOH – Na– Na22COCO33
in the presence of each otherin the presence of each other
Outline
NEUTRALIZATIONNEUTRALIZATIONANALYSISANALYSIS
Introduction
Titrants
Titration curves
End point detection
ApplicationsApplications
APPLICATIONSAPPLICATIONS
OHOH−−, , COCO3322− − HCOHCO33
−− H H22COCO33
A. OH– + H+ H2O
Warder’s method :Warder’s method :
CO32– + H+ HCO3
–..B. HCO3
– + H+ H2CO3 methyl redmethyl red
one sample :one sample :
two samples :two samples :B. OH− + H+ H2O
CO32– +2H+ H2CO3
methyl redmethyl red
phenolpht.phenolpht.
Winkler’s method :Winkler’s method :A. + BaCl2
CO32– +Ba2+ BaCO3
OH– + H+ H2O phenolpht.
VVphenphen VVmeth.r.meth.r.
NaHCONaHCO33 – Na– Na22COCO33 in the presence of each otherin the presence of each other
Warder’s method :Warder’s method :two samples :two samples :
A. CO32– + H+ HCO3
–
phenolpht...B. HCO3
– + H+ H2CO3
CO32− +2H+ H2CO3
methyl redmethyl red
COCO3322−− HCOHCO33
− − HCOHCO33−− H H22COCO33
VVphenphen VVmeth.r.meth.r.
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