Titrations -II

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Lecture 8

• Titrations -II

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Conc. H2SO4 catalyst
gt300o C
All N ? NH4
C?CO2
Kjeldahl digestion
H?H2O
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NH3 H?NH4
NH3H2O
If HCl
Excess of H can be titrated with NaOH
NaOHNH3
If boric acid
HCl or H3BO3
B(OH)4- H? H3BO3 H2O
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Precipitation Titration
AgNO3 NaCl ? AgCl NaNO3 Ag Cl- ? AgCl
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AgCl ? Ag Cl-
KSP AgCl-
pX - log10X
pAg - log10Ag
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Na
Na
NO3-
NO3-
Cl-
n-
Cl-
Na
Na
Cl-
Cl-
NO3-
AgNO3
AgNO3
AgCl
Cl-
AgCl
Cl-
Cl-
Cl-
Na
Na
Na
soluble
Na
NO3-
Colloid
equivalence point coagulation
In the middle
_at_ first drops
no chloride ion left in solution, no further
precipitation possible
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Titration of NaCl with AgNO3
C0.1 M
Cl-10-4 M ?Ag1.8?10-6 M
Equivalence point AgCl-
99.9 Ag
Acceptable end point
100.1 Ag
Ag10-4 M
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I- Ag ? AgI
pAg -logAg
99.9 Ag
Ksp(AgI)AgI-8.3?10-17
Acceptable end point
100.1 Ag
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Precipitation titration with silver electrode
The change of V is proportional to pAg
V(mV)
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I-
I-
Ind2-
_
_
_
_
_
_
I-
_
_
I-
Ind2-
Ind2-
Ag
Ag




Ind2-




Ag

Ag
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Precipitation Titrations