1. dia

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TITRATIONS IN NON-AQUEOUS SOLVENTS
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WATER, as SOLVENT
? cheap, clean (can easily be purified) ? high
relative permittivity (e) good solvent
ADVANTAGES
? 0 - 100 C temperature range ? apolar
substances can not be disolved ? Kw 10-14,
therefore Kd 10-7 unmeasurable
DISADVANTAGES
WATER actively participates in all type of
reactions
- acid and base acid-base reactions take place
through connection to water first (amphoteric)
- complex formation cations aqua
complex anions H-bond
- precipitation dissolves precipitate of ionic
lattice (high hydration energy)
- oxidant and reductant range of redox
potential 0 -1,23 V theoretical -0.8 - 2,1 V
practical
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CLASSIFICATION of SOLVENTS
ACIDIC (protogene) H2SO4, CH3COOH, HCOOH,
acetone proton donor
BASIC (protophyl) pyridine, liq. NH3, amins,
dioxane proton acceptor
AMPHOTERIC (amphiprotic) H2O, alcohols,
acetonitrile
APROTIC liquid SO2
INERT CCl4, CHCl3, benzene, carbohydrates
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REACTIONS in NON-AQUEOUS SOLUTIONS
? neutralization (protolytic solvents) 90 ?
complex formation, precipitation, redox 10
NEUTRALIZATION ANALYSIS in NON-AQUEOUS SOLVENTS
- pH scale depends on the value of KHL
H2LL-
AUTOPROTOLYSIS EQUILIBRIA determines the ionic
product
solvent K pH scale neutr. point
2 H2O ? H3O OH- 10-14 0 - 14 7
2 CH3COOH ? CH3COH2 CH3COO- 10-13 0 -
13 6,5
2 NH3 ? NH4 NH2- 10-32 0 - 32 16
2 C2H5OH ? C2H5OH2 C2H5O- 10-19 0 - 19 9,5
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REACTIONS in NON-AQUEOUS MEDIUM
- Brönsted equation can be used
- reactions take place through reaction of acids
or bases with the solvents
E.g. HClO4 pyridine (Py) in glacial acetic acid
K CH3COOH2CH3COO- 10-13
acid HClO4 CH3COOH ? ClO4- CH3COOH2
base Py CH3COOH ? PyH CH3COO-
ClO4- CH3COOH2 PyH CH3COO-
? PyH???ClO4- 2 CH3COOH
2 CH3COOH
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ADVANTAGES of USING NON-AQUEOUS SOLVENTS
? 1. More than 3 acids/bases can be measured in
mixture due to the wider pH range compared to
water
E.g.methyl-ethyl-ketone water 0 - 25.7 pH
range 0 - 14 pH range 5 comp. measurable max. 3
acids (3 x ?pH(4) 12) HClO4 - HCl - Salicylic
acid - Acetic acid - Phenol (can titrated with
TBAH (C4H9)4NOH-)
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ADVANTAGES of USING NON-AQUEOUS SOLVENTS
? 2. Differentiation - levelling effect (Kd
10-12 can be measured)
a) Differentiation effect
in water HClO4 HCl HNO3
in CH3COOH HClO4 gt HCl gt HNO3
in HF medium gt weak gt base
acid
Conclusions Strong acids (in water) can
separetely be measured in acidic solvents Strong
bases - ? -
in basic solvents
b) Levelling effect
in water HCl gt CH3COOH gt benzoic acid
in pyridine HCl CH3COOH benzoic
acid
Conclusions Weak acids (in water) can be
measured in basic solvents Weak bases
- ? - in acidic solvents
EXPLANATION by the protonaffinity
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ADVANTAGES of USING NON-AQUEOUS SOLVENTS
? 3. Determination of organic acids and bases
which have a limited solubility in water.
? 4. Application of new reagents and indicators
is possible due to
DISADVANTAGES of USING NON-AQUEOUS SOLVENTS
? expensive ? volatile ? toxic ? removal of
water is necessary, can take water (humidity)
from the air
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STANDARD SOLUTIONS
- HClO4 in glacial acetic acid - HCl in
propylene-glycol /chloroform mixture
ACIDIC
application - weak bases Kb 10-7 -
10-12 e.g. aromatic amines, amides,
alcaloides, etc. - high-molecular-weight
organic bases, that have limited solubility
in water
E.g. Determination of Lidocain (Lidocainum
Ph.Hg. VII.)
- TBAH (C4H9)4NOH-) in pyridine - KOH in ethanol
BASIC
application - weak acids Ka 10-7 -
10-12 e.g. carboxylic acids, phenols, enols
etc. - high-molecular-weight organic acids,
that have limited solubility in water
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END POINT DETECTION
- phtaleins (phenolphtalein) (e.g. in pyridine)
CHEMICAL (INDICATORS)
- azo compounds (methyl red) (e.g. in alcohol)
- crystal violet (in glacial acetic acid)
R ? C-R ? R
ibolya
R R-H 2 ? ? C-R H C -
R ? ? R R ibolya
zöldeskék
R R-H 2 R-H 3 ? ? ? C-R
H C - R H C-R ? ? ? R
R R-H violet green
yellow
- potentiomety glass electrode in glacial
acetic acid - conductometry
INSTRUMENTAL