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Chapter 7 Electrochemistry. § 7.3 Applications of Conductivity Measurement. Main contents: Monitoring the purity of water Measurement of ionizability Determine solubility product and ionic product Conductometric titration. Silicon wafer. 1. Monitor the purity of water. Group works: - PowerPoint PPT Presentation
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Chapter 7 Electrochemistry
§7.3 Applications of Conductivity Measurement
Main contents:
1) Monitoring the purity of water
2) Measurement of ionizability
3) Determine solubility product and ionic product
4) Conductometric titration
Main contents:
1) Monitoring the purity of water
2) Measurement of ionizability
3) Determine solubility product and ionic product
4) Conductometric titration
1. Monitor the purity of water
Group works:
Calculate the conductivity of pure water.
at 25 oC, Kw = 10-14, [H+] = [OH] = 10-7 mol·dm-3
water Tap
water
Distilled
water
Deionized
water
Pure
water
/S·m-1 1 10-2 ~1 10-3 <1 10-4 5.478 10-6
Fabrication of VLSI
Silicon wafer
In-situ monitoring of the cleaning process :
H2O2/H2SO4 DW rinse dilute HF SC-1 cleaning
DW rinse hot DW rinse DW rinse SC-2 cleaning DW rinse dilute HF DW rinse.
DW - deionized water, SC-1: H2O2/NH3;
SC – standard cleaning, SC-2: H2O2/HCl.
2. Measure the ionizability and dissociation constant
m
( )c Z F U U
c
c+ = c
m ( )U U F
At infinite dilution
m ( )F U U
m
m
( )
( )
U U F
U U F
Arrhenius suggested that the degree of dissociation of an electrolyte can be calculated using molar conductivity.
+AB A + B
0 0
(1 )
c
c c c
2 2 2m
m m m(1 ) 1 ( )
cc cK
c
Ostwald dilution law
Ostwald showed how one can measure the dissociation constant of an acid.
The equation can be rearranged to
m2m m m
1 1 1( )
a
cK
mc
m
1
m
1
2m
1
( )a
SK
Linearization
3. Determine solubility and solubility products
-Ag Ag Cl Cl H H OH OHc c c c
w Ag Ag Cl Cl Ag Cl( )c c S
w w
mAg Cl
S
Example:
The conductivity of a saturated AgCl solution is 1.86 10-4 S·m-1, while that for water is 6.0 10-6 S·m-1. Molar conductivity of AgCl is 0.01372 S·mol-1·m2. Calculate the solubility product for AgCl.
5. Determine ion product of water
Water can be taken as a dilute solution of a strong electrolyte
CH+ = COH- = Kw1/2
m m,H m,OHc
The specific conductance of highly purified water is 5.478 10-6
S·m-1. Calculate the concentration of hydrogen ion in water.
-1 2m m,H m,OH
0.05481S mol m
6 14 3
1 2m
7 3
5.478 10 S m0.9995 10 mol m
0.05481S mol m
1 10 mol dm
c
6. Conductometric titration
The conductance variation of a solution during titration can serve as a useful method to follow the course of the reaction.
Na+ + OH- + (HCl) =
5.19 20.52
Na+ + Cl- +(H+ + Cl-)
5.19 7.91 36.30
Precipitation reactions, neutralization reactions, and
coordination reactions
Ionic mobility of ions:A
B
C
A’B’
C’
V / ml
/ S
·m-1
endpoint