1. §7.3 Applications of Conductivity Measurement
Chapter 7 Electrochemistry
§7.3 Applications of Conductivity Measurement
Main contents:
Monitoring the purity of water
Measurement of ionizability
Determination of solubility product and ionic product
Conductometric titration

2. /S·m-1 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
Distilled
Deionized
Pure
/S·m-1
1 10-2
~1 10-3
<1 10-4
5.478 10-6
Fabrication of VLSI
Silicon wafer

3. 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.

4. 2. Measure the ionizability and dissociation constant
c+ = c
At infinite dilution
Arrhenius suggested that the degree of dissociation of an electrolyte can be calculated using molar conductivity.

5. The equation can be rearranged to
Ostwald showed how one can measure the dissociation constant of an acid.
Ostwald dilution law
The equation can be rearranged to
mc
Linearization

6. 3. Determine solubility and solubility products
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 S·mol-1·m2. Calculate the solubility product for AgCl.

7. 5. Determine ion product of water
Water can be taken as a dilute solution of a strong electrolyte
CH+ = COH- = Kw1/2
The specific conductance of highly purified water is 10-6 S·m-1. Calculate the concentration of hydrogen ion in water.

8. 6. Conductometric titration
The conductance variation of a solution during titration can serve as a useful method to follow the course of the reaction. A B C A’ B’ C’
V / ml
 / S·m-1
endpoint
Ionic mobility of ions:
Na+ + OH- + (HCl) =
Na+ + Cl- +(H+ + Cl-)
Precipitation reactions, neutralization reactions, and coordination reactions

10. Homework
Due time: Sep. 24