Chapter 7 Electrochemistry

§7.3 Applications of Conductivity Measurement

1. Monitor the purity of water

Silicon wafer

Integrated circuit

Fabrication of VLSI

§7.3 Applications of Conductivity Measurement

1. Monitor the purity of water Fabrication of VLSI

§7.3 Applications of Conductivity Measurement

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 ⎯ standard cleaning：

SC-1: H2O2/NH3; SC-2: H2O2/HCl.

1. Monitor the purity of water Fabrication of VLSI

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

§7.3 Applications of Conductivity Measurement

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.

§7.3 Applications of Conductivity Measurement

22 2 2

m

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

m2

m m m

1 1 1( )

a

cK

= +

Linearization

2. Measure the ionizability and dissociation constant

§7.3 Applications of Conductivity Measurement

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 of water used for preparation the

solution is 6.0 10-6 S·m-1. Given that the

molar conductivity of AgCl is 0.01372

S·mol-1·m2. Calculate the solubility

product for AgCl. What assumption have we made?

§7.3 Applications of Conductivity Measurement

4. 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 2

m m,H m,OH0.05481S mol m + −

= + =

6 1

1 2

m

4 3

7 3

5.478 10 S m

0.05481S mol m

0.9995 10 mol m

1 10 mol dm

c

− −

−

− −

− −

= =

=

§7.3 Applications of Conductivity Measurement

5. Conductometric titration (the way to determine endpoint)

The conductance variation of a solution

during titration can serve as a useful

method to follow the course of the

reaction.

Na+ + OH- + (HCl) = Na+ + Cl- + (H+ + Cl-)

5.19 20.52 5.19 7.91 36.30

Precipitation reactions,

neutralization reactions,

coordination reactions

A

B

C

A’

B’

C’

V / ml

/

S·m

-1

endpoint

§7.3 Applications of Conductivity Measurement

5. Conductometric titration

§7.3 Applications of Conductivity Measurement

6. Study on ionic channel in cell membrane

§7.3 Applications of Conductivity Measurement

6. Study on ionic channel in cell membrane

§7.3 Applications of Conductivity Measurement