Chapter 7 Electrochemistry § 7.3 Applications of Conductivity Measurement A B C A’ B’ C’ V / ml  / S·m - 1 endpoint

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 o C, K w = , [H + ] = [OH  ] = mol·dm -3 waterTap water Distilled water Deionized water Pure water  /S·m -1 1  ~1  <1   Fabrication of VLSI Silicon wafer

In-situ monitoring of the cleaning process : H 2 O 2 /H 2 SO 4  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: H 2 O 2 /NH 3 ; SC – standard cleaning, SC-2: H 2 O 2 /HCl.

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.

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

3. Determine solubility and solubility products Example: The conductivity of a saturated AgCl solution is 1.86  S·m -1, while that for water is 6.0  S·m -1. Molar conductivity of AgCl is S·mol -1 ·m 2. Calculate the solubility product for AgCl.

5. Determine ion product of water Water can be taken as a dilute solution of a strong electrolyte C H+ = C OH- = K w 1/2 The specific conductance of highly purified water is  S·m -1. Calculate the concentration of hydrogen ion in water.

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) = Na + + Cl - +(H + + Cl - ) Precipitation reactions, neutralization reactions, and coordination reactions Ionic mobility of ions: A B C A’ B’ C’ V / ml  / S·m -1 endpoint