Lecture 9 pH measurement, connection with thermodynamics &amp; corrosion

# Lecture 9 pH measurement, connection with thermodynamics & corrosion

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Review from last lecture… The cell potential of any electrochemical cell is the sum of the half cell potentials for the oxidation and reduction half cells. E cell = E red + E ox Half cell potentials are typically reported in a table of reduction potentials. For a given process, E = E red . To calculate a cell potential, we must add E and E red , but do NOT adjust for amount (cell potential is an intensive property) The cell potential is directly related to change in Gibbs Free Energy ଴.଴ହଽଶ At 298 K: E cell = E red,cathode E red,anode Text uses: Nernst Equation:

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Electrochemical pH Measurement An interesting use of the Nernst equation is in the electrochemical determination of pH. CHM139 F2011 Jockusch Electrochemistry L8 2 For H 2 ( g ) 2 H + ( aq ) + 2 e , with P H 2 = 1 atm ܧ = 0.0592 ܸ × ݌ܪ The potential of this half cell reaction depends linearly on the pH!
Electrochemical pH Measurement The pH of an unknown solution can then be calculated by measuring the cell potential between a reference cell (of known potential) and the solution of unknown concentration. reference cell [H + ] = ? H 2 ( g ) 2 H + ( aq ) + 2 e E ox = 0.0592× pH E cell = cathode anode E red = E ref

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Electrochemical pH Measurement The following cell has a potential of 0.55 V at 25°C Pt( s ) | H 2 (1 atm) | H + (? M) || Cl (1 M) | Hg 2 Cl 2 ( s ) | Hg( l ) (E red = 0.28 V) What is the pH of the solution at the anode?
Electrochemical pH Measurement In practice, the anode is typically a glass electrode (AgCl coated

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## This note was uploaded on 12/15/2011 for the course CHM 139 taught by Professor Browning during the Spring '08 term at University of Toronto- Toronto.

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Lecture 9 pH measurement, connection with thermodynamics & corrosion

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