Lecture 9 pH measurement, connection with thermodynamics & 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!
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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?
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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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