134p11m - 4/22/11 1 2 ATTENTION Schedule Change ! Checkout...

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4/22/11 1 1 2 3 ATTENTION Schedule Change !!!!!!!! Checkout Week including Final Quiz is moved to: May 2 – May 5 Make-ups will be administered on: Monday, May 2 at 5:30 PM Make-ups are only for students who have excused absences on 1 or more exercises. Students who cannot make the May 2 make-up date must inform Dr. Akhtar next week, Apr 11 - 14 4 5 There is a misprint in the written procedure Would be E obs = E B - E A (we don’t multiply E’s by n or m) On page 146, line 9 should read: 6 Objective: Examine electrical consequences of some chemical reactions and derive some chemically significant information from electrical measurements 1. Concentration dependence of the electrochemical potential confirming the Nernst equation for concentration cells both qualitatively and quantitatively . 2. Determining the solubility products of a silver halide measuring low concentrations electrochemically 3. Determining some standard reduction potentials and the relative oxidation/reduction capability of some metals
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4/22/11 2 7 Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag (s) Δ G = Δ Gº + RT ln Q Δ Gº = ± RT ln K eq K eq = e ± Δ Gº/RT Δ Gº = ± 88.7 kJ/mol R = 0.0083145 kJ/(mol K) T = 25 ºC = 298 K [Cu 2+ ] [Ag + ] 2 8 Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag (s) Substance Δ f (kJ/mol) Ag + ( aq ) 77.1 Ag ( g ) 246.0 Ag ( s ) 0.0 Cu + ( aq ) 50.0 Cu 2+ ( aq ) 65.5 Cu ( g ) 297.7 Cu ( s ) 0.0 Δ Gº = Σ Δ f,products - Σ Δ f,reactants Δ Gº = [(65.5) + (0.0)] – [(0.0) + (2 × 77.1)] = - 88.7 kJ/mol Gilbert et al. Chemistry , 2 nd Ed. (2009). 9 Cu (s) + 2 Ag + Cu 2+ + 2 Ag (s) 2 Ag + + 2 e - 2 Ag Cu Cu 2+ + 2 e - Cathode : the electrode to which cations flow to be oxidized e.g., Ag + Ag Anode : the electrode to which anions flow to be reduced e.g., Cl - Cl 2 10 Cu (s) Cu 2+ (aq) + 2e - e - + Ag + (aq) Ag (s) e - We want to know the potential (V) before any reaction takes place: V = i × R (from Ohm’s Law). 11 The voltmeter we use is the pH meter – a highly appropriate device. The pH meter has an exceptionally high resistance (10 – 100 Mohms) so very little current flows when a voltage is applied to it. Therefore,
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134p11m - 4/22/11 1 2 ATTENTION Schedule Change ! Checkout...

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