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Electrochemistry

Electrochemistry. +. e -. K n+ + n e - K. e.g. Fe 2+ + 2e - Fe. Different forms of Nernst equation. Cation electrodes:. ox.form. red.form.  =  0 + (0.06/n)log.  n  / 1 .  =  0 + (0.06/n)log.  n  . 6. +. A n - A + n e -. e -.

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Electrochemistry

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  1. Electrochemistry

  2. + e- Kn+ + n e- K e.g.Fe2+ + 2e-Fe Different forms of Nernst equation Cation electrodes: ox.form red.form  = 0 + (0.06/n)log n/1  = 0 + (0.06/n)log n 6

  3. + An -A + n e- e- e.g. Cl -1/2 Cl2 + e- Anion electrodes: red.form ox.form (1/)  = 0+ (0.06/n)log  = 0- (0.06/n)log  8

  4. + Ox. form + n e- e- e.g. Fe3+ +e-Fe2+ Redox electrodes: red.form  = 0 + (0.06/n)log ( cox/cred) 9

  5. Kn+ + n e- K Fe3+ + 3e-Fe + Concentration dependence of electrode potential: CATION electrodes Decreasing conc. More negative e

  6. - Concentration cell made of cation electrodes e- + + + + + + + + + + e- e- Me Men+ Me Men+ red. form ox. form red. form ox. form - +1 12

  7. e.g.  C1 C2 Fe3+ +3e- Fe Fe Fe3+ +3e- Concentration cells made of CATION electrodes Fe/Fe3+ (0.2 M) Fe/Fe3+ (0.014 M) C1=0.2 M C2=0.014 M + - +=  + (0.06/3)log c1 -= eo + (0.06/3)lg c2 Emf = + - - = eo + (0.06/3)log c1 -eo- (0.06/3)log c2 Emf = (0.06/n)log(c1/c2) where c1 c2

  8. Generation of transmembrane potential Impermeable membrane “in” “out” 15 mM Na+Cl- 150 mM K+Cl- 150 mM Na+Cl- 15 mM K+Cl- Zero potential difference

  9. Generation of transmembrane potential “in” “out” 15 mM Na+Cl- 150 mM K+Cl- 150 mM Na+Cl- 15 mM K+Cl- - - - + + + Permeable to K+ only K+ Net charge Emf = (0.06/n)log(150/15)=60 mV

  10. Generation of transmembrane potential Permeable to Na+ only “in” “out” 15 mM Na+Cl- 150 mM K+Cl- 150 mM Na+Cl- 15 mM K+Cl- - - - + + + Na+ Net charge Emf = (0.06/n)log(150/15)=60 mV

  11. An -A + n e- Cl- 1/2 Cl2+ e- e- e 0 e e conc. 1.36 1,8 1.36 1.36 1,4 1.36 1.36 1 1.36 conc. 1.36 1.36 Concentration dependence of electrode potential: ANION electrodes Decreasing conc. More positive e  = +1.36 - (0.06)logCl –] 1 1.360 0.1 1.420 0.01 1.480 0.001 1.540 0.0001 1.600 1 0.00001 1.660 0.1 0.01 0.001 0.0001 0.00001 0.000001 0.000001 1.720 0.0000001 18 0.0000001 1.780

  12. Concentration cells made of ANION electrodes Cl2 Cl2 [ HCl ]=1 M [ HCl ]=0.1 M - + HCl HCl Cl- 1/2 Cl2 + e- 1/2 Cl2 + e- Cl-

  13. H+ + e- 1/2 H2 Concentration dependence of electrode potential: HYDROGEN electrodes ox.form red.form H2 Nernst equation:  = 0 + (0.06/1)log[H+]  = - 0.06 pH

  14. H+ + e - 1/2H2 + 0 e e pH e (V) 0 0 -0,2 0 0 0 -0,6 0 0 0 -1 The hydrogen electrode Decreasing conc. More negative e - 0.06 * pH  = 0 2 4 6 8 pH 10 12 14 0 0,00 2 -0.12 4 -0.24 6 -0.36 8 -0.48 10 -0.60 12 -0.72 14 -0.84

  15. > C1 C2 pH1 pH2 Concentration cells made of hydrogen electrodes 1/2 H2 | H+ (c1) 1/2 H2|H+ (c2) < Electrode process: H+ +e- 1/2 H2 1/2 H2  H+ + e- - + Emf = 0.06*lg(c1/c2) Emf = 0.06* pH

  16. [ionized] = [total] [H+] c Calculation of degree of ionization (a) from eH  = 0.06 x log [H+] a =

  17. Calculation of acid/base concentration from eH  = 0.06 x lg [H+] pH concentration

  18. Thank you for your attention! eH pH a

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