1. Marti Andreski De La Salle HS

2. A Physics Student’s Guide to Electrochemistry A typical electrochemical cell (voltaic cell)…A typical electrochemical cell (voltaic cell)… Has two “” – one tends to give up electrons, one tends to take on electrons. This is the very meaning of “potential difference”, which is also voltage.Has two “electrodes” – one tends to give up electrons, one tends to take on electrons. This is the very meaning of “potential difference”, which is also voltage.

3. The “Players”… connects a strip of Zn with a strip of Cu A wire... The Zn is immersed in ZnSO 4 The Cu is immersed in CuSO 4 The 2 solutions are connected by a “Salt Bridge”, completing the circuit but preventing the sol’n from mixing ANIMATION: http://www.chem.iastate.edu/ group/Greenbowe/sections/pr ojectfolder/animations/CuZnc ell.html http://www.chem.iastate.edu/ group/Greenbowe/sections/pr ojectfolder/animations/CuZnc ell.html

4. Whenever Two Metals… …combine, one always has a greater ability to give up electrons than the other. Therefore, that’s exactly what happens… the one with the greater ability to LOSE electrons is OXIDIZED.…combine, one always has a greater ability to give up electrons than the other. Therefore, that’s exactly what happens… the one with the greater ability to LOSE electrons is OXIDIZED. When Zn and Cu combine, it’s the Zn that has the greater ability to LOSE electrons. 2e- When the charge reaches the Cu, Cu +2 ions come out of solution and combine with the e-’s to make Cu metal Cu +2 Cu As Zn loses e-, Zn metal becomes Zn +2 and goes in to solution. The “half cell” rxn is: Zn 0  Zn +2 +2e- and Zn is oxidized (or wears away) Zn +2 The Cu, then, is said to be electronically “reduced” since it goes from Cu +2 + 2e-  Cu 0 (Cu “builds up” on the Cu electrode)

5. Over Time… …the Zn electrode wears away, and the Zn +2 becomes more concentrated in the ZnSO 4 solution,…the Zn electrode wears away, and the Zn +2 becomes more concentrated in the ZnSO 4 solution, …while more and more Cu +2 ions come out of solution, combining with electrons and forming more Cu metal (“plating” of Cu on Cu) Zn +2 Zn +2

6. More easily oxidized (Give up e- easier) More easily reduced (Take up e- easier)

7. Using the SRP Chart to Determine Cell Voltage The pair combined is Zn and Cu There are 3 locations for Cu; which is used? We have to know the reaction. Cu +2 ions are coming out of solution and becoming Cu metal, so… Cu +2 + 2e-  Cu Since Zn is higher on the table, it is the oxidized half; Cu is reduced. NOTE: is the form Zn +2 + 2e-  Zn written as an oxidation? (LOSS OF e- = oxidation!)

8. SRP : 25 o C and 1.0M aqueous Li + + e-  Li(s) -3.05 Cs + + e-  Cs(s) -2.92 K + + e-  K(s) -2.92 Rb + + e-  Rb(s) -2.92 Ba 2+ + 2 e-  Ba(s) -2.90 Sr 2+ +2 e-  Sr(s) -2.89 Ca 2+ + 2 e-  Ca(s) -2.87 Na + + e-  Na(s) -2.71 Mg 2+ + 2 e-  Mg(s) -2.37 Be 2+ + 2 e-  Be(s) -1.70 Al 3+ + 3 e-  Al(s) -1.66 Mn 2+ + 2 e-  Mn(s) -1.18 Zn 2+ + 2 e-  Zn(s) -0.76 Cr 3+ + 3 e-  Cr(s) -0.74 Fe 2+ + 2 e-  Fe(s) -0.44 Cr 3+ + e-  Cr 2+ -0.41 Cd 2+ + 2 e-  Cd(s) -0.40 Tl + + e-  Tl(s) -0.34 Co 2+ + 2 e-  Co(s) -0.28 Ni 2+ + 2 e-  Ni(s) -0.25 Sn 2+ + 2e-  Sn(s) -0.14 Pb 2+ + 2 e-  Pb(s) -0.13 (this may be easier to read when printed) 2 H + + 2 e-  H 2 (g) 0.00 S(s) + 2 H + + 2 e-  H 2 S (g) 0.14 Sn 4+ + 2 e-  Sn 2+ 0.15 Cu 2+ + e-  Cu+ 0.15 Cu 2+ + 2 e-  Cu(s) 0.34 Cu + + e-  Cu(s) 0.52 I 2 (s) + 2 e-  2 I - 0.53 Fe 3+ + e-  Fe 2+ 0.77 Hg 2 2+ + 2 e-  2 Hg(l) 0.79 Ag + + e-  Ag(s) 0.80 Hg 2+ + 2 e-  Hg(l) 0.85 2 Hg 2+ + 2 e-  Hg 2 2+ 0.92 Br 2 (l) + 2 e  2 Br - 1.07 O 2 (g) + 4 H + + 4 e-  2 H 2 O(l) 1.23 Cl 2 (g) + 2 e-  2 Cl - 1.36 Au 3+ + 3 e-  Au(s) 1.50 Co 3+ + e-  Co 2+ 1.82 F 2 (g) + 2 e-  2 F - 2.87

9. Shorthand & Calculations Rb|Rb + ||Fe +3 |FeRb|Rb + ||Fe +3 |Fe What is the expected voltage if Cr and K make an electrochemical cell?What is the expected voltage if Cr and K make an electrochemical cell? Now, Work on your handout.Now, Work on your handout.