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CHM 145 Lecture Notes - Lecture 23: Nernst Equation, Chemical Equation, Reference Electrode

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salmonwalrus328
24 Mar 2017
School
Oakland University
Department
Chemistry
Course
CHM 145
Professor
Charlene Hayden

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Document Summary

Standard electrode potentials: standard electrode potential (eo ) = the measured voltage for a half-reaction in which all reactants and products are their standard states. Standard reduction potential = eored: standard cell potential (eo cell) = the measured voltage for an electrochemical cell when all reactants & products are in their standard states. Eo cell = eo cathode (cid:886)o anode: standard states = concentrations are 1m and the partial pressure of gases are 1 atm. E cell = e she (cid:886) zn = (cid:865). (cid:865)(cid:865) (cid:903) (cid:886) zn = +0. 76 v thus, e zn = (cid:865). (cid:872)(cid:871) (cid:903) Note: the sign of e indicates the direction of spontaneity! Standard electrode potentials at 25 c: ~ (cid:899)(cid:914)(cid:927)(cid:920)(cid:918): (cid:860)(cid:868). (cid:865) (cid:933)(cid:928) (cid:868). (cid:865) (cid:903, higher up (closer to +3. 0) means reduction is more spontaneous. Stronger oxidizing agent: l(cid:928)(cid:936)(cid:918)(cid:931) (cid:917)(cid:928)(cid:936)(cid:927) (cid:857)(cid:916)(cid:925)(cid:928)(cid:932)(cid:918)(cid:931) (cid:933)(cid:928) (cid:868). (cid:865)(cid:858) (cid:926)(cid:918)(cid:914)(cid:927)(cid:932) (cid:928)(cid:937)(cid:922)(cid:917)(cid:914)(cid:933)(cid:922)(cid:928)(cid:927) (cid:922)(cid:932) (cid:926)(cid:928)(cid:931)(cid:918) (cid:932)(cid:929)(cid:928)(cid:927)(cid:933)(cid:914)(cid:927)(cid:918)(cid:928)(cid:934)(cid:932).

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Related Questions

The saturated calomel electrode, abbreviated SCE,Β  is often used as a reference electrode in making electrochemical measurements. The SCE is composed of mercury in contact with a saturated solution of calomel Hg2Cl2. The electrolyte solution is KCl. ESCE is +0.242 V relative to standard hydrogen electrode.

Calculate the potential for each of the galvanic cells containing a saturated calomel electrode and the given half-cell components at standard conditions. In each case indicate whether the SCE is the cathode or the anode. Standard reduction potentials are found in table:

Electrode

SCE

 a) Cu2+ + 2e- β†’ CuΒ  b) Fe3+ + e- β†’ Fe2+ c) AgCl +Β e- β†’ Ag + Cl- d) Al3+ + 3e- β†’ AlΒ  e) Ni2+Β + 2e- β†’ Ni
Eo

+0.242 V

 + 0.339 V + 0.771 V + 0.223 V - 1.677 V - 0.257 V

Given the measured cell potential is -0.3509V at 25°C in the following cell, calculate the H plus concentration. The balance reduction half reactions for the cell and their respective standard reduction potential values are in the picture.
  1. The half-reactions in a Galvanic cell are the following (ortheir reverse):

Sn4+(aq) + 2e- ?Sn2+(aq) (Eo = 0.13 V) (I)

MnO4-(aq) + 8H+(aq) +5e- ? Mn2+(aq) +4H2O(l) (Eo = 1.51 V) (II)

(a) Select the reduction process that is more favorable. (b) Whatreaction occurs at the anode of the cell? (c) What reaction occursat the cathode? (d) Write a balanced equation for the overall cellreaction. (e) What is the standard cell potential?