19.1 STANDARD ELECTRODE POTENTIALS [VOLTAIC (Spontaneous) Electrochemical Cells]
*Voltaic cell animations: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf
*An arrangement of _____ half–cells that can produce electricity _______________________.
*A complete _______can be split into two parts connected by a porous boundary or ______ bridge. Each part is called a
half-cell. (*a group of two or more cells connected in series = a ___________)
*Half-cell  consists of an ____________ (___________ or ___________) and an __________________
*Ex. of VOLTAIC Cell:
Ex. Shorthand Voltaic cell notation:
*VOLTAIC Cells Connected in Series (i.e. a battery)
Zn(s)  ZnSO4(aq)  CuSO4(aq)  Cu(s)
*Half-cell #1 = Electrode = _________ ; Electrolyte = ___________
*Half-cell #2 = Electrode = _________ ; Electrolyte = ___________
*In a Voltaic cell the anode is labeled ____________ and the cathode is the labeled ____________.
EX. VOLTAIC Cell Activity: Draw and label a Silver-Copper Voltaic Cell after completing the following:
Shorthand Notation:
Net Notation:
*Voltaic Pile
*DETERMINING THE REACTIONS IN A VOLTAIC CELL (Memorize the Following Procedure/Theory):
METHOD 1:
*Using your Data booklet or p.____ of your text, determine the strongest oxidizing agent present in the cell.
*SOA in previous example = ______
*The SOA always undergoes ________________at the ____________. (SOARC)
*Remember: “REDuction CAThode”; Cathode = electron “_________”
*Determine the strongest reducing agent present in the cell. *SRA = ______
*The SRA always undergoes _______________ at the ______________.
*Remember: “ANode OXidation” ; Anode = electron “ ___________”
*Electrons released by ________ travel through a wire to the ___________ where they are accepted by the _________.
The energy produced by the electron flow can be harnessed and used to do work.
*Electrons always move from the __________ towards the ___________. (a c)
METHOD 2:
Strongest Reducing Agent = MOST REACTIVE METAL = ANODE
*FUNCTION OF THE SALT BRIDGE (…a hollow“U” shaped-tube) …or porous boundary
 The salt bridge contains a solution. (Solute = inert salt such as potassium nitrate, KNO 3)
 Without the salt bridge, current quickly _________________.
 enables electrolyte solution to maintain neutrality (i.e. prevents ___________________ )
 anions migrate to the _____________ via the salt bridge (to offset the buildup of __________)
 cations migrate to the _____________(to offset the buildup of __________as more and more of the OA is reduced)
*This process gives the impression that negative charges are attracted to the negatively labeled ________, and that positive charges
are attracted to the positively labeled _____________.
Standard Cells and Cell Potentials
*What is meant by Standard Cell?
Standard Cell = a cell where both the reactants and products are in their standard states
i.e. – solutes at ______ mol dm-3 concentrations
- gases at pressure of _____ kPa
- solids and liquids in their pure form, all at a temperature of ______°C / _______ K(elvin)
e.g. - E° for the reaction
Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)
metal electrodes and 1 mol dm-3 concentrations of Zn2+ and Cu2+.
is the cell potential measured at 25°C for a cell that has pure
Standard Reduction Potentials (Er˚)
 the Er˚ represents the ability of a standard half-cell to attract electrons in a reduction half reaction; these are the values found at the
far left of the table next to each particular half-reaction
Standard Cell Potentials (ΔE˚cell)
 the ____________ (i.e. the maximum potential difference) of a cell operating under standard conditions
Memorize this formula!...
ΔE˚cell =
(i.e. Standard cell potential = the difference between the reduction potentials of the two standard half-cells…the voltage)
*Simple translation: Voltage = Larger Er˚ – Smaller number Er˚
More Regarding Standard Electrode Potentials (E°r)
HINTS:
 All reactions are written as reductions.
 The Standard Hydrogen Electrode (SHE electrode) is defined as ___________ V (something had to be…see below).
 There are two important reactions with water – highlight them. They occur at -0.83 V and +1.23 V. (More on these later.)
 There are three different reactions of copper – make sure you pick the right one!
 A number of entities (H2O, Cu+, Sn2+, Cr2+, Fe2+) can behave as oxidizing agents or reducing agents.
 Obey significant figures when working out cell potentials – keep 2 decimal places.
The STANDARD HYDROGEN HALF-CELL
*Standard reduction electrode potentials are measured RELATIVE TO
THE STANDARD HYDROGEN ELECTRODE HALF-CELL.
NOTATED: Pt(s H2(g), H+(aq)
2H+(aq) + 2e- <===>
H2(g)
Er˚ = 0.00 V
The inert electrode, _________________, in contact with 1 mol dm-3
hydrogen ion and hydrogen gas at 100 kPa and 298 K.
SUMMARY (“SHE” ELECTRODE)
- inert platinum electrode
- [H+] = 1 mol dm-3
- H2(g) at 100 kPa and 298 K
- E° = 0.00 V
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/electroChem/voltaicCell20.html
EXAMPLES: