1. ELECTROLYSIS

2. molten OUTCOME QUESTION(S): C12-6-09 CELLS AND POTENTIALS
Explain the operation of a voltaic (galvanic) cell at the visual, particulate and symbolic level.
Include: writing half-cell reactions and overall reaction
Calculate standard cell potentials and predict spontaneity of reactions.
Compare and contrast voltaic (galvanic) and electrolytic cells.
Vocabulary & Concepts
molten

3. Process of using electricity to force a nonspontaneous reaction
Electrolysis: “electro” – electricity
“lysis” – break
Electrolytic cells
Process of using electricity to force a nonspontaneous reaction
Different: it is nonspontaneous so the opposite metals are going to be reduced and oxidized from a voltaic cell
A battery is needed to add energy and it must be attached to inert electrodes
Different: inert electrodes do not take
part in reaction – don’t “plate out” or “lose mass”

4. Anions migrate to (+) anode and are oxidized
Inert electrodes must be charged to attract the appropriate ions to the appropriate side
Different: electrodes oppositely charged
Same: e- still flow from anode to cathode
Same: anode oxidized, cathode reduced
Anions migrate to (+) anode and are oxidized
Cations migrate toward (-) cathode to be reduced

5. 1. Molten Electrolytic Cells
most metals occur naturally as compounds
NaCl , Cu2O, TiO2 , CuF2
Unwanted elements of a compound are called “impurities”
forcing the non-spontaneous redox is a common process for obtaining pure elements
Need very high temperatures to make salts molten - “melt”

6. Na+(l) + Cl–(l) → Na (s) + Cl2(g)
Down's Cell:
Na+(l) + Cl–(l) → Na (s) + Cl2(g)
2 Cl-(l) → Cl2(g) + 2e-
2 Na+(l) + 2e-→ 2 Na(s)
EoO = V
Notice: stronger element – Cl is oxidized
EoR = V
Notice: weaker element – Na is reduced
Eocell = V
PURE
PURE
A battery must supply 4.07 V of power to make this electrolytic cell work

7. Electrolysis of water: Water can be both reduced and oxidized
Oxidation:
2 H2O(l) → 4 H+(aq) + O2(g) + 4e–
Reduction:
4 H2O(l) + 4e– → 4 OH–(aq) + 2 H2(g)
Net:
6 H2O(l) → 2 H2(g)+ O2(g) +
4 H+(aq) + 4 OH–(aq) 2
These ions recombine to form 4 H2O
Overall: 2 H2O(l) → 2 H2(g)+ O2(g)

8. 2. Aqueous Electrolytic Cells:
3 possible reactants that will compete for
electrons - cations, anions and water
Because water is present – and it can oxidize and reduce – you might not get what you expected in the reaction…
Must predict which substance is most likely
to be oxidized and which is reduced
This is done by comparing the oxidation and reduction potentials of all possible reactants

9. Possible reactants: K+ I– H2O
What are the products formed at each electrode during the electrolysis of aqueous KI?
Possible reactants: K+ I– H2O
K+ cannot lose more electrons:
Only I – and H2O can be oxidized
Oxidization:
2 I–(aq) → I2(s) + 2e– E°o = – 0.54V
H2O(l) → 2 H+(aq) + ½ O2(g) + 2e– E°o = –1.23V
I- has most positive oxidation potential
solid iodine is formed at the anode

10. Overall: 2 H2O(l) + 2 I–(aq) → H2(g) + I2(s)
Possible reactants: K+ I– H2O
I- cannot gain more electrons:
Only K+ and H2O could be reduced
Reduction:
K+(aq) + 1e– → K(s) E°R = – 2.93V
2 H2O(l) + 2e– → 2 OH-(aq) + H2(g) E°R = – 0.83V
H2O has most positive reduction potential
hydrogen gas is formed at the cathode
Overall: H2O(l) I–(aq) → H2(g) + I2(s)
Spectator ions created in the reaction would be K+ and OH-

11. object to be plated – cathode desired metal – anode
Electroplating:
Battery used to plate layer of metal onto another surface by reducing its own ions.
object to be plated – cathode
desired metal – anode
immersed in a solution of same metal ions
Only one element – the metal is oxidized at the anode, then reduces itself at the cathode item

12. reaction of metals with oxygen - spontaneous
Corrosion:
reaction of metals with oxygen - spontaneous
metal – oxidized oxygen – reduced
Most metals have reduction potentials below oxygen – except gold
Sacrificial anode – second “weaker” element that sacrifices its electrons and oxidizes to save metal

13. molten CAN YOU / HAVE YOU? C12-6-09 CELLS AND POTENTIALS
Explain the operation of a voltaic (galvanic) cell at the visual, particulate and symbolic level.
Include: writing half-cell reactions and overall reaction
Calculate standard cell potentials and predict spontaneity of reactions.
Compare and contrast voltaic (galvanic) and electrolytic cells.
Vocabulary & Concepts
molten