1. Redox Reactions Electrolytic Cells
Mr. Shields Regents Chemistry U14 L04

2. Electrolytic Cells Earlier we said there were two types of Cells:
- Electrochemical (i.e. voltaic/galvanic cell)
- Electrolytic cell
Electrochemical cells produce electricity through a
Spontaneous Redox reaction.
In an ELECTROLYTIC CELL, electrons (i.e. electricity) are
provided to drive a non-spontaneous Redox reaction

3. Electrolytic Cell Usage
Electrolytic cells are typically used to:
- plate metals on other metals
- obtain a pure metal from it’s compounds
- recharge batteries

4. Differences between Electrochemical Cells
Electrolytic Cells are different from Voltaic Cells because …
They need Electricity to force a redox rxn to occur
There is an external power source req’d
They don’t produce electricity
The polarities are reversed (we’ll see why later)
The Anode is positive
The Cathode is negative
Electrolytic cell reactions are also different because they usually take place in one solution/one cell

5. Electrolysis In this example A battery supplies Electrons to drive
Let’s look at the electrical decomposition of water. This is
an example Of an electrolytic cell. It’s called ELECTROLYSIS
2H20(l)  2H2(g) + O2(g)
In this example
A battery supplies
Electrons to drive
The non-spontaneous
Reaction forward
What If we drew this
electrolytic cell,
What would it look
Like?

6. - Notice that oxidation still takes place at the anode and
Reduction still takes place at the Cathode.
BUT … now the
Anode is positive
And the cathode
Is negative.
2O-2 O2 +4e-
Battery feeds
e- into cell + -
Electrons from an
External source
Flow into the
Cathode making it
Negative.
Electrons flow from
The anode into
The external power source
Making this electrode positive
O H2

7. Memory Jogger Remember our phrase for recalling characteristics of
An electrochemical (Voltaic) cell?
“ An Ox ate a Red Pussy Cat”
Well there’s another one for an electrolytic cell to
also help you remember.
“A POX on Electrolytic cells”
Anode
Positive
Oxidation
The Cathode is then just
the opposite
Cathode / Negative / Reduction

8. Electrode Comparison Voltaic Cell Electrolytic Cell Anode Negative
Positive
Cathode
Oxidation takes place
Reduction takes place

9. Other Electrolytic Cells
Remember we said earlier that Electrolytic cells are typically used to …
- plate metals on other metals
- obtain pure elements from compounds
- recharge batteries
We’re going to look at two of these processes:
- Production of pure elements
- Mainly Group elements
- Downs Cell
- Metal Plating

10. Electroplating
This is another example of an electrolytic cell. It is used
To plate one metal over another conducting object.
For example:
To plate Ag over
Stainless steel
To plate Au over Cu
Or Ni
To plate Cr over Fe

11. Electroplating - + In this diagram what is: The Cathode The Anode
At what electrode
Does Ox. Occur
At which electrode
Does Red. Occur
What are the half
Cell reactions?
Cr  Cr+2 +2e- + -
What’s plated
Chrome Electrode
Cr+2 +2e-  Cr
Chrome electrode
What’s plated

12. Downs Cell (fused Salt)+
Simplified
Cell
All reactive
Group 1 +2 metals,
F2 & Al Are
produced
This way.
If Na is being produced
At the cathode then
NaCl is melted (Fused)
(801 deg C)
To produce a different
Metal I need to use a
fused salt of that metal -

13. PROBLEM
A manufacturer wants to make Gold forks out of
his more cheaply made stainless steel (Fe) forks. Draw
An electrolytic cell that he could use to accomplish this
Task. Assume Au forms Au+3. Label everything fully
and specify the oxidation and reduction half cell
reactions that will take place.