Practical Applications of Electrochemistry
A) Commercial Electrochemical Cells
There are three main types of commercial electrochemical cells:
1) Primary Cells
Definition
Example
Diagram
Cathode Halfreaction
Anode Halfreaction
Voltage
Electrolyte
Advantages
Disadvantages
Alkaline dry cell.
2) Secondary Cells
Definition
Example
Diagram
Cathode Halfreaction
Anode Halfreaction
Voltage
Electrolyte
Advantages
Disadvantages
Lead-acid storage battery.
3) Fuel Cells
Definition
Example
Diagram
Cathode Halfreaction
Anode Halfreaction
Voltage
Electrolyte
Advantages
Disadvantages
Hydrogen-oxygen fuel cell.
Additional Questions
1. In order to be rechargeable, the products of discharging must be stable and must be able to
travel through the electrolyte back to the appropriate electrode.
a) Given the anode and cathode half-reactions for a lead-acid storage battery, write the
balanced redox equation for discharging and recharging and indicate whether these
reactions are endo or exothermic, spontaneous or non-spontaneous.
Anode:
Cathode:
Pb(s) + HSO4- ----> PbSO4(s) + H+ + 2ePbO2 (s) + HSO4- + 3H+ + 2e- -- PbSO4 (s) + 2H2O(l)
Redox Reaction
Endo/
Exo ?
Spont.
or Not?
Discharging
Recharging
b) What voltage does this cell provide?
c) What would happen if one of the Pb plates was bent and touched one of the PbO2 plates?
2. Consider the hydrogen-oxygen fuel cell:
a) Write the overall reaction for the hydrogen-oxygen fuel cell.
b) What advantages do fuel cells have over fossil fuel combustion methods of generating
electricity?
B) Corrosion and Prevention
The oxidation of most metals is called ______________________________. The
oxidation of iron is called ____________________________. The two major causes of
rusting are _____________________ and
_________________________.
When a drop of water sits on iron a spontaneous redox reaction occurs.
Corrosion:
Fe
Prevention:
1) Barrier Methods
Work by preventing __________________ and ___________________
from coming into contact with the iron.
Can apply a layer of ____________________ or ____________________ or can apply
a layer of a corrosion _______________________ metal like _________. Tin oxidizes
to form a protective _________________________________ layer which adheres
tightly to the underlying metal and prevents further corrosion. If the tin oxide layer is
scratched however, corrosion will occur.
2) Electrochemical Methods
i) Cathodic Protection – attach a metal like _______ or
_______ that is more easily ________________ than
iron. The magnesium or zinc will be oxidized instead of
the _____________ and the ______ produced will
flow over the iron preventing it from
_______________________. The magnesium and zinc are called ________________
_____________________. The method above is used on small boats. On large ships a
low voltage ________________ is applied to the hull to force ________ onto the metal
and prevent it from ________________.
ii) Galvanizing – the iron is coated with ____________. Zin _____________________
more readily than ____________ forming a layer of _________________________
which protects the iron. Even when the zinc layer is scratched, it will protect the iron.
C) The Breathalyzer Test
The breathalyzer used by police uses a redox
reaction. When the alcohol is consumed a small
amount can be detected in the person’s
___________________. When you breathe into a
breathalyzer the alcohol in your breath reacts with
an acidified ______________________ solution.
The acidified dichromate (orange) acts as an
________________________ agent and the
alcohol acts as a ________________________
agent. One of the products of this reaction is
__________ which is ___________________. An
instrument measures the change in color from
orange to green which is translated into a bloodalcohol measurement. The reaction is: