Galvanic%20Cells

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Galvanic Cells

• From Chemistry to Electricity

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Luigi Galvani

• Lived 1737-1798 in Bologna, Italy
• Physician
• During a dissection of a frog, his zinc scalpel
  and copper rod reacted to make the frogs leg
  jump
• Animal electricity

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The Galvanic Reaction
Blue
Invisible
Zn(s) Cu2(aq) ? Cu(s) Zn2(aq)
Grey metal
Red metal
Reduction Cu2(aq) 2 e- ? Cu(s)
Oxidation Zn(s) ? Zn2(aq) 2 e-
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The Galvanic Reaction in a Single Vessel
Cu2
Zn(s)
Cu2
Cu2
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The Galvanic Reaction in a Single Vessel
Cu2
Zn(s)
Cu2
Cu2
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The Galvanic Reaction in a Single Vessel
Cu2
Zn(s)
Cu(s)
Cu2
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The Galvanic Reaction in Two Vessels
Cu2
Zn(s)
Cu2
Cu2
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The Galvanic Reaction in Two Vessels
Conductor
Cu2
Zn(s)
Cu2
Cu2
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The Galvanic Reaction in Two Vessels
Conductor
Cu(s)
Zn(s)
Cu2
Cu2
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The Galvanic Cell
Current ?
Conductor
Cu2
Cu(s)
Zn(s)
Cathode
Anode
Cu2
Cu2
Oxidation happens at the anode
Reduction happens at the cathode
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The Galvanic Cell
A galvanic cell (also known as an electrochemical
cell) is made from two dissimilar metals
connected by a conductor and immersed in a
solution that contains ions. The metal strips
are called electrodes, and the solution is called
an electrolyte.
The anode is the electrode where oxidation
occurs. It loses electrons, which travel through
a circuit, and gradually decreases in mass. The
anode is always the stronger reducing agent of
the two metals. Anode and oxidation both start
with vowels.
The cathode is the electrode where reduction
occurs. It gains electrons from the circuit, and
gradually increases in mass. The cathode is
always the weaker reducing agent of the two
metals. Cathode and reduction both start with
consonants.
The electrons that travel through the circuit can
be forced to do work by passing them through a
load, such as a light bulb, buzzer, or diode. A
galvanic cell changes chemical energy into
electrical energy.
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The Salt Bridge
- - - - -

Cu(s)
Zn(s)
Cu2
Cu2
Anode
Cathode
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The Salt Bridge
The salt bridge prevents positive charge from
accumulating near the anode and negative charge
from accumulating near the cathode. It contains
both positive and negative ions that diffuse back
and forth to keep the overall charges equal.
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Practice

• Remember, you can make a galvanic cell out of any
  two metals, as long as they are far enough apart
  in the activity series. For each of the
  following pairs of metals
• 1. State which will form the anode, and which
  will form the cathode.
• Write the half reactions.
• Take the half reactions to the lowest common
  multiple, and add them together to get the
  overall cell reaction.
• Zinc and Nickel b) Magnesium and Silver
• c) Silver and Gold d) Pop Cans and Pennies
  (Aluminium and Copper)