Transcript Voltaic Cells - EARJ Chemistry

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Voltaic Cells
or Batteries
• Rechargeable batteries power a great deal of the
electronics we use today, including cordless phones, cell
phones and laptop computers. Voltaic cells, as well as
various other electrolytic cells, are used in these
rechargeable batteries
• Make your own iPod/iPhone/GPS/etc… battery-pack and
recharger! The charger circuitry and 2 AA batteries fit
into an small space such as an Altoids gum or mint tin,
and will run your iPod for hours, 2.5x more than you’d
get from a 9V USB charger! You can use rechargeable
batteries too.
Recycling cell phones
http://atitudesustentavel.uol.com.br/blog/2012/09/25/empresa-recolhe-celulares-para-reciclagem/
Voltaic Cells
• Invented by Alessandro Volta in
1800.
• Voltaic cells: electrochemical
cells used to convert chemical
energy into electrical energy
• A voltaic cell is an electrochemical cell that
uses a chemical reaction to produce
electrical energy. The important parts of a
voltaic cell:
• The anode is an electrode where oxidation occurs.
• The cathode is an electrode where reduction occurs.
• A salt bridge is a chamber of electrolytes necessary to
complete the circuit in a voltaic cell.
• The oxidation and reduction reactions are separated into
compartments called half-cells.
• The external circuit is used to conduct the flow of
electrons between the electrodes of the voltaic cell.
• A light bulb is a example of a
simple load where current
(a flow of electrons) is used
to resistively heat a filament
of metal, usually tungsten,
until it radiates energy in the
form of visible light.
Zn and Cu Cell
How does it work?????
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chapter_18&folder=zinc_copper_cell
• If we are using two metals such as Zn and
Cu, we must decide which one will
undergo oxidation and which will undergo
reduction by looking at the reduction table:
Zn+2 + 2e => Zn
Cu+2 + 2e => Cu
-0.76v
+0.34v
Cu2+ has a greater tendency to be reduced.
Zn will be oxidized.
Steps of a Voltaic Cell
• e- created at anode
– Shown in oxidation
half-reaction
• e- leave zinc and
pass through wire
• e- enter cathode
and cause
reduction
– Shown in halfreaction
• Positive and
negative ions pass
through salt bridge
to finish the circut
Figure 21.5
A voltaic cell based on the zinc-copper reaction.
Oxidation half-reaction
Zn(s)
Zn2+(aq) + 2e-
Reduction half-reaction
Cu2+(aq) + 2eCu(s)
Overall (cell) reaction
Zn(s) + Cu2+(aq)
Zn2+(aq) + Cu(s)
Voltaic Cell Shorthand
• Oxidation half cell is listed first with
reduced and oxidized species
separated by a line.
• Reduction is next in the opposite order.
• Double line separates the two and
represents a salt bridge.
Zn|Zn2+||Cu2+|Cu
Voltaic Cell Shorthand
• Draw shorthand notation for a
Mg-Pb cell where the nitrate ion
is present. You might want to
refer to the activity series to
determine what is oxidized and
what is reduced!
– Draw a diagram for this voltaic cell
• Label: anode, cathode, direction of eflow
• Write-out the ½ reactions and
combined reaction.
• If we are using two metals such as Mg and
Fe, we must decide which one will
undergo oxidation and which will undergo
reduction by looking at the reduction table:
Mg+2 + 2e => Mg
Fe+2 + 2e => Fe
-2.37v
-0.45v