Transcript Topic 10 - Making Electricity - St Thomas Aquinas RC Secondary

Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
In a battery the electricity comes from:
A chemical reaction.
Electricity passing along wires is:
A flow of electrons
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Batteries run out
When the chemicals in them are used up.
Some batteries can be recharged.
Like the lead/acid car battery
Or
The nickel/cadmium battery
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
An electrolyte is
A liquid that conducts electricity.
Batteries contain the electrolyte ammonium chloride.
Because it completes the circuit.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Electricity can be produced by battery or mains
Mains electricity is :Cheaper
Electricity from batteries is:
Safer – lower voltages
More portable
Both types use energy from fossil fuels
Batteries produce waste that damages the environment
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
A cell producing electricity can be made when
2 different metals are connected together with an
electrolyte.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
By connecting different pairs of metals we can produce an
Electrochemical Series
When set up in a cell:
A metal high in the series will send electrons to a
lower metal.
2 metals far apart in the series give a high voltage
2 metals close in the series give a low voltage.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Here is part of the Electrochemical Series.
The complete series is in the Data Book
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Potassium
P
Calcium
C
Sodium
S
Magnesium
M
Aluminium
A
Zinc
Z
Iron
I
Nickel
N
Tin
T
Lead
L
Hydrogen
H
Copper
Cu
Silver
Ag
Mercury
Hg
Gold
Au
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Redox Reactions
A REDOX reaction involves the 2 processes of
Oxidation and Reduction.
REDOX reactions involve a transfer of electrons.
O
Oxidation
I
Is
L
Loss of electrons
R
Reduction
I
Is
G
Gain of Electrons
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Cell Reactions
Mg  Mg2+ + 2e-
Pb2+ + 2e- -> Pb
Electrons flow through the wires from the higher metal to the
lower metal. (Mg to Pb)
Magnesium dissolves forming magnesium ions
Pb2+ ions (lead ions) move to the lead electrode
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Mg  Mg2+ + 2e-
Pb2+ + 2e- -> Pb
The ion bridge is there to complete the circuit.
The ion bridge allows ions to flow between the 2 solutions.
The magnesium dissolves away gradually and the lead gets
heavier as more lead ions turn into lead.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Displacement Reactions
A metal can displace a lower metal from a solution of
its compound.
Get Out copper!
OUT!
Magnesium displaces copper from copper sulphate solution
The products are magnesium sulphate and copper.
Mg (s) + CuSO4(aq)
-> MgSO4 (aq) + Cu(s)
The more reactive magnesium has pushed copper
out of its compound and taken its place.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Ion-electron equations
These show the oxidation and reduction steps in a
REDOX reaction.
Mg (s) + CuSO4(aq)
-> MgSO4 (aq) + Cu(s)
Magnesium is dissolving to form magnesium ions:
Loss of electrons
Mg (s)  Mg2+ (aq) + 2eOxidation
The copper ions in copper sulphate are turning
into copper metal.
Gain of electrons
Cu2+ (aq) + 2e-  Cu(s)
Reduction
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Electrolysis and ion-electron equations
Electrolysis is the breakdown of an ionic compound
using electricity.
Non-metals are discharged at the positive electrode.
Metals (and hydrogen) are discharged at the
negative electrode.
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
Electrolysis of Copper (II) Chloride
Copper ions go to the negative
electrode and form copper
Cu2+ (aq) + 2e-  Cu(s)
Gain of electrons - Reduction
Chloride ions go to the positive
electrode and form chlorine.
2Cl- (aq)
 Cl2 (g) + 2e-
Loss of electrons - Oxidation
Topic 10 - Making Electricity
B Gilday – St Thomas Aquinas Secondary
A Cell Without Metals
Electron flow
Carbon electrode
Carbon electrode
Solution of
iodide ions
Solution of iron
(III) ions
Ion bridge
Since electron flow is from left to right, iodide must lose electrons:
2I- (aq)  I2 + 2e-
Loss of electrons - Oxidation
Iron (III) ions must gain electrons:
Fe3+(aq) + e-  Fe2+(aq)
Gain of electrons - Reduction