Electrolysis Industrial Uses Electrode Products
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Transcript of Electrolysis Industrial Uses Electrode Products
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ELECTROLYSIS
Module C2
Splitting up ionic compounds (F)
Molten compounds
Ionic solutions & discharge rules
Q = It and OILRIG
Brine and purifying copper
+
-
+
-+
-+
-
+-+
-+ +
-
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Cl- ION
Na+
ION
SPLITTING UP IONIC COMPOUNDS 1
Ionic compounds (eg sodium chloride) are made from:
POSTIVE IONS (atoms which LOST negative electrons)NEGATIVE IONS (atoms which GAINED negative electrons)
As these ions have OPPOSITE CHARGES they attract each
other strongly to form IONIC BONDS
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SPLITTING UP IONIC COMPOUNDS 2
2 ways to split up the ions:
-+ +
- + --+ +
- + -
+
-
+
-+
-+
-
+-
+
-+ +
-
MELT
+ --
+
+--+
- +
DISSOLVE
H2O800C 20C
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SEPARATING THE IONS 1
+_
Battery pulls
electrons off one
electrode and
pushes them
onto the other
Metal
ELECTRODEELECTRON
This IS SHORT OF
electrons so becomes
POSITIVELY CHARGED
ANODE
This HAS EXTRAelectrons so becomes
NEGATIVELY CHARGED
CATHODE
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+
+ -
+- +
-
-
+
- -+ +
-
+
MOLTEN IONIC
COMPOUND
+ ANODE - CATHODE
When the battery is switched on,the + IONS move to the CATHODE
the IONS move to the + ANODE
SEPARATING THE IONS 2
This gives a way to SPLIT UP IONIC COMPOUNDS: ELECTROLYSIS
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Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt)
+
Cl-
Cl
-
Cl-
Cl
-
ClCl
Cl Cl
- =chloride ION,
extra 1 electronCl- Cl
chlorine ATOM,
NEUTRALCl Cl Cl2
molecule
- chloride IONS
lose their extraelectrons and
turn into neutral
chlorine ATOMS
At ANODE: Cl- e- + Cl
then: Cl + Cl Cl2 (gas)
Both together:
2Cl- 2e- + Cl2
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Na+
Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt)
+
At CATHODE: Na+ + e- Na
Na+
Na+ Na+
Na
NaNa
Na
= sodium ION,missing1 electron
sodium ATOM,
NEUTRALNa++ Na
+ sodium IONS
gain an extra
electron and turn
into neutral
sodium ATOMS
molten sodium
metal sinks to
bottom
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Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt)
MOLTEN
SODIUM
CHLORIDE
+ ANODE - CATHODE
CHLORINE
gas Cl2
SODIUM
metal Na
At ANODE:
Cl- e- + Cl At CATHODE:Na+ + e- Na
Cl + Cl Cl2 (gas)
ELECTRONS
Cl- Na+
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Example 2: Splitting up MOLTEN LEAD BROMIDE PbBr2
MOLTEN
LEAD
BROMIDE
+ ANODE - CATHODE
BROMINE
gas Br2
LEAD
Metal Pb
At ANODE:
Br- e- + Br At CATHODE:Pb2+ + 2e- PbBr + Br Br2 (gas)
ELECTRONS
Br- Pb2+
Both together:
2Br- 2e- + Br2
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What happens when the ionic compounds are dissolved
in water?
Here, water molecules break up into HYDROGEN IONS, H+
and HYDROXIDE IONS OH-
H2O H+ + OH-So, in an ionic solution (eg sodium chloride solution), there will be
FOUR types of ion present:
TWO from the ionic compound and TWO from the water (H+ + OH-)
SODIUM CHLORIDE
SOLUTION NaCl (aq)
Cl-
Na+
OH- H+Na+
Cl-OH-H+
H+
OH- Cl-
Na+
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IONIC SOLUTION
Cl-
Na+
OH- H+Na+
Cl-
OH-
H+
H+
OH- Cl- Na+
Which ions gain or lose electrons (get discharged)
and which stay in solution?
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IONIC SOLUTIONS: At the CATHODE
+
At CATHODE: 2H+ + 2e- H2
sodium ION,
missing 1
electron
Hydrogen ATOM,
NEUTRALNa+ H
Na+
Na+
H+
H+
H
H
H+hydrogen ION,
missing 1
electron
As HYDROGEN is
LESS REACTIVE
than SODIUM, it is
discharged. The
sodium ions stay in
solution.
which
ions?
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+
Cl-
Cl-
Cl-
Cl-
ClCl
Cl Cl
chloride ION,
extra 1 electronCl- Cl
chlorine ATOM,
NEUTRAL
At ANODE: 2Cl- 2e- + Cl2
IONIC SOLUTIONS: At the CATHODE halogen compounds
If the ion is a
HALOGEN (Cl, Br, I)it is discharged and
chlorine (or Br or I)
is given off and the
OH-
ions stay insolution
OH
O HOH
O H
O Hhydroxide ION,
from water
extra electron
which
ions?
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+ ANODE
Attracts ions (Anions)
If ions are HALOGENS ie
chloride Cl-
bromide Br
-
iodide I-
the HALOGEN is produced.If ions are NOT HALOGENS
Eg sulphate SO42-
,
nitrate NO3-
carbonate CO32-
OXYGEN is produced.
- CATHODE
Attracts + ions (Cations)
If + ions (metals) are MORE
REACTIVE than hydrogen
K, Na, Ca, Mg, Zn, Fe
Then HYDROGEN is
produced
If + ions (metals) are LESS
REACTIVE than hydrogen
Cu, Ag, Au
Then the METAL is produced
RULES FOR IONIC SOLUTIONS
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potassiumchloride
Compound State Anode(+)
Cathode(-)
Ions
molten K+Cl- potassium
chlorine
aluminiumoxide
molten Al3+O2- aluminium
oxygen
copperchloride solution Cu
2+
Cl
-
H
+
OH- copper chlorinesodiumbromide
solution Na+Br-
H+ OH-hydrogen
bromine
silver nitrate solution Ag+NO3- H+
OH-silver oxygen
potassiumchloride
solution K+Cl- H+
OH-hydrogen
chlorine
zinc sulphate solution Zn+SO42- H+
OH-
hydrog
en
oxygen
(REACTIVITY: K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+Cu2+ Ag+ Au3+ )
(REACTIVITY: K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+
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ELECTROLYSIS makes a CIRCUIT
Complete electric circuit:
Current carried by:
ELECTRONS in electrodes/wires
IONS in the electrolyte
To DOUBLE the MASS of substance
discharged at electrodes:
2 x CURRENT (2x batt. voltage)2 x TIME current flows for
(Q = I t)
-
+
+-
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Cl-
Cl-
Cl-
Cl- Na+ Na+
Na+ Na+
OILRIG
-ions LOSING electrons
to become atoms is calledOXIDATION
(even though oxygen may
not be involved)
+ ions GAINING electrons
to become atoms is calledREDUCTION
Oxidation is loss,
reduction is gain
OILRIG
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INDUSTRIAL ELECTROLYSIS OF BRINE
ANODE
OH- and Cl-
2Cl- 2e- + Cl2
OH-
left in solutionso concentration
grows
CATHODE
H+ and Na+
2H+ + 2e- H2
Na+
left in solutionso concentration
grows
Chlorine gas Hydrogen gas
Sodiumchloridesolution(neutral)slowly
changed to
BRINE(NaCl solution)
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Industrial chlorine production from electrolysis of
brine
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IMPURE COPPER
ANODE
PURE COPPER
CATHODECopper sulphate
CuSO4 solution
PURIFYING COPPER
Cu2+
Cu
CuCu2+ Cu2+Copper atoms
from impure
copper areOXIDISED to
copper ions
Copper ions transported
from anode to cathode
Copper ions
from impure
copper are
REDUCED to
copper atoms
As the atoms of the impurities are not
transported, the copper that builds up on the
anode is extremely pure.
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IMPURE
COPPER
ANODE
PURE
COPPER
CATHODE
IMPURE
COPPER
ANODE
PURE
COPPER
CATHODE
Over time, the impure anode dissolves away and the
impurities sink to the bottom. The pure cathode grows as
more pure copper is deposited on it.
Why will the concentration of the solution stay the same?