1 electrolysis using electrical energy to produce chemical change. sn 2+ (aq) + 2 cl - (aq) --->...
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ElectrolysisElectrolysisUsing electrical energy to produce chemical change.
Sn2+(aq) + 2 Cl-(aq) ---> Sn(s) + Cl2(g)
SnSnClCl22
SnClSnCl22(aq)(aq)
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22Electrolysis of Aqueous Electrolysis of Aqueous NaOHNaOH
Anode (+) Anode (+)
4 OH4 OH-- ---> --->
OO22(g) + 2 H(g) + 2 H22O + 4e-O + 4e-
Cathode (-) Cathode (-)
4 H4 H22O + 4e- ---> O + 4e- --->
2 H2 H22 + 4 OH + 4 OH--
EEoo for cell = -1.23 V for cell = -1.23 V
Electric Energy ----> Chemical ChangeElectric Energy ----> Chemical Change
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ElectrolysisElectrolysisElectric Energy ---> Chemical ChangeElectric Energy ---> Chemical Change
BATTERY
+
Na+Cl-
Anode Cathode
electrons
BATTERY
+
Na+Cl-
Anode Cathode
electrons• • Electrolysis of Electrolysis of
molten NaCl.molten NaCl.
• • Here a battery Here a battery
“pumps” electrons “pumps” electrons
from Clfrom Cl-- to Na to Na++..
• • Polarity of Polarity of
electrodes is electrodes is
reversed from reversed from
batteries.batteries.
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Electrolysis of Molten NaClElectrolysis of Molten NaCl
Figure 20.14Figure 20.14
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55Electrolysis of Molten Electrolysis of Molten NaClNaCl
Anode (+) Anode (+)
2 Cl2 Cl-- ---> Cl ---> Cl22(g) + 2e-(g) + 2e-
Cathode (-) Cathode (-)
NaNa++ + e- ---> Na + e- ---> Na
BATTERY
+
Na+Cl-
Anode Cathode
electrons
BATTERY
+
Na+Cl-
Anode Cathode
electrons
EEoo for cell (in water) = E˚ for cell (in water) = E˚cc - E˚ - E˚aa
= - 2.71 V – (+1.36 V)= - 2.71 V – (+1.36 V)
= - 4.07 V (in water)= - 4.07 V (in water)
External energy needed because EExternal energy needed because Eoo is (-). is (-).
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66Electrolysis of Aqueous Electrolysis of Aqueous NaClNaCl
Anode (+) Anode (+)
2 Cl2 Cl-- ---> --->
ClCl22(g) + 2e-(g) + 2e-
Cathode (-) Cathode (-)
2 H2 H22O + 2e- ---> O + 2e- --->
HH22 + 2 OH + 2 OH--
EEoo for cell = -2.19 V for cell = -2.19 V
Note that HNote that H22O is more O is more easily reduced easily reduced than Nathan Na++. .
BATTERY
+
Na+Cl-
Anode Cathode
H2O
electrons
BATTERY
+
Na+Cl-
Anode Cathode
H2O
electrons
Also, ClAlso, Cl-- is oxidized in is oxidized in preference to Hpreference to H22O because of O because of
kinetics.kinetics.
Also, ClAlso, Cl-- is oxidized in is oxidized in preference to Hpreference to H22O because of O because of
kinetics.kinetics.
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77Electrolysis of Aqueous Electrolysis of Aqueous NaClNaCl
Cells like these are the source of NaOH and ClCells like these are the source of NaOH and Cl22..
In 1995: 25.1 x 10In 1995: 25.1 x 1099 lb Cl lb Cl22 and 26.1 x 10 and 26.1 x 1099 lb NaOH lb NaOH
Also the source of NaOCl for use in bleach.Also the source of NaOCl for use in bleach.
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88Electrolysis of Aqueous Electrolysis of Aqueous NaINaI
Anode (+): Anode (+): 2 I2 I-- ---> I ---> I22(g) + 2e-(g) + 2e-
Cathode (-): Cathode (-): 2 H2 H22O + 2e- ---> HO + 2e- ---> H22 + 2 OH + 2 OH--
EEoo for cell = -1.36 V for cell = -1.36 V
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99Electrolysis of Aqueous Electrolysis of Aqueous CuClCuCl22
Anode (+) Anode (+)
2 Cl2 Cl-- ---> Cl ---> Cl22(g) + 2e-(g) + 2e-
Cathode (-) Cathode (-)
CuCu2+2+ + 2e- ---> Cu + 2e- ---> Cu
EEoo for cell = -1.02 V for cell = -1.02 V
Note that Cu is more Note that Cu is more
easily reduced than easily reduced than
either Heither H22O or NaO or Na++. .
BATTERY
+
Cu2+Cl-
Anode Cathode
electrons
H2O
BATTERY
+
Cu2+Cl-
Anode Cathode
electrons
H2O
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1010Electrolytic Refining of Electrolytic Refining of
CopperCopper
Figure 22.11, page 934Figure 22.11, page 934
Impure copper is oxidized to CuImpure copper is oxidized to Cu2+2+ at the anode. at the anode. The aqueous CuThe aqueous Cu2+2+ ions are reduced to Cu metal ions are reduced to Cu metal at the cathode.at the cathode.
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Producing AluminumProducing Aluminum2 Al2 Al22OO33 + 3 C ---> 4 Al + 3 CO + 3 C ---> 4 Al + 3 CO22
Charles Hall (1863-1914) developed Charles Hall (1863-1914) developed electrolysis process. Founded Alcoa.electrolysis process. Founded Alcoa.