1 electrolysis using electrical energy to produce chemical change. sn 2+ (aq) + 2 cl - (aq) --->...
TRANSCRIPT
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ElectrolysisElectrolysisUsing electrical energy to produce chemical change.
Sn2+(aq) + 2 Cl-(aq) ---> Sn(s) + Cl2(g)
SnSnClCl22
SnClSnCl22(aq)(aq)
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.
44
Electrolysis of Molten NaClElectrolysis of Molten NaCl
Figure 20.14Figure 20.14
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 (-).
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.
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.
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
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
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.