1 electrolysis using electrical energy to produce chemical change. sn 2+ (aq) + 2 cl - (aq) --->...

11

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

33

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.

1111

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.