Upload
herbert-powers
View
225
Download
2
Tags:
Embed Size (px)
Citation preview
What does this?
Have to dowith this?
NOTHING!!!
B/ Electrolytic Cells: Electrolysis - when an electric current is used to force a redox reaction that is normally
nonspontaneous to occurThey convert electrical energy chemical energy
Like voltaic cells, electrolytic cells have:a. redox reactions involving electrons
b. an anode where oxidation takes place because electrons are removed (lost) from there
c. a cathode where reduction takes place because electrons are moved (gained) there
d. electrons flowing from anode to cathode
battery+ -
Unlike voltaic cells,electrolytic cells have these differences:a. A battery or other source of electrical energy must be used because the reaction is nonspontaneous.b. The anode is now positive (+), and the cathode is now negative (-). This is the opposite of a voltaic cell.c. Both oxidation and reduction occur in the same cell.
anode cathode
e-
+ -
Diagram of anelectrolytic cell:
e-
Uses of Electrolytic Cells:
Ex. Electrolysis of molten salts to produce active metals:
2NaCl(l) + 2Na(l) + Cl(g)
Oxidation at the anode: 2Cl- Cl2 + 2e-
Reduction at the cathode: 2Na+ + 2e- 2Na
electrical energy
Uses of Electrolytic Cells:
Ex. Electrolysis of molten salts to produce active metals:
2NaCl(l) + 2Na(l) + Cl(g)
Oxidation at the anode: 2Cl- Cl2 + 2e-
Reduction at the cathode: 2Na+ + 2e- 2Na
Ex. The electrolysis of water:
2H2O(l) + 2H2(g) + O2(g)
Notice that twice as many hydrogen molecules as oxygen molecules are produced.
In both examples, electrical energy is a “reactant.”
electrical energy
electrical energy
The half reactionsin the electrolysisof H2O are notas simple as other examplesseen so far:
At the anode: 2H2O O2 + 4H+ + 4e-
At the cathode: 4H+ + 4e- 2H2
Ex. Electroplating – During electrolysis, a layer of a second metal can be deposited on the metal cathode.The purpose is to:
1/ improve the appearance of objects 2/ protect them from corrosion.
Silver baris a sourcefor platingthe spoon.
A steelspoon isthe objectto be plated.
At the silver bar, the neutral solid silver is oxidized: Ag(s) Ag+ + e-
The electrons are attracted to the positive side of the battery. The Ag+ ions enter solution and are attractedto the negative spoon.
Ex. Electroplating – During electrolysis, a layer of a second metal can be deposited on the metal cathode.The purpose is to:
1/ improve the appearance of objects 2/ protect them from corrosion.
Silver baris a sourcefor platingthe spoon.
A steelspoon isthe objectto be plated.
At the silver bar, the neutral solid silver is oxidized: Ag(s) Ag+ + e-
The electrons are attracted to the positive side of the battery. The Ag+ ions enter solution and are attractedto the negative spoon.
When they reach the steel spoon, the Ag+ ions gain electrons that come from the negative side of the battery and are reduced to solid silver:
Ag+ + e- Ag(s)This solid silver plates (covers) the steel spoon.
The battery holds the anode at a positivepotential and the cathode at a negative potential.
This is the opposite of a voltaic cell.
Ex. Electroplating – During electrolysis, a layer of a second metal can be deposited on the metal cathode.The purpose is to:
1/ improve the appearance of objects 2/ protect them from corrosion.
Silver baris a sourcefor platingthe spoon.
A steelspoon isthe objectto be plated.