Electrolysis application of electrical current to produce a non spontaneous redox reaction
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Electrolysis – Application of electrical current to produce a non-spontaneous redox reaction. The electrochemical cell in electrolysis is termed an electrolytic cell as compared to a voltaic or galvanic cell in which a

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Electrolysis application of electrical current to produce a non spontaneous redox reaction
Electrolysis – Application of electrical current to produce a non-spontaneous redox reaction.

The electrochemical cell in electrolysis is termed an electrolytic

cell as compared to a voltaic or galvanic cell in which a

spontaneous reaction occurs.

The voltage necessary to produce a non-spontaneous reaction

must be greater than the value of Ecell for the competing

spontaneous reaction.


Example Problem: produce a A zinc electrode immersed in 1 M zinc sulfate is connected to a copper electrode immersed in 1 M copper II sulfate.

a) What are the relevant standard reduction potentials ?

Cu 2+ + 2 e - Cu 0.34 V

Zn 2+ + 2 e - Zn -0.76 V


Example Problem: produce a A zinc electrode immersed in 1 M zinc sulfate is connected to a copper electrode immersed in 1 M copper II sulfate.

a) What are the expected spontaneous oxidation half reaction,

reduction half reaction, and value of E  ?

oxidation: Zn  Zn 2+ + 2 e - 0.76 V

reduction: Cu 2+ + 2 e - Cu 0.34 V

E  = 1.10 V


Example Problem: produce a A zinc electrode immersed in 1 M zinc sulfate is connected to a copper electrode immersed in 1 M copper II sulfate.

a) What are the expected spontaneous oxidation half reaction,

reduction half reaction, and value of Ecell for a comparable

electrolytic cell?

The non-spontaneous reaction is the reverse reaction.

oxidation: Cu  Cu2+ + 2 e - - 0.34 V

reduction: Zn 2+ + 2 e - Zn - 0.76 V

Ecell - 1.10 V

Voltage applied to the electrolytic cell must exceed 1.10 V


Example Problem: produce a A zinc electrode immersed in 1 M zinc sulfate is connected to a copper electrode immersed in 1 M copper II sulfate.

a) Should the electrical current be applied to the zinc electrode

or the copper electrode to produce an electrolytic cell ?

Explain your answer.

Electrical current consists of electrons, and electrons must be

added to the desired cathode where reduction is to occur.

This is the zinc electrode.

oxidation: Cu  Cu2+ + 2 e -

reduction: Zn 2+ + 2 e - Zn


Example Problem 2: produce a Two platinum electrodes are immersed in a 1 M solution of silver nitrate. An electrical current is applied to the electrode on the left to produce an electrolytic cell.

a) What are the relevant standard reduction potentials ?

Since nitrate is stable, only two possible reactants can be

considered: Ag + and H2O. H2O has two possibilities

Ag + + e - Ag 0.80 V

2 H2O + 2 e - H2 + 2 OH - - 0.83 V

O2 + 4 H + + 2 e - 2 H2O 1.23 V


Example Problem 2: produce a Two platinum electrodes are immersed in a 1 M solution of silver nitrate. An electrical current is applied to the electrode on the left to produce an electrolytic cell.

b) What are the expected spontaneous oxidation half reaction,

reduction half reaction, and value of Ecell for the

electrolytic cell given the relevant standard reduction

potentials?

Ag + + e - Ag 0.80 V

2H2O + 2 e - H2 + 2 OH - - 0.83 V

O2 + 4 H + + 2 e - 2 H2O 1.23 V

The reduction of Ag + will occur since no Ag is present

for oxidation. H2O must therefore be oxidized.

reduction: Ag + + e - Ag 0.80 V

oxidation: 2 H2O  O2 + 4 H + + 2 e - - 1.23 V

Ecell = -.43 V


Example Problem 2: produce a Two platinum electrodes are immersed in a 1 M solution of silver nitrate. An electrical current is applied to the electrode on the left to produce an electrolytic cell.

c) How much voltage must be applied to produce silver

metal?

The voltage must exceed 2.03 V since the Ecell is – 2.03V

reduction: Ag + + e - Ag 0.80 V

oxidation: 2 H2O  O2 + 4 H + + 2 e - - 1.23 V

Ecell = -.43 V


Example Problem 2: produce a Two platinum electrodes are immersed in a 1 M solution of silver nitrate. An electrical current is applied to the electrode on the left to produce an electrolytic cell.

d) Will silver metal be deposited on the left electrode or the

right electrode? Explain your answer.

Left. The silver metal will be deposited on the cathode, the

electrode receiving the electrical current.


Example Problem 2: produce a Two platinum electrodes are immersed in a 1 M solution of silver nitrate. An electrical current is applied to the electrode on the left to produce an electrolytic cell.

e) What will be observed around the platinum electrode on the

right?

reduction: Ag + + e - Ag 0.80 V

oxidation: 2 H2O  O2 + 4 H + + 2 e - - 1.23 V

The right electrode is the anode where oxidation occurs. In

this reaction, oxygen gas is formed by oxidation of water so

bubbles of oxygen gas should be observed around the anode.


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