3D_Electrolytic and Chemical Cells

7/30/2019 3D_Electrolytic and Chemical Cells

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(D) Electrolytic

andChemical Cell


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Learning Objectives:

You should be able to: Explain with examples the oxidation and reduction

reactions at the electrodes of various chemical cells.

Explain with examples the oxidation and reductionreactions at the electrodes of various electrolytic cells.

State the differences between electrolytic and chemicalcells in terms of basic structure, energy conversion andthe transfer of electrons at the electrodes.

Compare and contrast electrolytic and chemical cells

with reference to the oxidation and reduction processes. Appreciate chemical cells as a source of renewable

energy.


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Comparison of Electrolytic Cell and Chemical Cell

Electrolytic Cell Chemical Cell


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requires a source of electric

current

(uses E Energy)

does not requires a source of

electric current

(releases E Energy)

electrode may be of the

same material eg Carbon

electrode must be of two

different metals

electrical energy

chemical energy

chemical energy

electrical energy

electron flow from thepositive electrode(anode) to

the negative electrode

(cathode)

electrons flow from themore electropositive metal

(negative terminal) to the

less electropositive

metal(positive terminal)


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Oxidation & Reduction in Electrolytic Cells

Electrolysis of Molten lead (II) bromide, PbBr2


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Electrolysis of Molten lead (II) bromide, PbBr2Anode Cathode

Br lose e to become Br2(g) Pb2+ gain e to become Pb(s)

2Br(l) Br2(g) + 2e(1) ( 0 )

Pb2+(l) + 2e Pb(s)

(+2) ( 0 )

Br are oxidized to Br2

(Oxidation)

Pb2+ are reduced to Pb

(Reduction)

Br acts as reducing agent Pb2+ acts as oxidizing agent

Electrons transfer from reducing agent to oxidizing agent


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Electrolysis of Potassium Iodide solution, KI


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Electrolysis of Potassium Iodide solution, KI

Anode Cathode

I lose e to become I2(aq) H+ gain e to become H2 (g)

2I

(aq) I2(aq) + 2e(1) ( 0 )

2H+(aq) + 2e H2(g)

(+1) ( 0 )

I are oxidized to I2

(Oxidation)

H+ are reduced to H2

(Reduction)

I acts as reducing agent H+ acts as oxidizing agent

Electrons transfer from reducing agent to oxidizing agent


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Oxidation & Reduction in Chemical Cells

Zinc stripCopper strip

Anode Cathode

Zinc act as negative

terminal

Copper acts as positive

terminal

Oxidation Half-equation:

Zn(s) Zn(aq) + 2e

Reduction Half-equation

Cu2+(aq) + 2e Cu(s)


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For both Electrolytic and Chemical Cells

The electrode at which oxidation occurs is

called the anode.

The electrode at which reduction occurs is

called the cathode.


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in terms of Redox Reaction

SimilaritiesIn both cells,

electrons are transferred from the reducing agent to the oxidizing

agent

oxidation occurs at the anode

reduction occurs at the cathode


Differences

oxidation occurs at + electrode anode = + electrode

reduction occurs at + electrode cathode = + electrode

reduction occurs at electrode

cathode = electrode

oxidation occurs at electrode

anode = electrode


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Others Chemical Cells

There are 2 types of cells

Primary cell ----- not rechargeable

dry cell , Alkaline cell, Mercury cell

Secondary cell ----- rechargeable

nickel-cadmium cell, lead-acid accumulator

nickel metal hydride cell, lithium ion cell,

lithium polymer cell


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Practice D1. An electrolysis process of copper(II) sulphate solution

using carbon electrode has been carried out.a. State the observation obtained at

electrode A and B.

b. Write the half equation thatoccurred at each electrode

c. Determine the processes thathappened at each electrode

d. Name the

a. Oxidizing agent

b. Reducing agent

e. What is the changes of theoxidation number of copper?

f. What could be observed at theelectrodes if the experiment isrepeated using 1.0 moldm-3sodium chloride solution?


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Dry Cells ----- not rechargeable


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Alkaline Cells --- not rechargeable


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Nickel-cadmium cells ---

rechargeable


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Lead-acid accumulator ---

rechargeable


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Lithium Ion Cell( Li-ion)


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Lithium Polymer Cell (Li-Poly)


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Nickel Metal Hydride Cell (NiMH)

3D_Electrolytic and Chemical Cells

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