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Electrolytic Cell and

Electroplating

Chapter 19 Page 776-781

Chem 12

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An electrolytic cellis a device in which

an external source of electrons (electrical

circuit) is used to make a non-

spontaneous redox reaction take place.

Molten (liquid) state of a pure substance is

the medium which the cell is made. Ex:

molten NaCl

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Oxidation at anode2Cl-Cl2+ 2e-

Reduction at

cathodeNa+ + 1e-Na

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NOTE:

The cathode is still under going reduction, but now

is negative.The anode is still under going oxidation, but now is

positive.

REASON: The electrodes are connected to a power source

that pump e- from negative to positive.

The electrode that is connected to the powersource is the cathode.

Since electrons are being forced into thecathode it becomes negative.

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An example of anelectrolytic cell iswhen molten NaCl is

electrolyzed to formliquid sodium andchlorine gas. Thesodium ions migrate

toward the cathode,where they arereduced to sodiummetal. Similarly,

chloride ions migrateto the anode and areoxided to formchlorine gas.

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E0net = E0ox+ E

0red

= (-1.36 V) + (-2.71 V)

= -4.07 V

The net cell voltage of -4.07

Because it is a non-spontaneous reaction the

E0netis always less than zero.

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In the electrolytic cells using molten ionic

compounds, the negative ions will be

oxidized.

The two electrodes used in an electrolytic

cell do not take part in any reaction. They

are non-reactive. Ex: carbon and platinum.

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Electroplating

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Electroplatingis a procedure that uses

electrolysis to apply a thin layer of a metal

over the surface of another metal.

Electrolysisis theprocess of making a

non-spontaneous chemical redox reaction

occur by passing electricity through a

substance. (electrolytic cell)

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In electroplating, the anode is made up of

the metal you want to coat the surface of

another metal with. There is also a salt solution present of the

anode metal.

While electrolysis is taking place, theanode metal is oxidized and goes into

solution as positive ions.

These positive ions are then reduced onthe surface of the cathode (the metal you

wish to coat).

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Examples of electroplating

Coating jewlery with

thin layer of

expensive metal.

Coating chromiumover steel to make

rust resistant.

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SAMPLE PROBLEM 1

A spoon is to be plated

with silver, Ag.1. Identify the anode

and cathode.

2. Write an equation forthe reaction takingplace at the anodeand at the cathodeand indicate whether

it is oxidation orreduction.

3. What electrolyte isused?

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ANSWER

1. Cathode = spoon (metal object to be coated),

Anode = silver electrode

2. As electrolysis takes place, the silver anode is

oxidized,Ag(s) Ag+(aq) + 1e-

The Ag+ (aq) ions in solution travel to the spoon

cathode and are reduced to form neutral Ag(s)on the surface of the spoon (cathode):

Ag+ (aq) + 1e- Ag(s)

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3. Electrolyte solution is made of AgNO3

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SAMPLE PROBLEM 2

A knife to be used as an eating utensil is to beplated with gold, Au.

a) Sketch and label a diagram of the apparatusused to electroplate the knife with gold.

b) Identify the anode and cathode.

c) Write an equation for the reaction taking place

at the anode and at the cathode and indicatewhether it is oxidation or reduction.

d) What electrolyte is used?