Explain the process of electrolysis and its uses Electrolysis A process where electrical energy is transformed into chemical energy It is not spontaneous electrical energy must be supplied for a ID: 538043
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Slide1
Electrolysis
Explain the process of electrolysis and its usesSlide2
Electrolysis
A process where electrical energy is transformed into chemical energy
It is not
spontaneous, electrical
energy must be supplied for a
reaction
to occur
It
has important applications such as
:
Electroplating
Extraction of reactive metals such as Na, Al from
metal ore
Industrial production of
NaOH
,
Cl
2
,H
2
Recharging
of car batteries & other rechargeable cells
Refining of copper metalsSlide3
The process occurring in an electrolytic cell
External Power Supply
Source of
electrons which can flow
.
(Current
is carried in solution by ions).Slide4
The process occurring in an electrolytic cell
Two electrodes immersed in a solution of
molten
reactant (Must be an
electrolyte
– solution that conducts electricity by a flow of
ions
)Slide5
The process occurring in an electrolytic cell
Anions
will flow in the same direction as the electrons.
They are attracted to the
Positive
anode
Anions
lose
electrons to become
oxidised
Slide6
The process occurring in an electrolytic cell
Cations
flow in the
opposite
direction
to electrons
They are attracted to the
negative
Cathode
Cations
gain electrons to become
reduced
Slide7
Electrolysis animation
G:\TGHS\Year 13 Chemistry\3.7 redox\Electrolysis.docxSlide8
Example – Electrolysis of water
Hoffman’s
Voltameter
is used for performing electrolysis of water and consists of platinum electrodes.
Water is a molecular compound. Pure or distilled water is a non-electrolyte (it contains no charged particles that can carry a current). Therefore, a few crystals of an ionic compound (like sodium chloride – to produce ions) or a few drops of a strong acid (hydrochloric acid, sulphuric acid – they completely dissociate into ions) need to be added to the water to make it become an electrolyte.
The anode and cathode are connected to a battery. The cell produces a small current of the order of a few milliamps and you will see bubbles appearing in the two arms of the
voltameter. The anode collects oxygen (the anion is attracted to the positive anode) and the cathode arm collects hydrogen gas (the cation is attracted to the negative cathode)Slide9Slide10
Extraction of aluminium
Aluminium ore is called bauxite. Bauxite contains aluminium oxide, water, iron oxide and other impurities. The purified dry ore, called alumina, is aluminium oxide - Al
2
O
3
.
The alumina must be molten for electrolysis to work, since the ions are not free to move in the solid state
solid state.
Slide11
Write equations for the reactions occurring…..
The steel container is coated with carbon
(graphite)
and this is used as the negative electrode (cathode).
Aluminium oxide (Al
2
O3) is an ionic compound. When it is melted the Al3+
and O
2-
ions are free to move and conduct electricity.
Electrolysis of the alumina/
cryolite
solution produces
aluminium at
the negative cathode and
oxygen
at the positive anode.Slide12