Chemical effect of electric
current
How things work
Atom
• All things around us are made up of atoms. Let us
recall the model of an atom. Every atom is made
up of positive and negative charged particles.
The flow of charged particle inside the
substance is called an electric current.
The materials, which allow electric current to
pass through them(in which charged particles
can move freely), are conductors. On the
other hand, materials, which do not allow
electric current to pass through them easily,
are insulators.
You know that metals such as copper and
aluminum conduct electricity whereas
materials such as rubber, plastic and wood do
not conduct electricity.
Electrical conductivity
• Electrical conductivity is a measure of how
well a material accommodates the movement
of an electric charge. Its SI derived unit is
the Siemens per meter.
• Good conductors have high electrical
conductivity than insulators.
Electrical conductivity of water
• Pure water is an insulator.
• Presence of small amount of impurities in
water makes water a conductor of electricity.
• Wet skin also becomes good conductor of
electricity. Be careful not to touch the
electrical appliances with wet hands.
Electrical conductivity of liquids
• Acid and bases dissolved in water are good
conductors of electricity.
• Molten salts are good conductors of electricity.
• But substances that exist as liquids in room
temperature like alcohols, oils are bad conductors of
electricity.
• The passage of electric currents through liquids
causes heating just as it does in solids.
Conductivity in solids and liquids
• In solids like metals which are good
conductors, the charge carriers are electrons.
• But in liquids the charge carriers are ions.(ions
are atoms or group of atoms with a positive or
negative charge)
Pure water does not conduct electricity because
it does not form enough iron to carry the
charge.
Recall…
• Ionic compounds can conduct electricity in
which states and why?
• Ionic compounds conduct electricity in molten
and aqueous states as the ions are not held in
their fixed positions and are free to move.
Solid ionic compounds
do not conduct
electricity as the ions
are held close
together in a lattice
and cannot move
freely.
Metals can conduct
electricity in solid
state due to the
‘sea’ of mobile
electrons.
Electrical conduction
Electrolytic conduction
by metals and graphite by electrolytes
Method of
conduction
Electricity is
conducted by the flow
of electrons from one
end of the conductor
to the other.
Electricity is conducted
by the movement of
positive ions and
negative ions across the
electrolyte.
Effect of
conduction
Metals and carbon
remain unchanged when
an electric current
flows through them.
The electrolytes are
decomposed to form new
substances when they
conduct electricity.
Electrolysis
• The passage of an electric current through a liquid
causes chemical changes. This process is known as
electrolysis.
• Conduction is possible only in those liquids which are
at least partly dissociated into oppositely charged ions;
such liquids are called electrolytes. (e.g. common salt,
sulphuric acid, etc.)
• +vely charged ions are called cation, and –vely charged
ion is called an anion.
• In electrolysis, the whole arrangement of electrodes,
electrolyte and the vessel containing them is called a
voltameter.
What is Electrolysis?
• Electrolysis is the conduction of electricity by
an ionic compound, when molten or dissolved
in water, leading to its decomposition.
• Hence, molten ionic compounds or aqueous
solutions containing free moving ions can
conduct electricity and are called electrolytes.
Terms to remember…
• Electrolytes:
– molten ionic compounds or aqueous solutions
• Electrodes: metal plates or carbon rods used
to conduct an electric current.
– Anode: electrode connected to the positive
terminal of the battery.
– Cathode: electrode connected to the negative
terminal of the battery.
• Anion: negative ion that is attracted to the
anode.
• Cation: positive ion that is attracted to the
cathode.
A Voltmeter
• Two electrodes:
– Cathode (negatively charged)
– Anode (positively charged)
• An Electrolyte
• External circuit
• Why is the anode positively charged and the
cathode negatively charged?
– The battery draws the electrons away from the
anode  positively charged.
– The battery supplies electrons to the cathode 
negatively charged.
What is Happening during Electrolysis?
• Electrical energy  chemical energy
• Ions are discharged at the cathode and anode.
– Cations receive electrons at the cathode.
– Anions give up electrons at the anode.
– The ions form atoms or molecules during the
process.
What Type of Reactions take place during
Electrolysis?
• At the cathode:
– Reduction takes place as cations gain electrons.
– Cu2+ + 2e-  Cu
• At the anode:
– Oxidation takes place as anions lose electrons.
– 2 Cl-  Cl2 + 2e-
• Hence, redox reactions take place during
electrolysis.
Electrolysis of molten NaCl
• Solid NaCl is heated strongly until it melts
(801°C).
• Molten NaCl contains Na+ ions and Cl- ions.
• At the cathode:
– Each Na+ ion gains an electron to form a sodium
atom.
– Na+ (l) + e-  Na (l)
• At the anode:
– Each Cl- ion gives up an e- to form a Cl atom. 2 Cl
atoms combine to form Cl2.
– 2 Cl- (l)  Cl2 (g) + 2 e-
• Overall reaction:
2 NaCl (l)  2 Na (l) + Cl2 (g)
• Na+ ions are discharged at the cathode and
Cl- ions are discharged at the anode.
Try this…
• Molten potassium chloride was electrolysed,
using carbon electrodes.
a) Write the formulas of the ions in the
electrolyte.
b) (i) Name the product at the cathode.
(ii) Write the half equation for the reaction at
the cathode.
c) (i) Name the product at the anode.
(ii) Write the half equation for the reaction at
the anode.
Industrial Applications of Electrolysis
1. Extraction of metals
– To extract very reactive metals from their ores.
2. Electrolytic refining
– To purify metals, such as copper
3. Electroplating
 The process of depositing a layer of metal on
another substance using electrolysis.
What is electroplating?
• Electroplating (often just called "plating") is
the deposition of a metal coating onto an
object or metal using electrolysis.