10 std electroyysis

1. CHAPTER – 5
ELECTROLYSIS

2. Electro = Electricity
Lysis = Separating or Splitting into
Definition:
It is defined as the decomposition of a chemical
compound (electrolyte) in the aqueous or molten
state by the passage of direct current resulting in
discharge of ions as neutral atoms at their
respective electrodes.
Eg: NaCl → Na1+ + Cl1-
At Cathode: Na1+ + 1e- →Na (reduction)
At Anode : Cl1- - 1e- →Cl (Oxidation)
Electrolysis involves both Oxidation and reduction,
So it is a redox reaction.

4. INTRODUCTION
Electrolyte Non Electrolyte
Chemical compound that
allows the electricity in
the fused or aq. State ,
undergo decomposition.
Electrolytes are Ionic
compounds.
Particles : Ions only or
Ions and molecules only
Chemical Compound that
do not allow the
electricity in fused or aq.
State, do not undergo
decomposition.
Non- electrolytes are
covalent compounds.
Particles : Molecules only.

5. STRONG ELECTROLYTE WEAK ELECTROLYTE
Allow large amount of
electricity to pass
through them, Good
conductors of electricity.
Almost completely
dissociated in fused or
aq.state.
Particles: Ions only.
Eg: Strong Acids, bases.
Allow small amount of
electricity to pass
through them, poor
conductors of electricity.
Partially dissociated in
fused or Aq. State.
Particles: Ions and
Unionised molecules.
Eg: Weak Acids, Bases.

6. ANODE CATHODE
Positive terminal.
Anions migrate towards
anode.
Ions lose electron in
anode to be neutralised,
so oxidation takes place.
So called as oxidising
electrode.
Cl -1 - 1e-1 → Cl
Negative terminal.
Cations migrate towards
cathode.
Ions gain electron from
cathode to neutralise, so
reduction takes place.
So called as Reducing
electrode.
Na1+ + 1e- → Na

7. ANIONS CATIONS
Negative charge.
Migrate towards Anode.
They donate or lose
electrons.
Oxidation process.
Positive charge.
Migrate towards Cathode.
They Accept or gain
electrons.
Reduction process.

8. ELECROLYTIC CELL : A non-conducting vessel
containing the electrolyte.
ELECTRODE – Allows or leave the electric current .
Anode – positive terminal,
Cathode – Negative terminal.
IONS – Anion – Negative ion,
Cation – positive ion.
ELECTROLYTE - Chemical compound
(Aq/fused).
Requirements for Electrolysis

9. ELECTROLYSIS

10. An electrolyte dissolve in water, dissociates into
free cations and anions.
Degree of dissociation : the extent to which the
electrolyte gets dissociated into ions.
The amount of electricity conducted by
electrolyte depends upon the concentration of
ions in the solution.
No. Of positive charges is equal to No. of
negative charges. (electrolytic equilibrium)
Postulates of Arrhenius Theory of
electrolysis

11. The passage of electricity through an electrolyte
cause metallic ions to migrate towards cathode and
non-metallic ions towards anode.
The preferential discharge of ions depends on its
position in the electrochemical series.
No. of electrons gained by anode is equal to no. of
electros donated by the cathode.
The products of electrolysis are formed at anode
and cathode itself. Since exchange takes place on
the surface of the electrodes.
Hydrogen gas and metals are liberated at cathode
and hence called electropositive elements.
Non-metals are liberated at the anode and are called
electronegative elements.
CHARECTERISTICS OF ELECTROLYSIS

13. Electrolytic Dissociation Ionisation
It is a process takes
place in Electrovalent or
ionic compounds.
It involves separation of
ions, of the ions which
are already present as
ionic compound.
It is a process takes
place in covalent
compounds.
It involves the formation
of charged ions from the
molecules which are not
in ionic state.

14. Solid Sodium chloride is a non- electrolyte, While
molten or Aq. NaCl is an electrolyte - Give reason?
Because of
Strong Electrostatic Force of attraction.
Electrolytic dissociation of ionic
compounds NaCl

15. 


In Solid State:
Ions are held together with strong electrostatic
force of attraction, So the ions are not free to
move.
For the conduction of electricity we need freely
moving ions.
So when we heat an solid ionic compound, it
gains some energy and break the bond, then move
freely hence becoming a good conductor of
electricity.

16. 


In Aqueous state:
Water(H2O)has slight positively charged
hydrogen as well as negatively charged oxygen
atoms.
So when an electrolyte (NaCl) is dissolved in water,
positive charge(Na+), of the electrolyte gets
attracted by negatively charged oxygen atom,
negative charge(Cl-) of the electrolyte is attracted
by positive charged hydrogen atom.
Thus positive and negative ions will become free
to move in the solution.

18. 




Polar covalent compounds are non-electrolytes in the
gaseous state, but ionize in aqueous state.
In gaseous state:
HCl in gaseous state is unionized and does not
conduct electricity.
In aqueous state:
HCl has slight positively charged hydrogen and
negatively charged chlorine atoms.
Water(H2 O) also have slight +ve charged hydrogen
and –ve charged oxygen.
When HCl is added to H2 O, +vely charged hydrogen is
pulled by –vely charged oxygen and H+ ions combines
with water forming H3 O+ ions, leaving the residual
Chloride ions.
IONIZATION OF COVALENT COMPOUNDS (HCl)

20. METAL (Cu)
(Metallic conduction)
ELECTROLYTE (CuSO4 )
(Electrolytic Conduction)
Flow of electricity takes
place by flow of electrons.
No decomposition of
parental metal, thus
chemical properties are
not changed.
Good conductors of
electricity in solid and
molten state.
No transfer of matter, so
no new products are
formed.
Flow of electricity takes
place by flow of ions.
Decomposition of parental
metal, thus chemical
properties are changed.
Good conductors of
electricity in aqueous or
molten state.
Transfer of ions takes
place, so new products
are formed.

21. Give reason :
Copper metal is a good conductor of electricity,
but it is a non- electrolyte, while copper sulphate
solution is an electrolyte?

22. Reason:
Copper metal is a good conductor of electricity, but
it is a non- electrolyte, since it does not undergo
chemical decomposition on passage of electric
current.
Copper sulphate solution is an electrolyte, because
it decomposes to form copper and sulphate ions
on passage of electricity.

23. An experiment to determine whether the given
compound ( Acid/base/salt) in aqueous/fused
state is a
STRONG /WEAK ELECTROLYTE

24. Non electrolyte Strong
electrolyte
Weak
electrolyte

26. Depending on the ease with which the metals
lose their electrons and form ions- they are
arranged in a series known as-
METAL ACTIVITY SERIES or
ELECTROCHEMICAL SERIES
ARRANGEMENT:
The elements are arranged in the way that
Ionize most readily(with difficulty)- Top of the
series Ionize easily - lower end of the series.
ELECTROCHEMICAL SERIES

28. 

At the top of the series:
Metals which ionize most readily – are included
at the top of the series.
Metal loss electrons and become positive ions.
(K – 1e- →K1+ )
Positive ions discharged at the cathode with
most difficulty.
Cations gains electron with great difficulty to
become neutral atom.
(K1+ + 1e- → K) [reduction reaction]

29. 

At the lower end of the series:
Metals which ionize least readily are at the lower
end of the series.
Metals lose electron with great difficulty to
become positive ions.
( Cu – 2e- → Cu2+) [oxidation]
Positive ions discharged at cathode most readily.
Cations gains electron most easily to become
neutral atoms.
( Cu2+ + 2e- →Cu)

30. The preferential discharge of ions is also known as
selective discharge of ions.
Factors Affecting selective discharge of ions:
Relative position of cation or anion – in
electrochemical series.
Concentration of the ions – in the electrolyte
Nature of the electrode – active / inert.
Selective discharge / Preferential discharge
of ions

31. Discharge of cations and anions at the respective
electrodes:
In Aqueous solution:
Dissociation of electrolyte:
Ions migrate towards cathode:
Na+ , H+ --- (H+)
Ions migrate towards anode:
Cl- , OH- --- (OH-)
Relative position of cation / anion – in
electrochemical series
NaCl → Na+ + Cl-
H2 O → H+ + OH-

33. Concentrated solution of NaCl:
Dissociation of electrolytes:
NaCl → Na+ + Cl-
H2 O → H+ + OH-
Ions migrating towards cathode:
Na+ , H+ --- (Na+)
Ions migrating towards anode:
Cl- , OH- --- (Cl-)
Concentration of the ions in the
electrolyte

34. 1. Particles present in electrolytes are ________.
2. Completely dissociated electrolytes are____.
(Strong/Weak/Non Electrolytes)
3.Anode is connected towards the ____ end of the battery.
4.The device in which the electrolysis is carried out is _______.
5._______ is the reducing electrode.
6._______ are positively charged ions.
7. Hydrogen gas is liberated at _______.(Anode/Cathode)
8.Ionisation takes place in ________ compounds.(Ionic/Covalent)
9.Give reason why solid NaCl is a non-electrolyte?
10. When HCl is dissolved in water, what is the resultant product
formed?
11.Copper metal is a non electrolyte though it is a good
conductor, but copper sulphate is an electrolyte- give reason.
12.Weak electrolytes are ______ dissociated.
Questions

35. 

Inert and active electrodes:
Inert electrodes: Do not take part in electrolytic
reaction. - Iron, Graphite, Platinum.
Active electrodes: take part in electrolytic
reaction. – Copper, Nickel, Silver.
Nature of the electrode

36. AQUEOUS CuSO4 SOLUTION
Active electrode - Copper Inert electrode - Platinum
CuSO ↔ Cu + SO
HO ↔ H + OH
Electrodes:
Cathode: Copper
Anode : Copper
Reaction at anode:
Cu – 2e → Cu
Cu Participate in the
reaction and does not
allow OH ion to be
discharged.
Product at anode: Cu
ions
Reaction at cathode:
Cu + 2e → Cu
CuSO4 ↔ Cu2+ + SO4
2-
H2O ↔ H1+ + OH-
Electrodes:
Cathode: Copper
Anode: Platinum
Reaction at anode:
OH1- - 1e- →OH * 2
[2OH →H2O +[O] ]
4OH →2H2O + O2
Reaction at cathode:
Cu2+ + 2e- → Cu

37. 1.
Find out the answers:
Explain how electrolysis is an example of redox
reaction?
2.Give reason : An aqueous solution of NaCl
conducts electricity.
3.(2020) Question paper.
Difference between
i) Conductor and electrolyte
ii) Cations and anions
Home Work

38. 1. If the given compound is a strong electrolyte the bulb
_____
(Glows brightly/ dim/ do not glow)
2. HNO3 Dissociates into ______.
3.Metals in the lower end of the series ionize ____ ( Most
readily/ Easily).
4. Metals are highly _______.
5.Cathode is a electron (donar/acceptor).
6.Depending upon the concentration of the electrolyte, in
Conc. CuSO4 solution, which gets attracted towards
cathode ____.
7.An example of active electrode ____ ( Nickel/iron/
Graphite).
Self Evaluation

39. 1.
2.
Electrolysis of Molten/fused Lead bromide.
Electrolysis of Acidified Water using
(Platinum electrode).
3. Electrolysis of Aqueous Copper Sulphate using
(Copper electrode).
Examples of electrolysis

41. Requirements :
Electrolytic cell : Silica crucible
Electrolyte : Molten / fused lead bromide
Electrode :Cathode: Iron/Graphite
Anode : Graphite
Temperature :380°C
Current :3Amperes
Electrode reaction:
PbBr2 ↔ Pb2+ + 2Br1-
Ions Present : Pb2+ , Br1-
1.Electrolysis of Molten Lead Bromide(PbBr2)

42. Reaction at Cathode:
Pb2+ + 2e- → Pb
Pb2+ ions are
discharged at cathode-
as neutral lead atoms
by accepting electrons.
Product at Cathode:
Lead Metal(Silvery grey)
(reduction)
Reaction at Anode:
Br1- - 1e- → Br
Br + Br → Br2
Br1- ions are discharged at
anode as neutral
bromine atoms by loss
of electrons.
Bromine atoms combine
to form a molecule of
bromine.
Product at anode:
Bromine vapour (
Reddish brown fumes)
(Oxidation )
Cathode and Anode reactions

43. I. Electrolytic cell : made up of silica crucible and it is
heated from outside.
1. Silica crucible is used in the electrolysis of Lead bromide
– Why?
Because it is non reactive, withstand high temperature and
non conductor of electricity.
2. Solid lead bromide is a non conductor of electricity- Why?
Because its ions are not free but held together by strong
electrostatic force of attraction.
3.Why the silica crucible is to be heated?
Because to maintain the lead bromide in the Molten state.
Give reasons ???? Pg No 113

44. II. Reactions at cathode and anode:
1.Cathode is a electron donor, lead ions need
electrons to be neutralized into metallic lead.
Pb2+ + 2e- → Pb
2. Neutral bromine atoms combine to form bromine
molecules.
Br1- - 1e- → Br
Br + Br → Br2
Reddish brown vapours of bromine are evolved at
anode.

45. III Electrode:
Inert electrodes are used because, they should not
take part in the reaction, otherwise they would
prevent the discharge of the respective ions.
2020 Question:
Give reason- Why Graphite anode is preferred to
other inert electrodes like platinum?
Because Graphite anode is unaffected by the
reactive bromine vapours.

46. 1.Explain the following:
A solution of sugarcane does not conduct
electricity, but a solution of NaCl is a good
conductor.
2. Electrons are added to an element ‘Y’. Which
electrode will Y migrate during electrolysis?
3.A,B,C different electrolytic cells. Cell A contains
NaCl solution, the bulb glows brightly, cell B
contains acetic acid, the bulb glows dimly, cell
C contains sugar solution, the bulb does not
glow. Give reasons for each observation.
HOME WORK

47. 1. what product is formed at anode in the electrolysis
of Aq. Solution of CuSO4 , using inert platinum
electrode?
2. Name the electrode used in the electrolysis of lead
bromide.
3. Name the product formed at anode during the
electrolysis of lead bromide.
4.Why silica crucible is used in the electrolysis of lead
bromide?
5. Solid lead bromide is a non electrolyte – Why?
6. Why graphite anode is preferred to other inert
electrodes like platinum?
7.State one appropriate observation: Electricity is
passed through molten lead bromide.
Self Evaluation

48. Requirements:
Electrolytic cell: Glass vessel as shown
Electrolyte : Acidified water (H2SO4 )
Electrode : Cathode, Anode: Pt Foil – inert electrode
Temperature : Ordinary temperature
Current : 3 Amperes
Electrode reaction :
H2 SO4 ↔ 2H1+ + SO4
2-
H2O ↔ H1+ + OH-
Ions present: H1+ , SO4
2- , OH-
2. Electrolysis of acidified water – using platinum
electrodes

50. Cathode and Anode reactions
At Cathode: (H1+) At Anode: (SO4
2- , OH- )
H1+ + 1e- → H * 4
2H + 2H → 2H2
H+ Ions are discharged at
cathode and neutralized
into H atoms.
As H atoms are unstable,
combines with another H
atom to form H2.
(Hydrogen gas)
Product at cathode :
Hydrogen gas (H2) – 2
volumes
OH1- - 1e → OH * 4
4OH → 2H2O + O2
Among the two anions OH-
ion gets discharged at
anode.
Unstable OH atoms
combines to form water
and oxygen.
Product at Anode:
Oxygen gas (O2) – 1 volume

51. 1. Why pure water is a non electrolyte?
It has very low concentration of ions, so it
cannot be dissociated. So it will be in the form
of molecules, hence it do not conduct
electricity.
2. Why Acidified water is considered as an
example of catalysis reaction?
Pure water is an non electrolyte and it cannot be
dissociated. It can be decomposed by adding
sulphuric acid, which doesn’t take part in a
reaction but makes the water as a good
conductor of electricity.
Give reason Pg No 115

52. 3. Why current is passed for a prolonged period
of time ?
The products of the electrolysis are hydrogen
and oxygen gas, which have different solubility
in the electrolyte. Thus the current is passed for
prolonged time before the collection of gas to
have accurate comparison between the amount
of products formed. This ensures the saturation
of gases.
4. Why Dil. Sulphuric acid is preferred to dil.
Nitric acid?
Nitric acid is a volatile acid, may decompose
and nitrate radical may tends to intrefere with the
electrolytic reaction.

53. 5. The ratio of hydrogen and oxygen liberated at cathode
and anode is 2: 1 by volume.
At Cathode:
H1+ + 1e- → H * 4
2H + 2H → 2H2
At Anode:
OH1- - 1e → OH * 4
4OH → 2H2O + O2
2H2O → 2H2 + O2
6. Remember that, Total concentration of Sulphuric acid
molecules remains the same , Since it is the H+ ions and
OH- ions which are actually discharged at anode and
cathode.

54. Dissociation of Alkalis:
Aqueous solution of NaOH – using inert electrodes
NaOH ↔ Na1+ + OH1-
H2O ↔ H1+ + OH1-
At Cathode:
H1+ + 1e- → H * 4
2H + 2H → 2H2 Product : Hydrogen gas
At Anode:
OH1- - 1e → OH * 4
4OH → 2H2O + O2 Product: Oxygen gas

55. 1.State what is observed when copper sulphate solution
is electrolysed using a Platinum anode?
2. An electrode A is connected to the positive terminal of
the battery and B is connected to the negative terminal.
i) Give the names of the electrode A and B
ii) Which electrode is a oxidizing electrode?
3. When Dil. NaCl is electrolysed using graphite
electrodes, the cations that is discharged at the
cathode most readily is ___(Na+, OH-, H+, Cl-)
4. Electrolysis of molten lead bromide is considered to be
redox reaction – Why?
5.Electrical conductivity of acetic acid is less than
compared to that of dil H2SO4 at given concentration.
HOME WORK

56. 1.Name the gas released at cathode when acidulated
water is electrolysed.
2. Correct the following statement: Lead Bromide conducts
electricity.
3. Give reason- Why electrolysis of acidified water is an
example of catalysis?
4.The Acid that is dehydrating as well as drying agent is
_____.
5. Electrode used in the electrolysis of acidified water is
_____.
6.Total concentration of sulphuric acid in the electrolyte
_____( Increases/decreases/remains same)
7.The volume of hydrogen and oxygen gas are in the ratio
of _____.
8. Name the compound during electrolysis in its molten
Self Evaluation -3

57. Requirements:
Electrolytic cell: Glass vessel as shown
Electrolyte : Aq. Copper sulphate solution
Electrode : Cathode, Anode: Copper (Active
electrode)
Temperature : Ordinary temperature
Current : 3 Amperes
Electrode reaction:
CuSO4 ↔ Cu2+ + SO4
2-
H2O ↔ H1+ + OH-
Ions present : Cu2+ , H1+ , SO4
2- , OH-
Electrolysis of Aq. CuSO4 – using
copper electrode

59. Electrode reaction:
CuSO4 ↔ Cu2+ + SO4
2-
H2O ↔ H1+ + OH-
Reaction at cathode: ( Reduction)
Cu2+ + 2e- → Cu
Product at cathode: Copper metal
Reaction at anode: (Oxidation)
Cu – 2e- → Cu2+
Cu Participate in the reaction and does not allow OH
ion to be discharged.
Product at anode: Cu2+ ions (Nil)

60. AQUEOUS CuSO4 SOLUTION
Active electrode - Copper Inert electrode - Platinum
CuSO ↔ Cu + SO
HO ↔ H + OH
Electrodes:
Cathode: Copper
Anode : Copper
Reaction at anode:
Cu – 2e → Cu
Cu Participate in the reaction
and does not allow OH ion to
be discharged.
Anode diminishes in Mass
Product at anode: Cu ions
Reaction at cathode:
Cu + 2e → Cu
CuSO4 ↔ Cu2+ + SO4
2-
H2O ↔ H1+ + OH-
Electrodes:
Cathode: Copper/ Platinum
Anode: Platinum
Reaction at anode:
OH1- - 1e- →OH * 2
[2OH →H2O +[O] ]
4OH →2H2O + O2
Reaction at cathode:
Cu2+ + 2e- → Cu

61. 1. The electrolyte aqueous copper sulphate may be acidified
with traces of dilute sulphuric acid.
It enhances the conductivity of the electrolyte and may prevent
hydrolysis of the electrolyte.
2. Blue color of Aq. Solution of CuSO4 solution remains
unchanged during electrolysis of Aq.CuSO4- using copper
electrodes but fades away when platinum electrodes are
used.
If Copper anode is used, for every Cu ions gets discharged at
cathode, a copper ion is added to the solution at the anode.
Hence No. of Cu ions remains the same.
If Platinum anode is used the Cu ions discharged at the
cathode are not replaced at the anode. So the color fades
away.

62. 1. State the observations at the anode and cathode
during electrolysis of
i) Molten lead bromide using graphite electrodes.
ii) copper sulphate using Cu electrodes.
2. Blue colour of aqueous solution of CuSO4 turns
almost colourless on its electrolysis using Pt
electrodes.- Give reason.
3. Pure water a Non electrolyte becomes an electrolyte
on addition of H2SO4 – Give reason.
4. Give the electrode reaction for the formation of
Hydrogen and oxygen (2:1) from the electrolysis of
acidified water using Pt electrodes.
HOME WORK

63. 1. ____ Lead bromide does not conduct electricity.
2. The solution of substance that conducts
electricity is called _____.
3. An electrically charged atom is called ____.
4. Pure water almost consists entirely of _____.
5.During ionisation metals lose electrons, this
change can be called as _____.( Oxidation/
reduction)
6.Electrolytic deposition of a superior metal on a
baser metal is called as _____.
7.The acid used in electrolysis of water is ____.
8.Conductivity of metals due to ______.
Self evaluation 4

64. 


The Main applications of electrolysis are:
Electro plating of Metals.
Electro- refining or purification of metals.
Electrometallurgy – Process of extraction of
metals by electrolysis.
Applications of electrolysis

65. DEFINITION:
It is the electrolytic process of deposition of a
superior metal on the surface of a baser metal or
article.
Reasons for electroplating :
1. Prevents corrosion or rusting – of the base
metal. Eg: Base metal iron plated with Ni/Cr.
2.Makes the article attractive and gives it an
expensive appearance.
Eg: A brass article plated with Silver/Gold.
Electroplating of Metals

66. Condition:
1.The article to be
electroplated is always
placed at the cathode.
2. The metal to be plated
on the article is always
made the anode. It has
to be replaced
periodically.
Reason:
1.During the reaction,
the metal is always
deposited at the
cathode by gain of
electrons.
2. The metal anode
continuously dissolves-
as ions in solution and
hence replaced
periodically.
Conditions – For Electroplating

67. Condition:
3. The electrolyte must
contains ions of the
metal used for plating
on the article.
4. A low Current and for
a longer time should be
used.
5. A direct current and
not A.C current should
be used.
Reason:
3.The electrolyte dissociates
into into ions of the metal
which migrate towards the
cathode and deposited as
neutral metallic atoms on
the cathode.
4. Higher current causes
uneven deposition of the
metal. Low current for a
longer time- initiates a
smooth, firm, uniform and
long lasting deposition.
5. A.C. current causes
discharge and ionization to
alternate at the cathode-
thus giving no effective
coating.

68. i)
1.State on what basis Acids ,bases and salts
classified as strong/ weak electrolytes.
2.’ Iron is electroplated with silver’.
Define the underlined term.
ii) State 2 reasons for electroplating.
3. Name the electrolyte used for electroplating the
article with silver.
4.Draw the diagram for electroplating an article
with silver.
HOME WORK

69. 1 The vessel in which electrolysis of lead bromide
carried out is ____.
2. _____ is the electrolyte used in the process of
Nickel plating.
3. Why articles are electroplated?
4.Define electroplating.
5. What is electrometallurgy?
Self evaluation - 5

70. 1. Electroplating with – Nickel
Electrolyte: Aq. Solution of NiSO4 ( Nickel
Sulphate)
Nature of electrode:
Cathode: Clean article to be electroplated
Anode : Active electrode ( Block of pure Ni
Metal)
Electrode reactions:
NiSO4 ↔ Ni2+ + SO4
2-
H2 O ↔ H1+ + OH1-
Electroplating of metals

71. Reactions at cathode and anode
At Cathode: At Anode:
Ni2+ + 2e- → Ni (deposited)
Ni ions accept the
electrons from cathode
and neutralise into Ni
metal and gets deposited
at the article.
Ni - 2e- → Ni2+ (Cations)
Anions migrate towards
anode, but here we are
using active electrode.
Ni anode loses the electron
to give Ni2+ ions.
Hence Anode diminishes in
mass.
Product at Anode: Nil

72. Electrolyte: Aq. Solution of Sodium silver
Cyanide – Na[Ag(CN)2] or Sodium
Argentocyanide.
Why we are not using AgNO3 as an electrolyte? –
Give reason.
Because Ag1+ ions from above complex salt
solution is slow compared to that from AgNO3.
Hence even deposition of silver is obtained on the
article.
Preparation: AgCN + NaCN → Na[Ag(CN)2]
2. Electroplating with Silver

73. Nature of the electrode :
Cathode: Cleaned article to be electroplated
Anode : Active electrode ( Plate/Block of Ag
metal)
Electrode reactions:
Na[Ag(CN)2] ↔Na1+ + Ag1+ + 2CN1-
H2O ↔ H1+ + OH1-

74. Reaction at Cathode:
Ag1+ + 1e- → Ag (Deposited)
Ag1+ ions move towards the cathode and
discharged as neutral Ag atoms – by gain of
electrons.
Thus silver is deposited on the article.
Reaction at Anode:
Ag – 1e- → Ag1+
The anions do not discharged at anode because we
are using active electrode.
Anode diminishes in mass
Product at Anode: NIL
Reactions at Anode and Cathode

75. Anode diminishes in Mass

76. 1.Write two application of electrolysis, in which the
anode diminishes in mass.
2. Mr. Ramu wants to electroplate his keychain with
Ni to prevent rusting. For this electroplating.
i) Name the electrolyte.
ii) Name the cathode.
iii) Name the anode.
iv) Give the reaction at cathode.
v) Give the reaction at anode.
HOME WORK - 5

77. 1. On electrolysis Ag+ and H+ ions migrate towards ____
(cathode/anode) and ____ (Ag+ / H+ ) are discharged.
2. Electrolysis is an ____ reaction in which reduction
reaction takes place at ____ ( anode/cathode).
3.During silver plating of an article using potassium argento
cyanide as an electrolyte, the anode material should be
_____.( Cu, Ag, Pt, Fe).
4. Rewrite the statement with correct missing word:
Cations migrate during electolysis.
5. In electroplating an article with silver, the electrolyte
sodium argentocyanide is preferred over silver nitrate-
Give reason.
Self Evaluation - 6

78. Definition:
It is a process by which metals containing
impurities are purified electrolytically to give a
pure metal.
Refining means to make pure.
Electro – the method employed to make the metal
pure (ie) Electrolysis.
Electro refining – of metals
(Purification)

79. Electrolyte: Aq. Copper sulphate solution
Nature of the electrode:
Cathode : Pure thin sheet of copper
Anode : Impure Block of copper
Electrode Reaction:
CuSO4 ↔ Cu2+ + SO4
2-
H2O ↔ H1+ + OH-
Reaction at cathode: Cu2+ + 2e- → Cu
Reaction at anode : Cu – 2e- → Cu2+
Hence Anode diminishes in mass.
Electro-refining of Copper

81. The Impure block of Cu anode gets used up and the
impurities settle down.
The pure Cu metals dissolves out from Cu anode
and Cu ions are formed in solution at the anode
are deposited at the cathode. (pure sheet).
The impurities present in Cu anode gets settle
down as anode mud/ Slime, which contains
insoluble impurities like Gold/Silver.
Impurities like iron, Zinc etc ionize and dissolve in
the electrolyte (CuSO4).

82. Metals generally refined by electrolysis:
Metals which are extracted by electrolysis.
(ie) Highly electropositive metals are already
deposited at the cathode in pure state and hence
need not to be refined further.
Zinc, Lead, Copper, Mercury and Silver are generally
refined by electrolysis.

84. Definition:
The process of extraction of metals by electrolysis.
Method of extraction of metals depends on the
position of electrochemical series.
ELECTROMETALLURGY

86. 1. Electrolysis – K, Na, Ca, Mg, Al
Their oxides are highly stable.
Metal has strong affinity for oxygen.
On electrolysis metal is deposited at the cathode.
Metals generally extracted by electrolysis are K,
Na, Ca, Mg, Al.
Ways of extraction

87. Examples:
i) Electrolyte: Fused NaCl.
NaCl ↔ Na1+ + Cl 1-
Cathode: Na1+ + 1e- →Na
Anode: Cl1- - 1e- → Cl
Cl + Cl → Cl2
ii) Electrolyte : Fused CaCl2
CaCl2 ↔ Ca2+ + 2Cl-
Cathode: Ca2+ + 2e- → Ca
Anode : 2Cl1- – 2e- → 2Cl (Cl2)

88. iii) Electrolyte : Fused Alumina
Al2 O3 ↔ 2Al3+ + 3O2-
Cathode: 2Al3+ + 6e- → 2Al
Anode: 3O2- – 6e- → 3[O]
3[O] + 3[O] → 3O2
Alumina is a highly stable oxide and Al have
strong affinity for oxygen hence it cannot be
reduced using reducing agent ( C, CO, H2).

89. 



2. By using Reducing agents : C, CO, H2.
Their oxides are less stable.
They reduce metallic oxides to metal.
Example:
CuO + C Δ→ Cu + CO
Zn, Fe, Pb, [H], Cu these metals are extracted by using
reducing agents.
3. By Thermal decomposition: Hg, Ag
Their oxides are least stable.
Heat alone can reduce metallic to metal.
Example:
2HgO Δ→ 2Hg + O2

90. 1.
i)
Explain the term Electrometallurgy. At which
electrode is the extracted metal is always
deposited.
2. During purification of copper. State
Anode used ii) Electrolyte used iii) Write the
equation taking place at anode.
3. The article to be electroplated is always kept at
Cathode – give reason.
HOME WORK - 6

91. 1. Electrolysis is the passage of ____ through a liquid or
solution accompanied by a ____ change.
2. An electrolyte is a _____.
3. Water is a _____.
4. We can expect that pure water ___ conduct electricity.
5. Ionization is a ____ process.
6. _____ Lead bromide does not conduct electricity.
7. With platinum electrodes, hydrogen gas is liberated at
____ and Oxygen at ____.
8. The metallic electrode that doesn’t takes part in the
electrolytic reaction is ___ ( Cu/Ag/Pt/Ni).
9. Electrolyte used in the electroplating of i) Nickel ii) Silver.
10. A Suitable cathode used in the electrorefining of
copper is ______.
DISCUSSION

92. 11. The electrode that increases in mass during the
electro refining of silver.
12. Cathode are connected to the ____ end of the battery.
13.Electrolysis is an example of ___ reaction.
14. According to Arrhenius theory, the amount of
electricity depends on the _____ of the ions.
15.Electrolytes are good conductors in _____ state.
16. Electrolytic dissociation takes place in ____
compounds.
17. In electrolysis of molten lead bromide, the product at
cathode is _____.
18. In electrolysis of acidified water, oxygen gas is
formed at _____.
19. An Article to be electroplated is always kept at _____.
20. In electro refining, impure metal is kept at ______.

93. 21. In electro refining , the impurities are settle down
at ______.
22. Extraction of metals by the process of electrolysis
is called as ____.
23. Zn, Fe, Pb are extracted by _______.
24. Metals are always deposited at ______.
25. Formic acid dissociates into _____.
26. Copper is a ____ electrode.
27. Non – metals are liberated at _____.
28. In electrolysis of copper sulphate using copper
electrode, Product at anode is ____.
29. Thermal dissociation is decomposition of the
compound by ________.
30. Extraction of metals depend upon the _______.

94. 1. Solid NaCl does not conduct electricity, while molten/
Aq. NaCl conducts electricity – Why?
2. What happens in ionization, while HCl is added to water?
3. Though Cu metal is a good conductor, it is a non –
electrolyte, while CuSO4 is an electrolyte- Why?
4. In electrolysis of lead bromide, the reaction is carried out
in silica crucible- why?
5. A graphite anode is preferred to other inert electrode like
platinum – Why?
6.Pure water is a non electrolyte – Why?
7. Electrolysis of acidified water is an example of catalysis
reaction – Why?
Give reason:

95. 8. Why Dilute Suphuric acid is preferred than nitric
acid?
9. The ratio of hydrogen and oxygen are 2:1 volume –
Why?
10. While using Pt electrode the colour of the solution
fades away- Why?
11. What are the reasons for electroplating?
12. A low current for a longer period of time is used –
Why?
13. DC current and not alternating current is used why?
14. Electrolysis is an example of redox reaction – Why?

96. 1. Electrolysis. 103
2. Electrolytic cell. 104
3. Electrodes and ions 104
4. Postulates of arrhenius theory. 105
5. Electrochemical / Activity series. 110
6.Preferential /Selective discharge of ions.
7.Inert and active electrodes with eg. 113
8. Electroplating 118.
9. Electro refining 120.
10. Electrometallurgy and activity series. 121.
Define the following

97. 1.Electrolyte and Non- electrolyte. 103
2. Strong and weak electrolyte 103.
3. Anode and Cathode 104.
4. Anion and cation 104.
5. Electrolytic dissociation and ionization 105.
6. Metal and electrolyte 107.
Differentiate between :