(2019- Pattern)
Engineering Chemistry
Model Answer Set
Time: 03 hrs. Max. Marks: 70
3. Engineering Materials
1. What is the structural requirement for a polymer to show conductive property? Give
structure, doping and applications of polyacetylene? (7M)
Marking scheme- structural requirement - 2marks, structure -1mark, doping-2marks,
applications -2marks.
Answer-
Structural requirement-
If alternate double bonds are present in the polymer chain then the polymer conducts
electricity on its own. Such a system is called as conjugated system. (It should be noted that
out of these two bonds, one is a strong bond and the other is a weak µ bond.)
In these systems (polymers) there is overlapping of conjugated bonds over the entire
polymer chain. This leads to formation of conduction bond (CB) and valence bond (VB). If
the excitation of µ electrons present in the VB is done by either supplying heat or exposing to
light, then the polymer conducts electricity.
Structure –
(a) P-type Doping or Oxidative Doping:
A suitable oxidizing agent (e.g. halogen molecules) is added to conjugated polymer chains.
The oxidizing agent extracts a pair of electrons from chain and makes it a positively
charged cation.
Delocalization of positive charge (hole) takes place over the whole polymer chain and it
becomes conducting. e.g. polyacetylene + I2.
, (Delocalization of µ electrons to fill the ‘hole’)
This is called as oxidative doping because the polymer chain has actually lost the µ electrons
to halogen molecule.
(b) N-type Doping or Reductive Doping:
A suitable reducing agent (e.g. Alkali metal atoms like Na, K, Li) are added to conjugated
polymer chain which donate a pair of electrons to polymer chain. This makes the polymer
chain a negatively charged anion (i.e. electron rich) and it becomes conducting.
e.g.Polyacetylene + Na
(Delocalization of µ electrons to accommodate extra electrons)
Applications
In rechargeable light weight batteries
In telecommunication system.
In electronic devices such as transistors, diodes
,2 Give the structure, properties and applications of Polycarbonate
Marking scheme- structure - 1mark, properties -1mark, applications -1mark.
Structure-
Properties:
It is crystalline thermoplastic.
It shows very good mechanical properties like high impact strength, even at
low temperature.
It has low moisture absorption.
High heat resistance (140°C).
High thermal and oxidation stability in molten state.
It is transparent and self extinguishing.
Applications:
All types of housing or casing for electrical appliances, home appliances,
Computer peripherals.
Automobile head and tail light casing and lenses.
Telephone and cell phone casings.
Unbreakable crockery and glazing glass substitutes.
As a bulletproof material, helmets, covers of vehicle lights Also used for making CD and
DVD.
, 3. Define electroluminescence. Give the structure with mechanism and applications of
polyphenylenevinylene (PPV)
Marking scheme- Definition - 1mark, structure -1mark, mechanism -2mark.
Applications-1mark
Definition
The property in which a material produces bright light of different colours when stimulated
electronically is known as electroluminescence and the material which shows
electroluminescence is called as electroluminescent material.
(Structure of PPV or polyphenylene vinylene)
Mechanism-
Anode injects a hole towards a transport layer and then electrons injected by cathode layer
into the emitter layer. Then hole and electron recombine in the emitter layer causing emission
of light, during return of excited emitter to ground state.
Applications-
In photovoltaic cells
Electroluminescent night lamps
In flat panel displays
In light decoration.
Light strips for decorative buildings.
Engineering Chemistry
Model Answer Set
Time: 03 hrs. Max. Marks: 70
3. Engineering Materials
1. What is the structural requirement for a polymer to show conductive property? Give
structure, doping and applications of polyacetylene? (7M)
Marking scheme- structural requirement - 2marks, structure -1mark, doping-2marks,
applications -2marks.
Answer-
Structural requirement-
If alternate double bonds are present in the polymer chain then the polymer conducts
electricity on its own. Such a system is called as conjugated system. (It should be noted that
out of these two bonds, one is a strong bond and the other is a weak µ bond.)
In these systems (polymers) there is overlapping of conjugated bonds over the entire
polymer chain. This leads to formation of conduction bond (CB) and valence bond (VB). If
the excitation of µ electrons present in the VB is done by either supplying heat or exposing to
light, then the polymer conducts electricity.
Structure –
(a) P-type Doping or Oxidative Doping:
A suitable oxidizing agent (e.g. halogen molecules) is added to conjugated polymer chains.
The oxidizing agent extracts a pair of electrons from chain and makes it a positively
charged cation.
Delocalization of positive charge (hole) takes place over the whole polymer chain and it
becomes conducting. e.g. polyacetylene + I2.
, (Delocalization of µ electrons to fill the ‘hole’)
This is called as oxidative doping because the polymer chain has actually lost the µ electrons
to halogen molecule.
(b) N-type Doping or Reductive Doping:
A suitable reducing agent (e.g. Alkali metal atoms like Na, K, Li) are added to conjugated
polymer chain which donate a pair of electrons to polymer chain. This makes the polymer
chain a negatively charged anion (i.e. electron rich) and it becomes conducting.
e.g.Polyacetylene + Na
(Delocalization of µ electrons to accommodate extra electrons)
Applications
In rechargeable light weight batteries
In telecommunication system.
In electronic devices such as transistors, diodes
,2 Give the structure, properties and applications of Polycarbonate
Marking scheme- structure - 1mark, properties -1mark, applications -1mark.
Structure-
Properties:
It is crystalline thermoplastic.
It shows very good mechanical properties like high impact strength, even at
low temperature.
It has low moisture absorption.
High heat resistance (140°C).
High thermal and oxidation stability in molten state.
It is transparent and self extinguishing.
Applications:
All types of housing or casing for electrical appliances, home appliances,
Computer peripherals.
Automobile head and tail light casing and lenses.
Telephone and cell phone casings.
Unbreakable crockery and glazing glass substitutes.
As a bulletproof material, helmets, covers of vehicle lights Also used for making CD and
DVD.
, 3. Define electroluminescence. Give the structure with mechanism and applications of
polyphenylenevinylene (PPV)
Marking scheme- Definition - 1mark, structure -1mark, mechanism -2mark.
Applications-1mark
Definition
The property in which a material produces bright light of different colours when stimulated
electronically is known as electroluminescence and the material which shows
electroluminescence is called as electroluminescent material.
(Structure of PPV or polyphenylene vinylene)
Mechanism-
Anode injects a hole towards a transport layer and then electrons injected by cathode layer
into the emitter layer. Then hole and electron recombine in the emitter layer causing emission
of light, during return of excited emitter to ground state.
Applications-
In photovoltaic cells
Electroluminescent night lamps
In flat panel displays
In light decoration.
Light strips for decorative buildings.
