Download iGCSE chemistry Section 3 lesson 2

IGCSE CHEMISTRY
SECTION 3 LESSON 2
Content
The iGCSE
Chemistry
course
Section 1 Principles of Chemistry
Section 2 Chemistry of the Elements
Section 3 Organic Chemistry
Section 4 Physical Chemistry
Section 5 Chemistry in Society
Content
Section 3
Organic
Chemistry
a)
b)
c)
d)
Introduction
Alkanes
Alkenes
Ethanol
Lesson 2
c) Alkenes
d) Alcohols
c) Alkenes
3.6 recall that alkenes have the general formula CnH2n
3.7 draw displayed formulae for alkenes with up to four
carbon atoms in a molecule, and name the straight-chain
isomers (knowledge of cis- and transisomers is not
required)
3.8 describe the addition reaction of alkenes with
bromine, including the decolourising of bromine water as a
test for alkenes.
d) Ethanol
3.9 describe the manufacture of ethanol by passing
ethene and steam over a phosphoric acid catalyst at a
temperature of about 300°C and a pressure of about
60–70 atm
3.10 describe the manufacture of ethanol by the
fermentation of sugars, for example glucose, at a
temperature of about 30°C
3.11 evaluate the factors relevant to the choice of
method used in the manufacture of ethanol, for
example the relative availability of sugar cane and
crude oil
3.12 describe the dehydration of ethanol to ethene,
using aluminium oxide.
Organic Chemistry
It’s the chemistry of
carbon-containing
compounds
Hydrocarbon
= compound containing
hydrogen and carbon
only
The alkanes are
saturated hydrocarbons
– they form single
covalent bonds only
The alkanes have the
general formula of
CnH2n+2
Compounds exhibit
isomerism when they
have the same molecular
formula but different
structural formulae.
Alkenes
X
X
X
C
X
X
X
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
X
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
X
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
X
Ethane
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
X
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
H
H
C
C
H
H
X
Ethene
Alkenes
X
X
X
X
X
C
X
X
C
X
X
X
X
H
H
C
C
H
H
Double bond
X
Ethene
Alkenes
X
X
X
X
X
C
X
X
C
X
X
Alkenes are known as
unsaturated
hydrocarbons because
they contain a double
bond.
X
X
H
H
C
C
H
H
Double bond
X
Ethene
Alkenes
X
X
X
X
X
C
X
X
C
X
X
Alkenes are known as
unsaturated
hydrocarbons because
they contain a double
bond.
X
X
H
H
C
C
H
H
Double bond
X
Alkenes form a
homologous series
with the general
formula CnH2n
Alkenes
Name
n
Molecular
formula
Ethene
2
C2H4
Propene
3
C3H6
Butene
4
C4H8
Pentene
5
C5H10
Structural formula
Alkenes
Name
n
Molecular
formula
Ethene
2
C2H4
Propene
3
C3H6
Butene
4
C4H8
Pentene
5
C5H10
Structural formula
H
H
C C
H
H
Alkenes
Name
Ethene
n
2
Molecular
formula
C2H4
Propene
3
C3H6
Butene
4
C4H8
Pentene
5
C5H10
Structural formula
H
H
H
C C
H
C
H
C
H
H
H
C
H
H
Alkenes
Name
Ethene
n
2
Molecular
formula
C2H4
Propene
3
C3H6
Butene
4
C4H8
Pentene
5
C5H10
Structural formula
H
H
H
C C
H
C
H
C
H
H
H
C
H
H
Alkenes
Name
Ethene
n
2
Molecular
formula
C2H4
Propene
3
C3H6
Butene
4
C4H8
Pentene
5
C5H10
Structural formula
H
H
H
C C
H
C
H
C
H
H
H
C
H
H
Chemical properties of
alkenes
Chemical properties of
alkenes
1. Alkenes are generally more reactive than
alkanes.
Chemical properties of
alkenes
1. Alkenes are generally more reactive than
alkanes.
2. Ethene burns with a smoky flame. This is
because it contains a relatively high
percentage of carbon:
C2H4
+
3O2
 2CO2 + 2H2O
Other alkenes do not burn with a smoky flame
Chemical properties of
alkenes
3. Alkenes and unsaturated compounds undergo
addition reactions.
Chemical properties of
alkenes
3. Alkenes and unsaturated compounds undergo
addition reactions.
An addition
reaction is one in
which two
molecules combine
to form a single
molecule.
Chemical properties of
alkenes
3. Alkenes and unsaturated compounds undergo
addition reactions.
For example: alkenes react with bromine to
form 1,2-dibromoethane:
H
H
C
H
C
+
H
Br Br  H
H
H
C
C
Br Br
H
Chemical properties of
alkenes
3. Alkenes and unsaturated compounds undergo
addition reactions.
For example: alkenes react with bromine to
form 1,2-dibromoethane:
H
H
C
H
C
+
H
Br Br  H
H
H
C
C
Br Br
H
Ethanol
Ethanol
Ethanol belongs to the group of organic compounds
known as the alcohols.
Ethanol
Ethanol belongs to the group of organic compounds
known as the alcohols.
Alcohols contain the hydroxyl group, -OH
Ethanol
Ethanol belongs to the group of organic compounds
known as the alcohols.
Alcohols contain the hydroxyl group, -OH
The alcohols form a homologous series with the
general formula CnH2n+1OH
Ethanol
Ethanol belongs to the group of organic compounds
known as the alcohols.
Alcohols contain the hydroxyl group, -OH
The alcohols form a homologous series with the
general formula CnH2n+1OH
Eg. Ethanol C2H5OH
H
H
H
C
C
H
H
O
H
Manufacture of Ethanol
Manufacture of Ethanol
Ethanol may be produced in two ways:
1) Industrial preparation
Ethanol is made on a large scale by the hydration of
ethene at a temperature of 300oC and a pressure of
about 65 atmospheres.
Manufacture of Ethanol
Ethanol may be produced in two ways:
1) Industrial preparation
Ethanol is made on a large scale by the hydration of
ethene at a temperature of 300oC and a pressure of
about 65 atmospheres.
Manufacture of Ethanol
Ethanol may be produced in two ways:
1) Industrial preparation
Ethanol is made on a large scale by the hydration of
ethene at a temperature of 300oC and a pressure of
about 65 atmospheres.
C2H4 (g) + H2O(l)  C2H5OH(g)
Phosphoric acid is used as a catalyst.
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
Oil layer
Yeast in
glucose
solution
Lime
water
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
C6H12O6  2C2H5OH + 2CO2
sugar
Oil layer
Yeast in
glucose
solution
Lime
water
ethanol
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
C6H12O6  2C2H5OH + 2CO2
sugar
Oil layer
Yeast in
glucose
solution
Lime
water
ethanol
This process is known as
fermentation
Manufacture of Ethanol
Ethanol may be produced in two ways:
Fermentation is used in
2) Preparation by fermentation
wine and beer making.
The reaction is carried
Sugars are carbohydrates which can be broken down in
out
at ethanol
a temperature
the presence of yeast to
form
and carbonof
about 30oC.
dioxide.
Oil layer
Yeast in
glucose
solution
The reaction is known
C6anaerobic
H12O6  respiration
2C2H5OH + 2CO2
as
sugar
ethanol
as air must be
excluded.
This
process is known as
Lime
water
fermentation
Manufacture of Ethanol
Ethanol may be produced in two ways:
Fermentation is used in
2) Preparation by fermentation
wine and beer making.
The reaction is carried
Sugars are carbohydrates which can be broken down in
out
at ethanol
a temperature
the presence of yeast to
form
and carbonof
about 20oC.
dioxide.
Oil layer
Yeast in
glucose
solution
The reaction is known
C6anaerobic
H12O6  respiration
2C2H5OH + 2CO2
as
sugar
ethanol
as air must be
excluded.
This
process is known as
Lime
water
fermentation
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
C6H12O6  2C2H5OH + 2CO2
sugar
Oil layer
Yeast in
glucose
solution
Lime
water
ethanol
This process is known as
fermentation. The
reaction requires an
enzyme in yeast (zymase)
Manufacture of Ethanol
Ethanol may be produced in two ways:
2) Preparation by fermentation
Sugars are carbohydrates which can be broken down in
the presence of yeast to form ethanol and carbon
dioxide.
C6H12O6  2C2H5OH + 2CO2
sugar
Oil layer
Yeast in
glucose
solution
Lime
water
ethanol
The yeast eventually dies
when the alcohol content
reaches about 15% or
when the sugar is used up
Manufacture of Ethanol
Industrial
preparation
Which
method?
Preparation by
fermentation
Manufacture of Ethanol
Industrial
preparation
Which
method?
Depends upon the
relative availability of
the raw products.
Preparation by
fermentation
Manufacture of Ethanol
Industrial
preparation
Which
method?
In countries
where land is
scarce or not easy
to cultivate and
there are oil
reserves,
hydration of
ethene will be the
favoured process
Depends upon the
relative availability of
the raw products.
Preparation by
fermentation
Manufacture of Ethanol
Industrial
preparation
Which
method?
In countries
where land is
scarce or not easy
to cultivate and
there are oil
reserves,
hydration of
ethene will be the
favoured process
Preparation by
fermentation
In countries with no
crude oil reserves,
ethanol is more likely to
be made by the
fermentation method; in
particular if the climate
allows sugar cane to grow
well and there is plenty
of land available.
Depends upon the
relative availability of
the raw products.
Uses of Ethanol
Uses of Ethanol
Ethanol is used as
a solvent. Many
organic
compounds are
insoluble in water,
but soluble in
ethanol.
Uses of Ethanol
Ethanol is used as
a solvent. Many
organic
compounds are
insoluble in water,
but soluble in
ethanol.
Ethanol is used as a
fuel. In Brazil,
ethanol is produced by
the fermentation of
cane sugar, and then
added to petrol
(biofuel).
Uses of Ethanol
Ethanol is used as
a solvent. Many
organic
compounds are
insoluble in water,
but soluble in
ethanol.
Ethanol is used as a
fuel. In Brazil,
ethanol is produced by
the fermentation of
cane sugar, and then
added to petrol
(biofuel).
Ethanol is used in
the production of
wines, beers and
spirits.
Dehydration of Ethanol
Dehydration of Ethanol
A dehydration
reaction is defined as
a chemical reaction
that involves the loss
of water from the
reacting molecule.
Dehydration of Ethanol
Ethanol can be
dehydrated by
heating it in the
presence of a
catalyst, aluminium
oxide.
Dehydration of Ethanol
Delivery tube
Ethanol
soaked in
mineral
wool
Ethene gas
Aluminium
oxide
catalyst (or
porcelain
pieces)
Heat from
a Bunsen
burner
Water trough
Dehydration of Ethanol
Delivery tube
Ethanol
soaked in
mineral
wool
Ethanol  Ethene + Water
Ethene gas
C2H5OH  C2H4 + H2O
Aluminium
oxide
catalyst (or
porcelain
pieces)
Heat from
a Bunsen
burner
Water trough
End of Section 3 Lesson 2
In this lesson we have covered:
The Chemistry of Alkenes
Manufacture and reactions of Ethanol