After completing this topic you should be able to :
•
Write the balanced formula equation for the fermentation reaction.
•
State that ethanol is a member of a homologous series called the alkanols.
•
Identify an alkanol from the hydroxyl group and the ‘-ol’ name ending.
•
Name straight-chain alkanols, incorporating the position of the hydroxyl group,
from shortened and full structural formulae (only C1 to C8)
•
Give examples of the uses of alcohols.
•
State when an alkanol undergoes a mild oxidation reaction the product is an
alkanoic acid.
Common alcohol is called ethanol.
H H
H
C C O H
C2H5OH
H H
CH3CH2OH
hydroxyl
group
The – O-H group of atoms is called the HYDROXYL GROUP. This is called the
functional group as it gives the molecule the chemical properties of an alcohol.
The name ethanol tells you the following information.
eth – contains 2
carbon atoms
ethanol
ol – contains a
hydroxyl group
(–OH)
an – contains
single C – C bond
Ethanol is a member of a family of alcohols called ALKANOLS.
Ethanol is a flammable liquid, which burns to produce
and
.
The table below shows further properties of ethanol.
PROPERTY TESTED
OBSERVATION
Appearance (colour and state)
Colourless liquid
Ethanol is a covalent
liquid. It is neutral and
soluble in water.
Smell
Mild smell
Ethanol is a good solvent.
Conductivity
Insulator
Solubilty in water
Soluble
pH (acidic / neutral / alkaline?)
Neutral
Ethanol has a structure
similar to water. This is
why it is soluble in water.
Solvent action:
ink
Soluble
varnish
Soluble
chlorophyll in leaves
Soluble
H atom in H2O atom
substituted with an
ethyl group (C2H5-).
Ethanol is made in the alcoholic drinks industry by fermentation of sugars (glucose)
using enzymes in yeast.
enzymes in
yeast
glucose
enzymes in
yeast
C6H12O6
ethanol
(alcohol)
+
carbon
dioxide
2 C2H5OH
+
2 CO2
Ethanol (industrial alcohol) is made in the petrochemical industry by adding water
(steam) across the C=C bond in ethene. This reaction is called HYDRATION.
ethene
H
H
+
C C
H
H
C2H4
ethanol
+
O
H
H
H
H O
H
C C
H
H H
+
C2H5
Ethanol is the second member of the homologous series of alcohols called
ALKANOLS.
methanol
ethanol
H
H H
H
C
O
H
CH3OH
H
H
C C O H
H H
C2H5OH
The general formula of the alkanol family is
propanol
H H H
H
C C C O H
H H H
C3H7OH
CnH2n + 1OH
No. of
C atoms
Alkanol
Name
Molecular
Formula
Full Structural Formula
Shortened Structural Formula
H
1
methano
l
CH3OH
H
C
O
H
H
CH3OH
H H
2
ethanol
C2H5OH
H
C C O H
H H
CH3CH2OH
H H H
3
propanol
C3H7OH
H
C C C O H
H H H
CH3CH2CH2OH
4
butanol
C4H9OH
H
H H H
H
C C C
C
H H H
H
O H
CH3CH2CH2CH2OH
The following graph shows the boiling point of alkanols versus number of carbon
atoms.
140
C4H9OH
Boiling point / oC
120
C3H7OH
100
C2H5OH
80
CH3OH
60
40
20
0
4
2
3
1
No. of carbon atoms
As the number of carbon
atoms in the alkanol
molecule increases, the
boiling point increases.
The alkanols have similar
chemical properties and
have a general formula
showing they are a
HOMOLOGOUS SERIES.
Alkanol molecules form isomers; therefore the name has to describe the structure.
The naming rules learned for hydrocarbons apply except the molecule name ends
in – OL.
H
H O H
H H H
H
3
2
1
C C C O H
H H H
propan - 1 - ol
1
2
3
H H H
4
2
C C C
C
H H H
H
H
H
propan - 2 - ol
H
H
C C C
H
H
3
H
C
1
O
H
H
H
3 - methylbutan - 1 - ol
Alcoholic drinks.
Fuel for vehicles.
Solvent for varnish, perfume,
deodorant.
Feedstock for making chemicals.
Mixed with ethanol to make methylated
spirits.
Fuel
Feedstock for making chemicals.
Medical – used in hand sanitizers and
drug preparation.
Fuel
Feedstock for making chemicals.