Chemistry Reference
In-Depth Information
300
C, 60 atm
4
Which of the following organic chemicals are
alkanes or alkenes?
Propene, C
3
H
6
Butanol, C
4
H
9
OH
Octane, C
8
H
18
Nonane, C
9
H
20
Methanoic acid, HCOOH
Butene, C
4
H
8
State why you have chosen your answers.
ethene
steam
ethanol
phosphoric(
V
)
acid catalyst
C
2
H
4
(
g
)
H
2
O(
g
)
C
2
H
5
OH(
g
)
HH
CC
HH
HH
H
H
C
CH
OH
HOH
This reaction is reversible as is shown by the
equilibrium (
) sign. The conditions have been
chosen to ensure the highest possible yield of
ethanol. In other words, the conditions have been
chosen so that they favour the forward reaction.
For a further discussion of ethanol and alcohols
generally see p. 233.
L
Halogenation - a test for unsaturated
compounds
The addition reaction between bromine dissolved
in an organic solvent, or water, and alkenes is used
as a chemical test for the presence of a double bond
between two carbon atoms. When a few drops of this
bromine solution are shaken with the hydrocarbon,
if it is an alkene, such as ethene, a reaction takes
place in which bromine joins to the alkene double
bond. This results in the bromine solution losing
its red/brown colour. If an alkane, such as hexane,
is shaken with a bromine solution of this type, no
colour change takes place (Figure 14.13). This is
because there are no double bonds between the
carbon atoms of alkanes.
ethene
bromine
dibromoethane
C
2
H
4
(
g
)
Br
2
(in solution)
C
2
H
4
Br
2
(in solution)
HH
CC
HH
HH
Br
Br
HC
CH
Br Br
Questions
1
What is meant by the term 'addition reaction'?
2
Write a word and balanced chemical equation for the
reaction between ethene and hydrogen chloride.
3
Write the structural formula for pentene.
Figure 14.13
The alkene decolourises bromine in 1,1,1-trichloroethane.
