Chemistry Reference
In-Depth Information
Ethanol is by far the most important of the alcohols and
is often just called 'alcohol'. Ethanol can be produced
by fermentation (p. 236) as well as by the hydration of
ethene (Chapter 14, p. 224). It is a neutral, colourless,
volatile liquid which does not conduct electricity.
The more concentrated forms of alcoholic drinks
such as the spirits whiskey and brandy contain high
concentrations of ethanol. These are produced
by distillation after the fermentation is complete
(Chapter 2, p. 20).
Figure 15.5
Orange potassium dichromate(
vi
) slowly turns green as it
oxidises ethanol to ethanoic acid. Potassium manganate(
vii
) turns from
purple to colourless.
Combustion
Ethanol burns quite readily with a clean, hot fl ame.
ethanol + oxygen → carbon + water + energy
dioxide
CH
3
CH
2
OH(
l
) + 3O
2
(
g
) → 2CO
2
(
g
) + 3H
2
O(
g
) + energy
As methylated spirit, it is used in spirit (camping)
stoves. Methylated spirit is ethanol with small amounts
of poisonous substances added to stop people drinking
it. Some countries, like Brazil, already use ethanol
mixed with petrol as a fuel for cars (Chapter 6, p. 94)
and this use is increasing worldwide.
Cholesterol - a complex molecule
that contains the -OH group
Cholesterol is a naturally occurring and essential
chemical. It belongs to a family of chemicals
called steroids and also contains an alcohol group
(Figure 15.6). Cholesterol is found in almost all of
the tissues in the body, including nerve cells. Levels
of cholesterol above normal (above 6.5 mmol/l) are
associated with an increased risk of heart disease.
Cholesterol hardens and blocks off arteries by
building up layers of solid material (atheroma)
inside the arteries (Figure 15.7, p. 236). This is
particularly serious if the arteries that supply the
heart or brain are blocked. Simple tests are now
available to monitor cholesterol levels and people
with high levels can be treated and can follow
special low-fat and low-cholesterol diets.
Oxidation
Ethanol can be oxidised to ethanoic acid (an
organic acid also called acetic acid) by powerful
oxidising agents, such as warm acidifi ed potassium
dichromate(
vi
), or potassium manganate(
vii
).
During the reaction the orange colour of potassium
dichromate(
vi
) changes to a dark green (Figure 15.5)
as the ethanol is oxidised to ethanoic acid.
heat
ethanol
+
oxygen
(from
potassium
dichromate
(VI))
ethanoic
acid
+
water
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
2
OH(
l
)
2[O]
CH
3
COOH(
aq
)
H
2
O(
l
)
O
H
H
H
H
2
O
H
C
C
O
H
2[O]
H
C
C
C
HO
cholesterol
Figure 15.6
The structure of cholesterol.
O H
H
H
H
carboxylic acid group
Question
1
Write a word and balanced chemical equation for:
a
the combustion of butanol
b
the oxidation of butanol.
