Chemical Properties of Alcohol

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Two methods of ethanol preparation:
a) Hydration of ethene, C2H4 with the presence of a

catalyst.
b) Fermentation of glucose or starch with the presence of

yeast.

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Ethene, C2H4 reacts with steam (H2O) at 300 °C and pressure of 60 atm,
with the presence of phosphoric acid, H3PO4 as a catalyst.

Hydration : 300C, 60 atm C2H5OH
C2H4 + H2O H3PO4
Ethanol
Ethene

HH HH

300 C, 60 atm,

H C C H + H2O H3PO4 HCC H

H OH

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Fermentation is the process in which yeast acts on carbohydrates (sugar
or starch) to produce ethanol, C2H5OH and carbon dioxide, CO2 in the
absence of oxygen, O2. (anaerobically)

C6H12O6  2C2H5OH + 2CO2

The ethanol, C2H5OH produced is purified
by fractional distillation.

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Procedure:
1. Put 20 g of glucose, C6H12O6 into 200 cm3 of distilled water into a conical flask.
2. Add 10 g of yeast into the conical flask and stir with a glass rod until the mixture

is even.
3. Close the conical flask with a stopper connected to the delivery tube.
4. Insert the end of the delivery tube into the test tube as shown in Figure 2.12.
5. Make sure the end of the delivery tube is dipped into the limewater.
6. Place the apparatus at room temperature (30 °C) for three days.
7. After three days, filter the mixture from the conical flask.

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8. The filtrate is poured into a round-bottom flask. The apparatus for distillation is set
up as shown in Figure 2.12.

9. Heat the filtrate in the water bath and collect the distillate at 78 °C.
10. Record the colour and smell of the distillate.

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Carbohydrate Observation
used
Foams were formed in the fermented
Glucose, mixture. A colourless gas that turned
C6H12O6 lime water milky was liberated. The
distillate was a colourless liquid with a
sharp smell.

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Discussion:
1. What is the function of yeast in the fermentation of glucose,

C6H12O6?
Yeast contains the enzyme zymase that acts as a catalyst, which
breaks glucose into ethanol and carbon dioxide.

2. Why must the end of the delivery tube be immersed in limewater?

To ensure that there was no oxygen gas from the surroundings
entering the conical flask containing the mixture undergoing
fermentation to prevent the ethanol produced from being oxidised
by oxygen gas to produce ethanoic acid which has a sour taste.

3. Name the gas released in the fermentation of glucose, C6H12O6.
Carbon dioxide

3. Name the product collected in fractional distillation at 78 °C.

Ethanol

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5. Explain why ethanol, C6H12O6 from the filtrate can be separated at 78 °C.
• The filtrate is a mixture of ethanol and water that have different
boiling points. The boiling point of ethanol is lower than that of
water.
• When the mixture is heated, ethanol boils first before water at
the temperature of 78 °C.
• The ethanol vapour formed at its boiling point will be
condensed in a Liebig condenser and then collected in a
beaker.

6. Write the chemical equation for the fermentation of glucose, C6H12O6

C6H12O6 yeast 2 C2H5OH + 2 CO2

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7. Fermentation to produce ethanol, C2H5OH can also be carried out using
fruits. Explain why.
Fruits contain carbohydrates, such as glucose, fructose and sucrose.
During fermentation, yeasts that contain the enzyme zymase break
down the molecules of these carbohydrates to produce ethanol.

Results:
1. Ethanol, C2H5OH can be prepared through the fermentation of

glucose, C6H12O6.
2. Ethanol, C2H5OH is a colourless and volatile liquid at room

temperature.

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• All alcohols have the same chemical properties due to the
presence of hydroxyl group, ― OH as a functional group.

• The important chemical reactions involving alcohols are:

Chemical reactions

Combustion Oxidation Dehydration

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• Alcohols burn in excess oxygen, O2 to produce carbon dioxide,
CO2 and water, H2O.

• Alcohols are flammable and burn with a blue flame without soot.

C2H5OH + 3O2  2 CO2 + 3 H2O

Combustion of alcohol releases a lot of heat and does not
pollute the environment. Thus, alcohol is a good fuel.
Ethanol, C2H5OH can be used as fuel for rockets.

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• Alcohols can be oxidised to form carboxylic acids, a homologous series
with functional group COOH in the presence of a suitable oxidising
agent.

• Common oxidising agents include acidified potassium manganate(VII),
KMnO4 solution and acidified potassium dichromate(VI), K2Cr2O7 solution.

C2H5OH + 2[O] CH3COOH + H2O

Ethanol Acidified K2Cr2O7 Ethanoic acid

H H / Acidified KMnO4 HO
H –C
C OH + 2[O] HKMnO4/ H+ – C C OH + H2O

HH H

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• Dehydration of alcohols involves the removal of a water molecule from
each alcohol molecule to produce a corresponding alkene.
Involves the removal of water.
Alcohol - H2O Alkene + H2O

Dehydration of ethanol

Porcelain pieces C2H4 + H2O

C2H5OH ethene
ethanol

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Involves the removal of water.
Alcohol - H2O Alkene + H2O

HH HH H +H OH
HCC
Porcelain pieces

H HCC

H OH Ethene

Hydroxyl group C2H5OH Porcelain pieces C2H4 + H2O
is removed
ethanol ethene
together with a
hydrogen atom
from an adjacent
carbon atom to

form H2O

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Alkenes, produced from the dehydration of alcohols have the
following characteristics:
1. Burn with yellow sooty flame,
2. Decolourise the brown colour of bromine water, Br2 to

colourless,
3. Decolourise the purple colour of potassium manganate(VII),

KMnO4 solution to colourless.

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Test on Distillate Observation

Colour change of potassium The orange acidified potassium dichromate(VI)
dichromate(VI),K2Cr2O7 solution solution changes to a green..

Colour change of potassium The purple colour of acidified potassium
manganate(VII),KMnO4 solution manganate(VII), KMnO4 solution is decolourised.

Colour of distillate Colourless liquid

Smell of distillate Vinegar smell

Effect on blue litmus paper It turned moist blue litmus paper red.

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1. Ethanoic acid
2. Acidified potassium dichromate(VI) solution /

Acidified potassium manganate (VII) solution
3. C2H5OH + 2[O] → CH3COOH + H2O
4. Acidic

Conclusion:
The oxidation of ethanol, C2H5OH produces ethanoic acid,
CH3COOH.

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Reagent Observation

Bromine water, Br2 The colourless gas produced decolourised the
reddish-brown bromine water

Acidified potassium The colourless gas produced decolourised the
manganate(VII),KMnO4 solution purple colour of acidified potassium
manganate(VII), KMnO4 solution.

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1. Ethene
2. As a catalyst.

Alumina (aluminium oxide)/ porous pot chips/ silica/
phosphoric acid can also be used to replace porcelain
chips.
3. C2H5OH → C2H4 + H2O

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+ H2O P: Dehydration
Q: Hydration
R: Oxidation

Conclusion:
The oxidation of ethanol, C2H5OH produces ethanoic acid,
CH3COOH.

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