3. Alcohol -

Alcohol
HOMOLOGOUS SERIES
By: Ms Siti Soleha

What we are learning today?

◦Alcohol nomenclature
◦Preparation of alcohol
◦Chemical properties of alcohol

Short recap

What is homologous series?



The alcohols are the family of organic
compounds that contain the -OH
group.

The hydroxyl group OH is different from the hydroxide ion
(OH‒ ) in alkali. There are no hydroxide ions (OH‒) in alcohol

Naming of straight chain alcohol according to the
IUPAC nomenclature:

i. Determine the number of carbon atoms in the longest carbon chain containing
the hydroxyl group -OH to derive the name of the alkane containing the same
number of carbon atoms as alcohol.

ii. Replace the “e” ending from the alkane name with “ol”. Example:



The first 4 members of Alcohol

Number of carbon Name of alcohol Molecular Structural formula
atom formula

CnH 2n+1OH

1

2

3

4





Preparation method of alcohol

❖ Ethanol, C2H5OH is the most important alcohol and has
many uses.

❖ It is a good solvent. It dissolves many substances that do
not dissolve in water.

❖ It evaporates easily – it is volatile. That makes it a suitable
solvent to use in glues, printing inks, perfumes, and
aftershave.

❖Two methods for preparation of ethanol:

(a) Fermentation of glucose or starch with the presence of
yeast

(b) Hydration of ethene, C2H4 with the presence of a catalyst

Fermentation of Glucose

❖ Ethanol is made from glucose using yeast, in the absence of air:
❖ Yeast is a mass of living cells. The enzymes in it catalyse the reaction.
❖ The process is called fermentation, and it is exothermic.
❖ Ethanol can be made in this way from any substance that contains sugar, starch, or cellulose.

(These break down to glucose.) For example it can be made from sugarcane, maize,
potatoes, and wood.
❖ The yeast stops working when the % of ethanol reaches a certain level, or if the mixture gets
too warm.
❖ The ethanol is separated from the final mixture by fractional distillation.(purification)

Aim: To prepare ethanol, C2H5OH through fermentation of glucose.

Steps:

1. Put 20 g of glucose, C6 H12O6 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.Make sure the end of the delivery tube is

dipped into the limewater.
5. Place the apparatus at room temperature (30 °C) for three days.
6. After three days, filter the mixture from the conical flask..
7. The filtrate is poured into a round-bottom flask. The apparatus for distillation is set up as shown

in Figure 2.12.
8. Heat the filtrate in the water bath and collect the distillate at 78 °C.
9. Record the colour and smell of the distillate

Fermentation of Glucose

Fractionating
column

https://www.youtube.com/watch?v=eYgBBRlVOLI

Hydration of Ethene

❖ Hydration means water is added on. This is an addition reaction.
❖ The reaction is reversible, and exothermic.
❖ High pressure and a low temperature would give the best yield. But in practice the reaction

is carried out at 570°C, to give a decent rate of reaction.
❖ A catalyst is also used, to speed up the reaction.

Ethanol as a Fuel

❖ Ethanol burns well in oxygen, giving out plenty of
heat:

C2H5OH (l) + 3O2 ( g) → 2CO2 ( g) + 3H2O (l) + heat

❖It is increasingly used as a fuel for car engines
because:

1. it can be made quite cheaply from waste plant
material

2. many countries have no petroleum of their own,
and have to buy it from other countries; it costs a
lot, so ethanol is an attractive option

3. ethanol has less impact on carbon dioxide levels
than fossil fuels do

Ethanol and Global Warming

❖Like the fossil fuels, ethanol does produce
carbon dioxide when it burns.

❖This is a greenhouse gas, linked to global
warming. But ethanol has less impact on carbon
dioxide levels in the atmosphere, because …

Combustion
Oxidation
Dehydration

◦ Alcohol burns in excess oxygen, O2 to produce carbon dioxide, CO2 and water, H2O.
◦ Alcohol is flammable and burns with a blue flame without soot.

◦ The combustion of ethanol, C2H5OH releases large quantities of heat.

◦ Ethanol, C2H5OH can be used as fuel for rockets. • Alkanes, alkenes and alcohols
burn completely in oxygen,
producing carbon dioxide gas and
water.

• Perform the same steps as alkanes
and alkenes to balance the
equation for the combustion of
alcohol

◦ Alcohol 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.

◦ The purple colour of acidified potassium manganate(VII), KMnO4 solution is decolourised in
this reaction.

◦ The orange colour of acidified potassium dichromate(VI), K2Cr2O7 solution turns green when
it reacts with ethanol. In this reaction, ethanol is also oxidised into ethanoic acid.

Experiment!

Steps:

1. Pour 5 cm3 of potassium dichromate(VI), K2Cr2O7 solution into a
boiling tube.

2. Add 10 drops of concentrated sulphuric acid, H2SO4.
3. Gently heat the solution.

4. Add 3 cm3 of ethanol, C2H5OH drop by drop into the boiling tube.
5. Connect the delivery tube to the boiling tube as shown in the

diagram.

6. Heat the mixture with a gentle flame until the mixture boils.

7. Collect the distillate in a test tube and test it with the blue litmus
paper.

8. Repeat steps 1 to 6 by replacing potassium dichromate(VI),
K2Cr2O7 solution with potassium manganate(VII), KMnO4 solution.

A: Oxidation of Ethanol by acidified Experiment!
potassium dichromate(VI) solution.
B: Oxidation of Ethanol by acidified
potassium manganate(VII) solution.

https://www.youtube.com/watch?v=1r1Z3xjIiJQ https://www.youtube.com/watch?v=d7pCdCg84_E&t=42s

Observation!

Test on distillate Observation

Colour change of potassium
dichromate(VI), K2Cr2O7 solution
Colour change of potassium
manganate(VII), KMnO4 solution
Colour of distillate

Smell of distillate

Effect on blue litmus paper

Discussion!

❖What is the product formed by the oxidation reaction of ethanol, C2H5OH?
❖Name the oxidising agent used in this experiment.
❖Write the chemical equation of the reaction that occurs.
❖What is the property of the product of alcohol oxidation?

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

Example

◦ (b) Oxidation of propanol, C3H7OH

◦ Dehydration of alcohol involves the removal of a water molecule from each alcohol molecule
to produce a corresponding alkene.

◦ Water molecules are removed from the alcohol when alcohol vapour is flowed over
a strongly heated catalyst, such as porcelain chips, aluminum oxide, alumina or
concentrated sulphuric acid.

◦ Chemical equation:

◦.

Experiment!

Steps:
1. Place the glass wool in a boiling tube.
2. Pour 2 cm3 of ethanol, C2H5OH into the boiling tube to wet the

glass wool.
3. Place the porcelain chips in the middle of the boiling tube.
4. Heat the porcelain chips with a strong flame. Heat the glass

wool with a gentle flame to vaporise the ethanol, C2H5OH and
the vapour is flowed through the heated porcelain chips.
5. Collect two test tubes of the gas released.
6. (i) Add a few drops of bromine water, Br2 into the first test tube
and shake.
(ii) Add a few drops of acidified potassium manganate(VII ),

KMnO4 solution into the second test tube and shake

Experiment!

Reagent Observation

Bromine water, Br2
Potassium manganate(VII),
KMnO4 solution

https://www.youtube.com/watch?v=sF-VOucVOmI

Discussion!

❖ Name the gas released when ethanol, C2H5OH undergoes dehydration.
❖ State the function of porcelain chips.
❖ Write the chemical equation for the dehydration of alcohol, C2H5OH

Conclusion: Dehydration of ethanol,
C2H5OH produces ethene, C2H4 .

Example (b)
Dehydration of Propanol, C3H7OH

◦ Alkene, produced from the dehydration of alcohol, has the following characteristics:

burns with decolourises
yellow the brown
sooty colour of
flame, bromine
wcaotleoru, rBler2ssto,

decolourises the purple
colour of potassium

msoanlugtiaonnatteo(VcoII)lo, KurMlensOs.4

Chemical Properties of other Members of the Alcohol
Homologous Series

◦ All members of the alcohol homologous series have the functional group
hydroxyl -OH, which is similar to ethanol, C2H5OH.

◦ Thus, other members of the homologous series also undergo combustion,
oxidation and dehydration

Try yourself!

To be continued…