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Alcohol
Let’s Recall
Homologous Series
Functional Group
FormulaGeneral Formula
(m≥0, n≥1)Suffix Example
Alkane Alkyl RH
Alkene Alkenyl R2C=CR2
Let’s Recall
Homologous Series
Functional Group
FormulaGeneral Formula
(m≥0, n≥1)Suffix Example
Alkane Alkyl RH CnH2n+2 -ane Ethane
Alkene Alkenyl R2C=CR2 CnH2n -ene Ethene
Lesson objectives
1. Describe the alcohols as a homologous series containing the –OH group.
2. Draw the structures of alcohol, C1 to C5, and name the unbranched alcohols, methanol to butanol
3. Describe the properties of alcohols in terms of combustion and oxidation to carboxylic acids
4. Describe the formation of ethanol by the fermentation of glucose
Belong to a homologous series of organic compounds similar to alkanes and alkenes.
The hydrocarbon chains contain the functional group -OH (hydroxyl group)
What are Alcohols?
Structural Formula Chemical Formula
C2H5OH (molecular formula)
or
CH3CH2OH
(condensed structural formula)
=C C
H
H
H
H
H
H
OH
Naming the Alcohol
Methanol Total of one
carbon atom (meth-)
CH3OH
Ethanol Total of two
carbons atoms (eth-)
CH3CH2OH
Propanol Total of three
carbon atoms (propan-)
C2H5CH2OH
*Take note of the functional group’s location, highlighted by the dotted box
C H
H
H
H
C C
H
H
H
H
H
H
C C
H
H
H
H
C
H H
H
H
OH OH OH
Replace the ‘e’ with ‘anol’ at the end of the name of the hydrocarbon
Example:
Naming Alcohol
H H
H C C H
H H
ethane
H O
H C C O H
H
ethananol
H I
I H
No. of carbon atoms
Name of Alcohol Molecular Formula
Structural Formula Condensed Structural Formula
1 Methanol CH3OH CH3OH
2Ethanol C2H5OH
CH3CH2OH
3Propanol C3H7OH
CH3(CH2)CH2OH
4 Butanol C4H9OHCH3(CH2)2CH2OH
5 Pentanol C5H11OHCH3(CH2)3CH2OH
C H
H
H
H
C C
H
H
H
H
H
H
Naming the Alcohol
C C
H
H
H
H
C
H H
H
H
C C
H
H
H
H
C
H H
C
H
H
H
H
C C
H
H
H
H
C
H H
C
H
H
C
H
H
H
H
OH
OH
OH
OH
OH
The names of alcohol end with anol.
Alcohol are a homologous series with the general formula CnHn+1OH, where n is the number of carbon atoms in a molecule.
The simplest alcohol is methanol, with one carbon atom.
Naming the Alcohol
Physical Properties of ALcohols
Name Molecular formula Solubility In WaterState at r.t.p.*
(solid/liquid/gas)
Methanol CH3OH Very Soluble Liquid
Ethananol C2H5OH Soluble Liquid
Propananol C3H7OH Soluble Liquid
Butananol C4H9OH Slightly soluble Liquid
Alcohols are soluble in water
but their solubility decreases as their molecular size increases.
Unlike the alkanes and alkenes, the first four alcohols are liquid at room temperature and pressure.
Although alcohols contain the –OH group, they are not alkalis. In fact, they are all neutral.
Physical Properties ofAlcohols
Alcohols can take part in these
reactions: Combustion and Oxidation
Chemical Properties of Alcohols
Combustion
An alcohol burns in air to produce carbon dioxide and water vapour.
ethanol + oxygen → carbon dioxide + water vapour
C2H5OH + 3O2 → 2CO2 + 3H2O
C2H5OH + 3O2 → 2CO2 + 3H2O
Flame produced is clean
Combustion of alcohols are useful because: 1. Methanol is less likely than conventional fuel
to explode in an accident. It is a clean fuel.
2. When alcohol beverage is burnt with food, it gives a distinct flavour.
Combustion
We can oxidise an alcohol (for example, ethanol) by warming it with acidified potassium dichromate(VI).
Experimental setup:
Oxidation
(ethanol)
(ethanoic acid)
C2H5OH + acidified K2Cr2O7
CH3COOH
heat
coldwater
Chemical equation:
Oxidation
+ 2 [O] + H2O
Ethanol Ethanoic acid
The colour of potassium dichromate(VI) changes from orange to green.
Oxidation of alcohol is used in:
Breathalyzer to test the amount of alcohol consumed by drivers.
Oxidation
Formation of ethanol
Ethanol can be manufactured from:
1. hydration of ethene 2. fermentation of carbohydrates
Formation of ethanol- Hydration of ethene
Ethanol is manufactured by the catalytic addition of steam to ethene.
Conditions:
phosphoric(V) acid at 300 °C and 60 atm.
Phosphoric(V) acid (H3PO4) acts as a catalyst.
CH2 = CH2(g) + H2O(g) → CH3CH2OH (g)
Formation of ethanol-Fermentation of carbohydrates
Fermentation is a chemical process in which microorganisms such as yeast act on carbohydrates to produce ethanol and carbon dioxide.
Formation of ethanol-Fermentation of carbohydrates
Instructions:
• In your own groups of four, set up an experiment according to the experimental set up (A, B, C or D) which you can find on the last page of your worksheet.
• Each group will only be allocated to one of the four set ups.
Formation of ethanol-Fermentation of carbohydrates
Instructions:• Record your observations under the observations
column after one week and upload your observations onto the class blog according to your allocated set up.
• Your group is suppose to complete a series of questions pertaining to the experiment and hand in one set of answers per group two weeks later.
(You can find the questions on the class blog).
Uses of Ethanol?
solvents for paints, varnishes, perfumes
fuel for vehicles
alcoholic drinks
making ethanoic acid for preserving food and making
esters
ethanol
oxidation
Concept map construction
In your groups of four
•construct a concept map on the concepts that you have learnt today
•present your concept maps at the end of 5 minutes.
(Use the space in your worksheet to construct your concept map and make sure that it would be visible
on the visualiser).
How it all ties up