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