ALCOHOLS,
CARBOXYLIC
ACIDS AND
ESTERS
Objective
identify alcohols, acids and esters by their functional groups.
relate the properties of alcohols, acids and to their functional
groups.
describe the reactions of ethanol.
describe the fermentation process by which ethanol is
produced from carbohydrates.
describe the reactions of ethanoic acid.
explain hydrolysis of esters including saponification.
compare soapy and soapless detergents
Alcohols, also known as alkanols, form a homologous
series with the general formula CnH2n+1OH
They are organic compounds that have OH hydroxyl
group as their functional group.
Suffix: 'anol'
The first two alcohols in the homologous series does not
show structural isomerism.
Alcohols with three or more carbon atoms show
structural isomerism by branching and changing the
position of the functional group.
When naming the isomers of alcohols,
number the carbon atoms in the longest chain from the
end closest to the functional group and indicate the
position of the hydroxyl group in the name.
All the same rules applies as we have learnt before.
Polar molecule is a covalent molecule in which one part
has a slightly negative charge and the other part of the
molecule has a slightly positive charge.
Alcohols are molecules polar due to the presence of the
polar -OH groups.
The volatility and solubility of alcohols are related to the
polar nature of the molecule.
Alcohols are less volatile than their corresponding
alkanes with the same amount of carbon atoms.
This means that they have higher boiling point.
Why is this so?
Alcohols are less volatile than their corresponding
alkanes with the same amount of carbon atoms because
the polar -OH causes the forces of attraction between
the alcohol molecules to be stronger than the non polar
molecules. As a result alcohols are either liquid or solid
at room temperature.
The boiling point of alcohols increases as the number of
carbon atoms in the molecules increases. This is because
the intermolecular forces between the molecules
increases as the size increases.
Polar solutes dissolve in polar solvents.
Water is a polar solvent hence alcohols are soluble in
water.
The small alcohols are completely soluble in water
however solubility decreases as the number of carbon
atoms increases.
Due to the presence of the hydroxyl group,
alcohols undergo a variety of reactions. The
strength of the reactions decreases as the
number of carbon atoms in the molecule
increases.
Ethanol burns easily in air or oxygen to produce carbon dioxide
and water. This is an exothermic reaction.
Complete combustion occurs
Ethanol burns with a clear blue flame because the ratio of the
carbon to hydrogen atoms is low. All the carbon is converted
to carbon dioxide and no unreacted carbon remains to produce
soot.
Ethanol reacts with sodium to produce sodium ethoxide.
When a piece of sodium metal is dropped in ethanol steady
effervescence occurs as the hydrogen gas is evolved and a
colourless solution of sodium ethoxide in alcohol is formed.
When ethanol is mixed with concentrated sulfuric acid and the
mixture is heated to 170 oC, the ethanol is dehydrated to
ethene.
A water molecule is removed from the ethanol molecule, the
hydroxyl group from one carbon atom and hydrogen from the
other carbon atom.
This results in the formation of a C=C.
When ethanol is heated with a powerful oxidising agent such
as acidified potassium manganate (VII) solution or acidified
potassium dichromate (VI) solution, the ethanol is oxidised to
ethanoic acid.
The breatherlyzer test
Production of ethanol by fermentation
Winemaking
Rum Manufacture
Carboxylic acids , also known as alkanoic, form a
homologous series with the general formula CnH2n+1COOH
They are organic compounds that have COOH carboxyl
group as their functional group.
Suffix: 'anoic acid'
It important to remember that the functional group of
carboxylic acids has one more carbon atom which must
be taken into consideration when naming the carboxylic
acids.
Example
CH3COOH -Ethanoic Acid
Carboxylic acids are molecules polar due to the presence
of the polar -OH part of the carboxyl functional group.
The volatility and solubility of carboxylic acids are
related to the polar nature of the molecule.
Carboxylic acids are less volatile than their
corresponding alkanes with the same amount of carbon
atoms.
This means that they have higher boiling point.
Why is this so?
Carboxylic are less volatile than their corresponding
alkanes with the same amount of carbon atoms because
the polar -OH causes the forces of attraction between
the carboxylic molecules to be stronger than the non
polar molecules. As a result carboxylic acids are either
liquid or solid at room temperature.
The boiling point of carboxylic acids increases as the
number of carbon atoms in the molecules increases.
This is because the intermolecular forces between the
molecules increases as the size increases.
Polar solutes dissolve in polar solvents.
Water is a polar solvent hence carboxylic acids are
soluble in water.
The small carboxylic acids are completely soluble in
water however solubility decreases as the number of
carbon atoms increases.
When carboxylic acids dissolve in water, they ionise to a
small degree to form hydrogen ions (H+), hence they are
weak acids.
The strength of the reactions decreases as
the number of carbon atoms in the molecule
increases.
Carboxylic groups react with alcohols to form an
ester and water.
The reaction is known as a esterification and a
catalyst (concentrated sulfuric acid) and heat is
required
Since water is loss, the reaction may also be referred
to as a condensation reaction.
Esters are sweet smelling oily liquids found
naturally in fruits and flowers.
During hydrolysis, a substance is broken down by
reaction with water. Esters are hydrolysed by boiling
with a dilute aqueous acid or dilute aqueous alkali.
1. Acid hydrolysis- this yeilds the acid and alcohol
that formed the ester.
2. Alkaline hydrolysis- this yeilds the salt of the acid
and alcohol that formed the ester.
Saponification is the process by which fats and oils are
hydrolysed to form soap by boiling with concentrated
sodium hydroxide solution.