Chapter 33 – The aldehydes and the ketones
Section A – Structures of the aldehydes and the ketones
The aldehydes
The aldehydes are a homologous series with the functional group: __________, this means that they
all contain a carbonyl group (________), where at least one of the atoms attached to the carbon of
the carbonyl group is a ________________.
Methanal
Ethanal
Propanal
Butanal
Benzaldehyde
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Chapter 33 – The aldehydes and the ketones
The ketones
The ketones are a homologous series with the functional group: __________, this means
that they all contain a carbonyl group (________), and each group attached to the carbon of
the carbonyl group is an alkyl group.
Propanone
Butanone
Use:
Section B – Physical Properties
Melting and boiling points
Aldehydes and Ketones have _____________ melting and boiling points than their corresponding
alkanes. This is due to the presence of the carbonyl group (___________) which is highly polar, and
allows the formation of _______________ ____________ intermolecular forces between the
molecules.
However they cannot form intermolecular hydrogen bonds as the alcohols can, so they have
___________ melting and boiling points than their corresponding alcohols.
Solubility in water
The lower members of the aldehydes and ketones are _____________ in water. The presence of the
polar _______ bond allows them to dissolve with water efficiently (Hydrogen bonding can occur)
The higher members of the aldehydes and ketones are ____________ soluble in water. This is
because in these the non polar alkyl chain gets longer and its effect becomes more significant.
Section C – Formation of aldehydes and Ketones from alcohols
In the previous chapter we studied the formation of aldehydes by the ____________ of __________
alcohols, using acidified ___________ dichromate. The formation of ketones is achieved by the
____________ of __________ alcohols, using acidified ___________ dichromate.
Aldehydes can be produced by the ________________ of their corresponding carboxylic acids using
hydrogen gas and a hot nickel catalyst.
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Chapter 33 – The aldehydes and the ketones
Section D – Chemical reactions of the aldehydes and ketones
Oxidation reactions
Aldehydes can be oxidised to form their corresponding carboxylic acids by reaction with acidified
sodium dichromate solution
Example
Ethanal
Ethanoic acid
***Ketones cannot take part in this kind of reaction!
Reduction reactions
 Aldehydes can be reduced to their corresponding primary alcohols by reaction with hydrogen gas
passed over a hot Nickel catalyst.
Ethanal
Ethanol
 Ketones can be reduced to their corresponding secondary alcohols by reaction with hydrogen gas
passed over a hot Nickel catalyst.
Propanone
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Propan – 2- ol
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Chapter 33 – The aldehydes and the ketones
Section E – Mandatory experiment: To study the following reactions…
Part 1 :Reaction of Ethanal with acidified potassium permanganate solution
1. Some _______________________potassium permanganate solution is placed in a test-tube.
2. Some Ethanal is added
3. The test tube is warmed in a hot beaker of water
Result: The potassium permanganate changes colour from _____________ to _________________,
Explanation: The Ethanal reacts with the acidified potassium permanganate and is oxidised to
_______________ acid. As this occurs the Mn(7) ions which are _____________ in colour and are
reduced to Mn (2) ions which are __________________.
Half reaction equations:
Part 2: Reaction of Ethanal with Fehling’s solution
1. Some Fehling’s solution is placed in a test-tube.
2. Some Ethanal is added
3. The test tube is warmed in a hot beaker of water
Result: The Fehling’s solution changes colour from _____________ to _________________,
Explanation: The Ethanal reacts with the Fehling’s solution and is oxidised to _______________
acid. As this occurs the Cu+2 ions from the Fehling’s solution which are _____________ in colour are
reduced to Cu +1 ions which are __________________ in colour.
Half reaction equations:
Part 3: Reaction of Ethanal with ammonical silver nitrate solution – The ___________mirror test.
1. Some Tollens reagent is placed in a test-tube( This is made from mixing silver nitrate, dilute
_____________ hydroxide and dilute ___________ solution together)
2. Some Ethanal is added
3. The test tube is warmed in a hot beaker of water
Result:
A
silver
___________
is
formed
inside
the
test-tube.
Explanation: The Ethanal reacts with Tollens reagent and is oxidised to _______________ acid. As
this occurs the Ag+ ions from the Tollens reagent which are _____________ are reduced to Ag
which are a shiny silver colour.
Half reaction equations:
Note that none of these reactions would occur with ketones and so these
tests can be used to distinguish between an aldehyde and a ketone
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Chapter 33 – The aldehydes and the ketones
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Organic Chemistry - The Aldehydes and the ketones
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Do you know about…
Structure of aldehydes
Aldehydes: structure and names up to C-4. Geometry of carbon
atoms.
Presence of carbonyl group
Physical properties of the alcohols
[physical state and explanation of boiling points of the members
of the family compared to corresponding alkanes, and each
other}
Solubility (qualitative only) in water and explanation and in nonpolar solvents
Uses of aldehydes
Benzaldehyde in almond kernels
Reactions of aldehydes
Oxidation of alcohols using Na2Cr2O7 to (i) aldehydes and (ii)
acids(equations required).
Reduction of carbonyl compounds using H2/Ni catalyst.
(equations required).
Mandatory experiment – reactions of aldehydes with acidified
potassium permanganate, Fehlings solution and Tollens reagent
Structure of ketones
Ketones: structure and names up to C-4. Geometry of carbon
atoms.
Presence of carbonyl group
Physical properties of the ketones
[physical state and explanation of boiling points of the members
of the family compared to corresponding alkanes, and each
other}
Solubility (qualitative only) in water and explanation and in nonpolar solvents
Uses of ketones
Propanone in nail varnish remover
Reactions of ketones
Oxidation of secondary alcohols using Na2Cr2O7 to ketones.
REACTION CAN GO NO FURTHER!!
Reduction of carbonyl compounds using H2/Ni catalyst.
(equations required).
The three tests to distinguish ketones from alcohols –
reagents used and results obtained
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