Chemistry Notes II

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  • Created on: 19-03-12 10:31
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Oxidation of alcohols
Alcohols are oxidised with acidified dichromate ions (Cr2O72)
This mixture can be made from potassium dichromate and sulphuric acid. (K2CrO7)
During the reaction, the acidified potassium dichromate changes colour from orange to green.
Primary alcohols
Primary alcohols are oxidised to aldehydes and then carboxylic acids and water
For carboxylic acid, reflux
For aldehyde, distil
Secondary alcohols
Oxidised to ketones only.
Reactions of aldehydes and ketones
Aldehydes and ketones can be reduced to alcohols by using warm NaBH4
Nucleophillic addition
React with NaBH3
BH4 acts as source of hydride ions
See Figure 6 in book
Carboxylic acids
Functional group ­COOH
Carboxylic acids with less than 4 carbons are very soluble in water. The highly polar C=O and OH
bonds allow carboxylic acid molecules to form hydrogen bonds with water molecules. As the
number of carbons increases, the solubility decreases.
Carboxylic acids are relatively weak.

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Carbonyl Compound Tests
Aldehydes and ketones can be detected using 2, 4dinitrophenylhydraxine (2, 4DNP)
A solution of 2, 4DNP with methanol and sulphuric acid is known as Brady's reagent.
If an aldehyde or ketone is present then the solution will turn yellow or orange.
Only works for aldehyde and ketones.
Tollen's reagent is a weak oxidising agent used to distinguish between aldehydes and ketones.
Aldehydes are easily oxidised to carboxylic acids by Tollen's reagent. Ketones are not.…read more

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Triglycerides and health
Fats and oils come from saturated or unsaturated fatty acids
Foods high in saturated fats are bad for you ­ increased risk of heart disease by raising
blood cholesterol levels.
Unsaturated fats were presumed to be healthy but they can exist in two states: cis and Trans
Cis groups on same side
Trans Groups on opposite sides.
In nature, fatty acids exist in the cis form.…read more

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Ethyl/methyl ester of a fatty acid. Made by transesterification.
React triglycerides with methanol/ethanol with sodium/potassium hydroxide.
Fats and oils are esters of long chain carboxylic acids called fatty acids. Fats are solid and
oils are liquid.
Triglycerides are triesters of glycerol (propane1, 2, 3triol) and 3 fatty acids joined to each
of the alcohol groups through an ester linkage.
Fatty acids can be saturated or unsaturated. Most natural fatty acids have an even number
of carbons.…read more

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Esterification is the reaction of an alcohol with a carboxylic acid to produce an ester and water.
Esters can be made by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst
(Sulphuric acid)
See diagram in book
Esters can also be prepared by heating an acid anhydride with an alcohol.
See diagram in book
An acid anhydride is formed by the removal of water from two carboxylic acid molecules.…read more

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Addition polymerisation
All the atoms in the monomer are used. Made from a monomer with C=C bond.
Condensation Polymerisation
Monomers join up with the expulsion of small molecules. Not all the original atoms are present in the
polymer. Can be made from monomers with 2 different functional groups.…read more

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In a polyamide, the monomers have a carboxyl group, COOH and an amine group, NH2
Polyamides can be made from two different monomers a carboxylic acid monomer and an amine
monomer, or they can be made from one type of monomer with both functional groups
(polypeptides and proteins).
During polymerisation:
A bond forms between an amine group and a carboxyl group
An amide link forms and water is eliminated.…read more

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