2.4 esters, fats and oils Flashcards
What is the functional group of an ester?
ester link
-COO-
What are 3 uses of esters?
- flavourings
- fragrances
- solvents for non-polar compounds that do not dissolve in water
What reaction forms an ester and what are the reactants?
condensation reaction between an alcohol and a carboxylic acid
What is a condensation reaction?
two molecules are joined together with the elimination of a small molecule
When an ester is formed by the reaction between a hydroxyl group and a carboxyl group, what small molecule is eliminated?
water
What can esters be hydrolysed to produce?
an alcohol and a carboxylic acid
What is a hydrolysis reaction?
a molecule reacts with water to break down into smaller molecules.
What family are edible fats and edible oils a part of?
esters
What is the systematic name for glycerol?
propane-1,2,3-triol
How are edible fats and edible oils formed?
formed in the condensation reaction of glycerol and three fatty acid molecules
What are long carbon chain, straight chain carboxylic acids called?
fatty acids
-they can be saturated or unsaturated
What is the difference is melting points of edible oils and edible fats?
edible oils have lower melting points than edible fats
Why do edible oils have lower melting points than edible fats?
- double bonds in fatty acid chains prevent oil molecules from packing closely together
- the greater the number of double bonds present, the weaker the London dispersion forces
- the greater the degree of unsaturation, the lower the melting point
How do you test for unsaturated compounds and how does it work?
- unsaturated compounds quickly decolourise bromine solution
- the bromine molecules add across the carbon-carbon double bonds in an addition reaction
- oils with a higher degree of unsaturation will require a higher volume of bromine solution than oils with a lower degree of unsaturation
Name 2 reasons why fats and oils are important
- they are a concentrated source of energy
- essential for the transport and storage of fat-soluble vitamins in the body (due to their non-polar structure)
What is produced in the hydrolysis of edible fats and oils?
- 3 fatty acid molecules
- 1 glycerol molecule
Will fats or oils decolourise bromine solution?
oils as they are unsaturated molecules
How are esters named?
-the first part of the name which ends in -yl comes from the alcohol
-the second part of the name which ends in -oate comes from the acid
ethanol+methanoic acid
–>ethyl methanoate
Why do esters have a lower boiling point than carboxylic acids and alcohols and why can they not dissolve in water?
they do not contain a hydroxyl group. therefore esters cannot form hydrogen bonds to neighbouring ester molecules
- less energy needed to separate molecules
- non polar
What type of ester are edible fats and edible oils?
triester
-containing three ester links
Why is glycerol so viscous and have a high boiling point compared to other alcohols?
- it has three -OH groups
- allows the glycerol molecules to form more hydrogen bonds between molecules than alcohols with only a single -OH group
explain the difference between how fats are formed and how oils are formed?
- fats are formed from saturated fatty acids
- oils are formed from unsaturated fatty acids
What is another name for fats and oils?
triglyceride
Explain the packing of edible fats
- the efficient packing
- allows for the London dispersion forces to hold the fat molecules together
- these are greater between fat molecules than between oil molecules because of this efficient packing.
- this means that it will take more energy to separate fat molecules and so the melting point will be higher than oils
- solid at room temperature
Explain the packing of edible oils
- the double bonds cause the molecules to have a distorted structure, which makes it difficult for them to pack closely together
- this results in fewer London dispersion forces between oil molecules
- it therefore takes less energy to break apart the oil molecules
- meaning that oils have a lower melting point than fats
What is the catalyst used when producing an ester?
concentrated sufuric acid
What is formed during the hydrolysis of an ester?
alcohol + carboxylic acid
What are 2 observations that would show you have an ester?
- layers
- smell
Where does an ester link break during hydrolysis?
between the carbon of the carboxylic acid and the oxygen
- H is added to the alcohol
- OH is added to the carboxylic acid
Fats and oils belong to which family of compounds?
esters
What is the catalyst used during esterification?
concentrated sulphuric acid
why would you use a condenser during esterification?
to condense any vapours or reactants/products which evaporate
