2A Esters, Fats & Oils Flashcards
Why are oils liquid?
Explain fully.
Oils are made using mostly unsaturated fatty acids that cannot pack closely together, as C=C bonds present distort chains.
= decreased ldf forces (intermolecular forces).
= less energy being required to separate the oil molecules.
= mpt/bpt’s are lower than fats.
Alcohol reacting with carboxylic acid to produce an ester is an example of what type of chemical reaction.
Condensation (and esterification).
What sort of acids are used to produce fats/oils?
Long, chain fatty acids.
Fatty carboxylic acids.
Natural fats and oils can be classified according to their origin.
Give 3 examples of where fats/oils can be found naturally.
Plant
Animal
Marine
How many hydroxyl groups are present in glycerol?
3
Glycerol is a trihydritic alcohol.
Glycerol is a triol.
True of false?
“Fatty acids can be saturated.”
True.
e.g. C17H35COOH = Saturated fatty acid.
The number of H is twice the number of C (2 x 17 = 35), so only C-C single bonds present.
State 2 uses of esters.
- Solvent.
- Flavouring.
Give two pieces of evidence that show an ester has been formed in esterification.
- Oily layer on top of the water.
- Characteristic ester smell.
Esters are produced when which two substances react together?
- Alcohol
- Carboxylic acid
What is the chemical name for a fat or oil (i.e. an ester of glycerol and three fatty acid molecules)?
Triglyceride
How many moles of fatty acid reacts with 1 mole of glycerol, when a fat/oil is produced in a condensation reaction?
3 moles of fatty acid react with 1 mole of glycerol.
What is a hydrolysis reaction?
The chemical breakdown of a molecule by reaction with water.
True of false?
“Fatty acids can be saturated.”
True.
e.g. C17H33COOH = Unsaturated fatty acid.
The number of H is NOT twice the number of C (2 x 17 = 35 and there are only 33), so ONE C=C double bond present.
For every 2 H atoms “missing” this identifies ONE C=C bond.
Why is a wet paper towel wrapped around the top of the test tube used for an esterification reaction?
To act as a condenser, to stop the escape of products from test tube.
Why is a cotton wool plug used in the opening of the test tube used for an esterification reaction?
To stop hot acid escaping from the test tube.
What family of chemical compounds do fats/oils belong to?
Esters
Name a “reversible” chemical reaction.
Esterification.
Methanoic acid and hexanol produce which ester?
Hexyl methanoate.
Butanol and ethanoic acid would produce which ester?
Butyl ethanoate
State two properties of esters.
- Insoluble in water.
- Characteristic smell.
How many moles of water are produced when a fatty acid is produced in a condensation reaction?
3 moles of water produced. One for each ester link formed.
What is a condensation reaction?
When two molecules react together to produce one larger molecule with loss of water.
Why are fats/oils essential for humans?
For the transport and storage of fat soluble vitamins in the body.
Why are fats solid?
Explain fully.
Fats are made using mostly saturated fatty acids. These acids can pack closely together.
= increased ldf forces (intermolecular forces).
= more energy being required to separate the fat molecules.
= mpt/bpt’s are higher than oils.
Methyl pentanoate was formed from which alcohol and carboxylic acid?
Methanol
Pentanoic acid
Name the alcohol used to make fats/oils.
Glycerol
Propan-1,2,3-triol
Why is the esterification reaction mixture poured into a beaker containing an aqueous solution of sodium hydrogencarbonate?
To neutralise the sulfuric acid and obtain the ester.
Why is concentrated sulfuric acid used in an esterification reaction?
Conc. sulfuric acid acts as a catalyst in an esterification reaction.
It also acts as a dehydrating agent (it removes water) to help prevent the reverse reaction from taking place.
