1. Esters
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2. Name / Draw these molecules
a) b) c) d) e) 2-methylpentan-1-ol f) Pentanoic acid
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Esters
Recognise an ester molecule and the ester link functional group
Name esters and draw the structural formulae for esters
Describe some uses of esters
Explain the formation and break down of esters by condensation and hydrolysis
Name and draw the reactants and products of a condensation or hydrolysis reaction

4. What are Esters?
An ester is a compound which is formed when a carboxylic acid reacts with an alcohol. They contain the Ester Link functional group (-COO-) The name of the parent alcohol and carboxylic acid give the ester it’s name. It is easy to spot an ester from it’s name; Ester names always finish with “oate” Esters can be natural or synthetic and have many uses related to their properties.
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5. Esters
Esters are formed when an alcohol reacts with a carboxylic acid, water is also produced during this reaction.
Carboxylic acid Alcohol → Ester water +
→ H2O
Ester link
The functional group of an ester is the ester link
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6. made by reacting ethanol with propanoic acid
Naming Esters
The name of the ester is made up of two parts the alcohol (__yl) part and the carboxylic acid (___anoate) part.
ethyl propanoate
made by reacting ethanol with propanoic acid
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7. Naming Esters methanol + methanoic acid  methyl + water methanoate
Ester link
methanol + methanoic acid  methyl water
methanoate
Studies have revealed that the oxygen atom in the main chain of the ester always comes from the alcohol.
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8. Propanol & Ethanoic acid Butanol & Pentanioc acid
Name the esters that the following alkanols and alkanoic acids would produce.
Propanol & Ethanoic acid
Butanol & Pentanioc acid
Propanoic acid & Methanol
Methanoic acid & Pentanol
Butanol & Butanoic acid
Octanol & Octanoic acid
Ethanoic acid & Heptanol
Propyl ethanoate
Butyl pentanoate
Methyl propanoate
Pentyl methanoate
Butyl butanoate
Octyl octanoate
Heptyl ethanoate
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9. Making Esters
Esters can be prepared by reaction of an alcohol with a carboxylic acid:
The reaction is slow at room temperature and the yield of ester is low. The rate can be increased by:
1) heating the reaction mixture
using concentrated sulphuric acid as a catalyst.
The presence of the concentrated sulphuric acid also increases the yield of ester.
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10. Collect an experiment work card from the front.
Making esters (2.4)
Acid
Alcohol
Collect an experiment work card from the front.
Notes:
Copy the above diagram and explain the purpose of the concentrated sulphuric acid; the wet paper condenser and the water bath.
What two pieces of evidence would indicate that an ester had been formed?
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11. Properties of Esters
1. Esters are ______________. so we never use a naked flame near them, we would use a heating mantle or a water bath as a source of heat.
 2. Esters have a distinctive When using them we must ensure that we have
 3. Esters are very (meaning that they turn into a
very easily)
 4. Esters are in water (they form a layer with water or other solutions).
 If you learn these properties their uses are easier to recall in an exam.
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12. Uses of esters: Flavours and Scents
Many esters are used as flavourings and in perfumes.
Natural fruit flavours contain subtle blends of some of the esters in the table below:
Name
Shortened Structural Formula
Odour/Flavour
CH3(CH2)4CH3
Banana
Methyl Butanoate
Pineapple
3-Methylbutyl Butanoate
CH3(CH2)2(CH2)2CH(CH3)2
Apple
CH3COOC3H7
Pear
Methyl-1-butyl ethanoate
CH3COOCH(CH3)C4H9
2-Methylpropyl methanoate
Raspberry
C3H7COOC5H11
Apricot, Strawberry
Benzyl ethanoate
CH3COOCH2C6H5
Peach, flowers
Methyl 2-aminobenzoate
C6H4(NH2)COOCH3
Grapes
Benzyl butanoate
C3H7COOCH2C6H5
Cherry
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14. Uses of esters: Solvents
Esters are also used as non-polar industrial solvents.
Some of the smaller esters are quite volatile and are used as solvents in adhesives, inks and paints – pentyl ethanoate is used in nail varnish for example.
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15. Uses of esters: Decafination
Ethyl ethanoate is one of a number of solvents used to extract caffeine from coffee and tea.
De-caffeinated products produced with ethyl ethanoate are often described on the packaging as "naturally decaffeinated" because ethyl ethanoate is a chemical found naturally in many fruits.
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16. Decafination (2.5)
Caffeine (C8H10N4O2) is an example of a class of compounds called alkaloids which are produced by plants.
The name alkaloid means “alkali-like”, where alkali is a base and hence refers to these basic properties.
Carry out the experiment to extract caffeine from tea.
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17. Uses of esters
Caffeine is more soluble in the organic solvent ethyl ethanoate than in water, so we will extract caffeine into the organic solvent to separate it from glucose, tannins, and other water soluble compounds using a separating funnel.
The ethyl ethanoate portions can be combined and the ethyl ethanoate removed by evaporation to leave the caffeine .
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18. Hydrolysis of Esters (2.6)
Condensation
Alcohol Carboxylic Acid ⇌ Ester + Water
Hydrolysis
The ester is split up by the chemical action of water, hydrolysis.
The hydrolysis and formation of an ester is a reversible reaction. R C O H +
Bonds broken
Ester + Water + R C O H
Bonds formed
Carboxylic Acid + Alcohol
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19. Hydrolysis of an Ester
To reverse the formation of ester (ie hydrolyse it) we need to react the ester with water.
However in practice the ester is heated with either dilute acid or dilute alkali.
The ester is said to be heated under “reflux”.
When sodium hydroxide solution is used the ester is ‘split up’ into the alkanol and the sodium salt of the acid.
The alkanol can be removed by distillation and the alkanoic acid can be regenerated by reacting the sodium alkanoate with dilute hydrochloric acid.
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20. Starter Questions
Name the products formed by hydrolysis of each of the following compounds:
ethyl ethanoate
CH3CH2OOCCH2CH2CH3
propyl butanoate
CH3OOCH
butyl pentanoate
methyl hexanoate
pentyl methanoate
CH3CH2CH2OOCCH3 

21. Fats and Oils Learning Outcomes
By the end of these lessons you will be able to:
Explain the chemistry and structure of edible fats and oils.
Explain the difference in melting points of fats and oils in terms of structural differences.

22. Fats in the Diet Fats provide more energy per gram than carbohydrates.
Fat molecules are insoluble, and tend to group together and form a large droplet. This is how fat is stored in the adipose tissue.
We store our extra energy as fat. The type of fat we eat is important. Animal fats contain important fat soluble vitamins. Oils, are thought to be healthier than solid fats, as they are less likely to be deposited inside our arteries. However, there is an ongoing debate about which fats are better for us.
Polyunsaturated fats are considered to be less potentially harmful to the heart.

23. Fats and oils are: A concentrated source of energy
Essential for the transport and storage of fat-soluble vitamins in the body
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24. Fats and oils Naturally occuring Animal fat Vegetable oil Marine oil
lard
suet
sunflower oil
coconut oil
cod liver oil
whale oil

25. Fats and Oils Glycerol propan-1,2,3-triol 50% of your brain is fat!
Fats and oils are a range of substances all based on glycerol,
propan-1,2,3-triol.
Natural fats and oils are a mixture of triglyceride compounds.
Each -OH group can combine chemically with one carboxylic acid molecule.
The resulting molecules are fats and oils. They are described as triglycerides.
The hydrocarbon chain in each carboxylic acid can be from 4 to 24 C’s long.
The C’s can be single bonded (saturated) or double bonded (unsaturated).
Glycerol
propan-1,2,3-triol

26. Fats and oils
Both fats and oils are built from glycerol; an alcohol with three -OH groups.
glycerol
Systematic name is propane-1,2,3-triol

27. The other components of fat molecules are carboxylic acids.
Long chain carboxylic acids are known as Fatty Acids.
One such fatty acid is Stearic acid:
Stearic acid
Systematic name is octadecanoic acid

28. Examples of Fatty Acids
C17H35COOH
CH3(CH2)16COOH
Stearic Acid (suet, animal fat) Saturated
Oleic Acid (olive oil) Unsaturated
C17H33COOH
CH3(CH2)7CH=CH(CH2)7COOH

29. The glycerol molecule and fatty acids form ester links.
Fats and oils are ESTERS made from glycerol and long chain carboxylic acids

30. The formation of the ester links is an example of a condensation reaction. Formation / removal of water in the condensation reaction gives -
The molecular formula shown above suggests that the fat
molecule is shaped like an E, but the molecule is actually
shaped more like this:

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Practice Questions

32. Melting point of fats and oils
Explain how differences in structure of fats and oils lead to differences in strength of intermolecular forces
Describe the effect this has on the melting points of fats and oils.

33. Fats are mainly built from carboxylic acids with C-C single bonds
Fats are mainly built from carboxylic acids with C-C single bonds. (SATURATED)
Stearic acid in beef fat
Oils have at least one C=C bonds in the carboxylic acids from which they are made. (UNSATURATED)
Oleic acid in olive oil

34. Oil Fat Double bonds in oil change the shape of the molecules.
This makes the molecule less compact.
Less tightly packed molecules result in weaker bonds between the molecules this makes oils liquid.
Fat
Fat molecules pack together more tightly, making fats solid at room temperature.

35. In general oils have a higher proportion of unsaturated molecules.
In practice both fats and oils are mixtures of esters containing both saturated and unsaturated compounds.
Beef Fat
Olive oil
In general oils have a higher proportion of unsaturated molecules.

36. How do the melting points of the fats compare with the melting points of the oils?
What is meant by saturated and unsaturated?
How does the proportion of unsaturated molecules in an oil compare with that in a fat?
Explain why fats are likely to have relatively high melting points and oils are likely to have relatively low melting points.

37. Unsaturation in fats and oils (2.8)
Using a plastic pipette, add five drops of olive oil to 5 cm3 of hexane in a conical flask.
2. Use a burette filled with a dilute solution of bromine water (0.02 mol/L)
(Harmful and irritant).
3. Read the burette.
4. Run the bromine water slowly into the oil solution. Shake vigorously after each addition. The yellow colour of bromine disappears as bromine reacts with the oil. Continue adding bromine water to produce a permanent yellow colour.
5. Read the burette. Subtract to find the volume of bromine water needed in the titration.
6. Repeat the experiment with: five drops of cooking oil (vegetable) and five drops of cooking oil (animal).
Oil and hexane

38. Add 2cm3 of ethanol to a clean test tube.
Method:
Add 2cm3 of ethanol to a clean test tube.
Add 3 drops of the first oil to be tested stopper the tube and shake to dissolve.
Add 1 drop of bromine solution and shake until solution becomes colourless.
Repeat until no change occurs and note the number of drops required.
Repeat with other oils being tested.
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39. The degree of saturation in a fat or oil can be determined by the
Iodine Number. (bromine can also be used).
The iodine reacts with the C=C bonds, so the greater the iodine number, the greater the number of double bonds.
Fat
Av Iodine No
Butter 40
Beef Fat 45
Lard 50
Olive Oil 80
Peanut Oil
100
Soya Bean Oil
180
Solid fats – butter, beef fat & lard have low iodine numbers because they are more saturated than the unsaturated oils.
Margarine is made from vegetable oils, butter from animal fats. One reason why margarine spreads better!
Omega 3 fatty acids make up a large % of your brain’s fat.

40. Hydrogenation
The addition of hydrogen to an unsaturated oil will ‘harden’ the oil.
This will Increase its melting point.
The hydrogen is added across the double bond.
Used with margarine, otherwise margarine would be a liquid when taken out of the fridge.

41. Melting point of fats and oils
I can explain how differences in structure of fats and oils lead to differences in strength of intermolecular forces
I can describe the effect this has on the melting points of fats and oils.
Soaps

42. Hydrolysis of Esters
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43. Soaps explain how soaps are produced
relate the cleansing action of soaps to the structure of the soap molecules.

44. Structures of fats and oils - Revision
Fats and Oils are esters of glycerol and long chain fatty acids.
Hydrolysis of a fat or oil produces glycerol (alcohol) and 3 carboxylic acids / fatty acids.
Hydrolysis
Fatty Acids + Glycerol
Fatty acid part
(R 1, 2, 3 are long carbon chains,
which can be the same or different)
Glycerol
part

45. Hydrolysis To hydrolyse an ester we need to react it with water.
However in practice the ester is heated under “reflux” with either dilute acid or dilute alkali.
When sodium hydroxide solution is used the ester is ‘split up’ into the alkanol and the sodium salt of the acid.
The alkanol can be removed by distillation and the alkanoic acid can be regenerated by reacting the sodium alkanoate with dilute hydrochloric acid.
The equations for these reactions are:
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46. Soaps Soaps are salts of fatty acids.
Soaps are formed by the alkaline hydrolysis of fats and oils by sodium or potassium hydroxide by boiling under reflux conditions:
+ 3
Na+
+ 3NaOH
Sodium stearate
(soap)
Glycerol
Glyceryl tristearate

47. Structure of Soaps
As most of the grime and dirt on skin, clothes and dishes tends to be trapped in oils and greases, water alone cannot rinse away the muck.
If the oils/greases can be made to mix with water then it becomes easy to wash off, along with the grime.
Soaps and detergents do this job in a clever way, due to the structure of the molecules:
Sodium or potassium salts of long chain fatty acids really have two quite separate parts in terms of their bonding types – a long hydrocarbon chain which is non polar and an ionic ‘head’.
COO-
Na +
Hydrophobic
tail
Hydrophilic
head
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48. Structure of soap
COO-
Na +
Hydrophobic
tail
Hydrophilic
head
The long covalent hydrocarbon chain “tail” gives rise to the hydrophobic (water hating) and oil-soluble (non-polar) properties of the soap molecule (represented in yellow).
The charged carboxylate group “head” (represented in blue) is attracted to water molecules (hydrophilic). In this way, soaps are composed of a hydrophilic head and a hydrophobic tail:

49. Cleansing action of soaps
The following ball and stick diagram represents the initial interaction of soap on addition to water and material with a grease stain:
(blue for hydrophilic head group)
(yellow for hydrophobic tail group)

50. When the solution containing soap and water is agitated (stirred vigorously) the interactions of hydrophobicity and hydrophilicity become apparent. The hydrophobic, non-polar, tails burrow into the greasy, non-polar molecule – like attracting like. In the same way the polar hydrophilic head groups are attracted to polar water molecules. The head groups all point up into the water at the top of the grease stain.

51. The attraction of the head group to the surrounding water, via polar-to-polar interactions, is so strong that it causes mechanical lift of the grease molecule away from the material on which it was deposited. The hydrophobic tails are anchored into the grease due to non-polar to non-polar attraction. In combination, these effects allow for the removal of the grease stain.

53. MICELLE
grease
particle
Na+ -

54. The hydrophobic tails dissolve in the oil or grease.
Soaps can be used to remove non-polar substances such as oil and grease.
Soap ions have long non-polar tails, readily soluble in non-polar compounds (hydrophobic), and ionic heads that are water-soluble (hydrophilic).
The hydrophobic tails dissolve in the oil or grease.
The negatively-charged hydrophilic heads remain in the surrounding water.
Agitation causes ball-like structures to form.
The negatively-charged ball-like structures repel each other and the oil or grease is kept suspended in the water.
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55. These remove oil and grease in the same way as soap.
Hard water is a term used to describe water containing high levels of dissolved metal ions.
When soap is used in hard water, scum, an insoluble precipitate, is formed.
Soapless detergents are substances with non-polar hydrophobic tails and ionic hydrophilic heads.
These remove oil and grease in the same way as soap.
Soapless detergents do not form scum with hard water.
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56. Soaps
I can explain how soaps are produced by alkaline hydrolysis of fats and oils
I can relate the cleansing action of soaps to the hydrophobic and hydrophilic nature of soap molecules.
Emulsions

58. Emulsions
Describe the characteristics of an emulsion, and study the chemistry of typical emulsifier molecules.

59. Emulsifiers
An emulsion contains small droplets of one liquid dispersed in an another liquid.
Emulsions in food are mixtures of oil and water.
To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added.

60. Emulsifiers
Expt 2.8 (b)

61. Emulsifier molecules
Emulsifiers for use in food are commonly made by reacting edible oils with glycerol to form molecules in which either one or two fatty acid groups are linked to a glycerol backbone rather than the three normally found in edible oils.
The one or two hydroxyl groups present in these molecules are hydrophilic whilst the fatty acid chains are hydrophobic.
The presence of this emulsifier is shown on packaging by E-numbers, E471 and is one of the most common on food packaging.

62. Emulsifiers Mayonnaise contains oil and water.
The emulsifier keeps these mixed and without it the oil and water separate.

63. Foods that Commonly Contain Emulsifiers
Emulsifiers in food
Emulsifiers are among the most frequently used types of food additives. They are used for many reasons:
Foods that Commonly Contain Emulsifiers
Biscuits
Toffees
Bread
Extruded snacks
Chewing gum
Margarine / low fat spreads
Breakfast cereals
Frozen desserts
Coffee whiteners
Cakes
Ice-cream
Topping powders
Desserts / mousses
Dried potato
Peanut butter
Soft drinks
Chocolate coatings
Caramels
Emulsifiers can help to make a food appealing.
They are used to aid in the processing of foods and also to help maintain quality and freshness.
In low fat spreads, emulsifiers can help to prevent the growth of moulds which would happen if the oil and fat separated.

64. Emulsifiers in food Foods that Commonly Contain Emulsifiers Biscuits
Toffees
Bread
Extruded snacks
Chewing gum
Margarine / low fat spreads
Breakfast cereals
Frozen desserts
Coffee whiteners
Cakes
Ice-cream
Topping powders
Desserts / mousses
Dried potato
Peanut butter
Soft drinks
Chocolate coatings
Caramels

65. Proteins Soaps and Emulsions
I can explain how soaps are produced by alkaline hydrolysis of fats and oils
I can relate the cleansing action of soaps to the hydrophobic and hydrophilic nature of soap molecules.
I can define an emulsion.
I can explain why emulsifiers are added to food.
I can describe how emulsifiers are made and how they work
Proteins