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Duncanrig Secondary School cfe Higher Chemistry Natures Chemistry

Duncanrig Secondary SchoolCfE Higher Chemistry

Unit 2Natures Chemistry

Part 1 Esters, Fats and OilsPart 2 Proteins Part 3 Oxidation of Foods and Chemistry of CookingPart 4 Soaps, Detergents and EmulsionsPart 5 Skincare and Fragrances

Esters, Fats and Oils

No. Learning Outcome Understanding?

1 Esters are formed by the condensation reaction between a carboxylic acid and an alcohol.

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2 In a condensation reaction the molecules join together with the elimination of water.

3 The ester link is formed by the reaction of a hydroxyl group with a carboxyl group.

4 An ester can be identified from the name containing the “-yl and -oate” endings.

5An ester can be named given the names of the parent carboxylic acid and alcohol.

6Structural formulae for esters can be drawn given the names of the parent carboxylic acid and alcohol or the names of esters.

7 Esters can be hydrolysed to produce a carboxylic acid and alcohol.

8 In a hydrolysis reaction a molecule reacts with water, breaking down into smaller molecules.

9Given the name of an ester or its structural formula, the hydrolysis products can be named and structural formula can be drawn.

10 Esters have characteristic smells and are used as flavourings, fragrances and solvents.

11Fats and oils in the diet supply the body with a more concentrated source of energy than carbohydrates.

12 Fats and oils are essential for the transport and storage of fat soluble vitamins in the body.

13Fats and oils are esters formed from the condensation of glycerol and 3 carboxylic acids known as fatty acids.

14Fatty acids can be saturated or unsaturated straight chain carboxylic acids containing even numbers of carbon atoms ranging from C4 to C24.

15The lower melting point of oils compared to those of fats is related to the higher degree of unsaturation in oil molecules.

16

The unsaturated bonds in oils means that the molecules can’t pack as close together resulting in weaker van der Waals forces between the molecules and therefore less energy is needed to separate them.

Proteins


1Proteins are the major structural materials of animal tissue.

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2Proteins are involved in the maintenance and regulation of life processes.

3Enzymes are biological catalysts made from protein.

4

Amino acids, the building blocks from which all proteins are formed, are relatively small molecules which all contain an amino group (NH2) and a carboxyl group (COOH).

5

The body cannot make all the amino acids required for body proteins and is dependent on dietary proteins for supply of certain amino acids known as essential amino acids.

6Proteins are made of many amino acid molecules linked together by condensation reactions.

7

In these condensation reactions, the amino group on one amino acid and the carboxyl group of a neighbouring amino acid join together, with the elimination of water.

8The link which forms between two amino acids can be recognised as an amide link (CONH) also known as the peptide link.

9Proteins which fulfil different roles in the body are formed by linking differing sequences of amino acids together.

10During digestion, enzyme hydrolysis of dietary proteins can produces amino acids.

11

The structural formulae of amino acids obtained from the hydrolysis of proteins can be identified from the structure of a section of the protein.

Oxidation of Food and Chemistry of Cooking


1Branched-chain alcohols with no more than 8 carbon atoms in the longest chain can be named from structural formulae.

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2Given the names of branched-chain alcohols, structural formulae can be drawn and molecular formulae written.

3Alcohols can be classified as primary, secondary or tertiary.

4Primary alcohols are oxidised, first to aldehydes and then to carboxylic acids.

5 Secondary alcohols are oxidised to ketones.

6When applied to carbon compounds, oxidation results in an increase in the oxygen to hydrogen ratio.

7Hot copper (II) oxide or acidified dichromate solutions can be used to oxidise primary and secondary alcohols.

8 Tertiary alcohols cannot be oxidised.

9Branched-chain carboxylic acids, with no more than 8 carbon atoms in the longest chain, can be named from structural formulae.

10Given the names of branched-chain carboxylic acids, structural formulae can be drawn and molecular formulae can be written.

11Oxygen reacts with edible oils giving the food a rancid flavour.

12Antioxidants are molecules which will prevent these oxidation reactions taking place.

13Ion-electron equations can be written for the oxidation of many antioxidants.

Soaps, Detergents and Emulsions


1Soaps are produced by the alkaline hydrolysis of fats and oils to form an ionic salt.

2Soap ions have a long covalent tail, readily soluble in covalent compounds. This tail is hydrophobic.

3 Soap ions have an ionic carboxylate head which is negatively charged and water soluble. This head is hydrophilic.

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4When cleaning using soaps and detergents, the hydrophobic tails dissolve in a droplet of grease or oil whilst the hydrophilic heads face out into the surrounding water.

5Agitation of the mixture results in a ball-like structure forming with the hydrophobic tails on the inside and the negative hydrophilic heads on the outside.

6Repulsion between the negatively charged hydrophilic heads results in an emulsion being formed and the dirt released.

7 Soapless detergents are particularly useful in hard water areas.

8The ionic (hydrophilic) head in a soapless detergent does not form a solid precipitate with calcium ions or magnesium ions (which are found in hard water).

9An emulsion contains small droplets of one liquid dispersed in another liquid. Emulsions in food are mixtures of oil and water.

10To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added.

11

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. This is different to the three fatty acids usually found in edible oils.

12The one or two hydroxyl groups present in these emulsifier molecules are hydrophilic whilst the fatty acid chains are hydrophobic.

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Fragrances and skincare


1Essential oils are concentrated extracts of the volatile, non-water soluble aroma compounds from plants.

2Essential oils are widely used in perfumes, cosmetic products, cleaning products and as flavourings in food.

3 Essential oils are mixtures of organic compounds rather than just one pure compound.

4 Terpenes are key components in most essential oils.

5Terpenes are unsaturated compounds formed by joining together isoprene (2-methybuta-1, 3-diene) units.

6Terpenes are components in a wide variety of fruit and floral flavours and aromas.

7Terpenes can be oxidised within plants to produce some of the compounds responsible for the distinctive aroma of spices.

8Ultraviolet radiation (UV) is a high-energy form of light present in sunlight.

9

Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken. This process is responsible for sunburn and contributes to aging of the skin.

10 Sun-block products prevent UV light reaching the skin. 11 When UV light breaks bonds, free radicals are formed.

12Free radicals have unpaired electrons and, as a result, are highly reactive.

13Free radical chain reactions include the following steps:

Initiation Propagation Termination

14

Many cosmetic products contain free radical scavengers; molecules which can react with free radicals to form stable molecules and prevent chain reactions.

15 Free radical scavengers are also added to food products and to plastics.

Part 1 Esters,Fats and OilsNat 5 ALCOHOLS Revision

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Nomenclature and structural formulae

In an alcohol a ‘H’ from the corresponding alkane has been replaced with a covalently bonded hydroxyl functional group, an ‘OH’ .

e.g. ethane is C2H6 ethanol is C2H5OH

H H H H

HCCH HCCOH H H H H

The first members of the homologous series of alcohols are :-

General formula CnH2n+1 OHSystematic naming of alcohols

Naming alcohols has been covered in National 5. A few examples of are given below

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Alcohols can have more than 1 OH group.

Bonding and properties of alcohols

The hydroxyl functional group of the alcohols effects the properties of alcohols. In Unit 1, we found out that alcohols have higher boiling points than alkanes with a similar mass because they have hydrogen bonding between the molecules. Hydrogen bonding also effects the viscosity of the alcohol. The more hydroxyl groups present (the more hydrogen bonds present) the higher the boiling point and the more viscous the alcohol will be.

Alcohols are miscible in water because they can form hydrogen bonds with water molecules.

The alcohol is more miscible

The smaller the molecule and/or The more hydroxyl groups present

Nat 5 CARBOXYLIC ACID Revision

Nomenclature and structural formulae

Carboxylic acids contain the functional group

O of 47

Ethan-1,2-diol Propan-1,2,3-triolGlycerol


COH

This is called a carboxyl group.

The alkanoic acids are a homologous series of carboxylic acids. The first few members of the series are:

General formula CnH2n+1 COOHNote

When naming carboxylic acids we do not have to give the position of the carboxyl carbon as it is always carbon number 1.

Carboxylic acids are soluble in water as they can form hydrogen bonds with water.

ESTERS

Esters are formed in the reaction between alcohols and carboxylic acids. This is an example of a condensation reaction as two molecules join together with the elimination of a small molecule - in this case water.

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Note : When working out the structure of the ester it is essential to draw the functional group of the alcohol and the functional group of the carboxylic acid next to each other. This requires that one of the molecules is drawn in reverse of what is ‘normal’. Water can then be removed (as shown in the above example) and the correct structure of the ester molecule determined.

The first part of the esters name comes from the alcohol; the second part of the name comes from the carboxylic acid.

No. of C atoms in alcohol

First part of the name

No. of C atoms in carboxylic acid

Second part of the name

1 methyl 1 methanoate2 ethyl 2 ethanoate3 propyl 3 propanoate4 butyl 4 butanoate5 pentyl 5 pentanoate6 hexyl 6 hexanoate

e.g. the ester formed by reacting methanol (1 C atom - methyl) and propanoic acid (3 C atoms - propanoate) is called methyl propanoate.

the ester formed by reacting propanol (3 C atoms - propyl) and butanoic acid (4 C atoms - butanoate) is called propyl butanoate.

Making esters

The making of an ester is called an esterification reaction.

Alcohol + Carboxylic acid Ester + Water

Notice that the arrow in the equation is reversible which means that the reaction can occur in both directions.

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Esters are made by warming

the carboxylic acid and alcohol in a test tube containing a few drops of concentrated sulphuric acid and heated by a water bath for about 10 minutes.

Note - alcohols and the ester formed are highly flammable and should not be heated using a naked flame.

To prevent the reactants and products being lost during heating, a wet paper towel is wrapped around the outer, upper part of the test tube to act as a condenser.

Sulphuric acid is a catalyst for the reaction and acts as a dehydrating agent; it removes the water that is formed.

By removing the water from the reaction, the reverse reaction is prevented, so that more ester is made.

The ester is obtained by pouring the mixture into a beaker containing an aqueous solution of sodium hydrogencarbonate to neutralise the sulphuric acid.

Evidence that an ester is formed is its typical smell, and that it appears as a separate solid/oily liquid on top of the water.

Making Esters Write up SheetState the aim of the experiment naming the ester you made.

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Breaking esters

The breaking of an ester is called a hydrolysis reaction.

Ester + ‘Water’ Alcohol + Carboxylic acid

Esters can be broken down to form the parent alcohol and carboxylic acid, by heating with an acid or an alkali. In the laboratory, an alkali, e.g. sodium hydroxide

solution, is normally used.

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After about 30 minutes of heating under reflux, the oily layer of ester will disappear, as the ester is hydrolysed to form the parent alcohol and carboxylic acid. The alcohol and carboxylic acid could then be separated by distillation.


Note : The alcohol always comes from

‘O’ side of the ester link and the carboxylic acid from the ‘C=O’ side of the ester link. The alcohol includes the ‘O’; the carboxylic acid includes the ‘C=O’.Uses of esters

Food flavourings

Many esters are found in fruits and are also used in flavouring foods.

The following table gives the names and smells of some esters

Ester name Shortened Molecular Formula Alcohol used Carboxylic

acid used Smell

Methyl butanoate C3H7COOCH3 Methanol Butanoic acid AppleOctyl ethanoate CH3COOC8H17 Octanol Ethanoic acid OrangePropyl ethanoate CH3COOC3H7 Propanol Ethanoic acid Pear

Propyl pentanoate C4H9COOC3H7 Propanol Pentanoic acid Pineapple

Fragrances

Esters can be used as fragrances because of their sweet distinctive smell.

Solvents

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

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After about 30 minutes of heating under reflux, the oily layer of ester will disappear, as the ester is hydrolysed to form the parent alcohol and carboxylic acid. The alcohol and carboxylic acid could then be separated by distillation.


described on the packaging as "naturally decaffeinated" because ethyl ethanoate is a chemical found naturally in many fruits.

Esters are non-polar solvents and are able to dissolve many materials that water, a polar solvent, cannot dissolve. Esters are used as solvents for dyes, glues, inks as in permanent markers and whiteboard markers, nail varnish removers, car spray paints and varnishes.

Fats and Oils

Natural fats and oils can be classified according to their origin as animal, vegetable or marine.

Animal Vegetable MarineBeef fat Sunflower oil Cod liver oilPork fat Olive oil Tuna fish oil

Sheep fat Linseed oil Whale oilButterfat Palm oil Halibut liver oil

Fats are mainly solids while oils are liquids at room temperature.

Fats and Oils in the Diet

Fats and oils in the diet supply the body with energy and are a more concentrated source of energy than carbohydrates e.g. bread flour (mostly carbohydrate) contains 1420 kJ per 100g while vegetable oil contains 3700 kJ per 100g.

Too much fats or oil in our diet can lead to obesity. However, there is evidence that unsaturated oils are less harmful than saturated fats.

Fats and oils are essential for the transport and storage of fat soluble vitamins in the body. Wheras, water-soluble vitamins need regular replacement in the body, fat-soluble vitamins are stored in the liver and fatty tissues, and are eliminated more slowly than water-soluble vitamins.

Other uses of oils

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Some edible oils can be used to make alternative fuels such as bio-diesel. This is important as fuels from crude oil run out and become more expensive.

Structure of Fats and Oils

Fats and oils are esters made from glycerol and 3 carboxylic acids known as fatty acids. Glycerol (propane-1,2,3-triol) is a trihydric alcohol as it contains 3 -OH groups.

Fatty acids are long chain carboxylic acids containing an even number of carbons ranging from C4 to C24. The most common fatty acids contain C16 or C18.

The reaction between the three fatty acids and glycerol is shown below.

Fats and oils consist largely of mixtures of triglycerides in which the three fatty acid molecules which are combined with each molecule of glycerol may or may not be identical.

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Structure of Fatty Acids

Fatty acids can be saturated or unsaturated.

Fatty acid Molecular formula

Saturated/Unsaturated

Stearic acid C17H35COOH SaturatedOleic acid C17H33COOH Unsaturated

Linoleic acid C17H29COOH Unsaturated

Saturated fatty acid- stearic acid

Unsaturated fatty acids- Linoleic acid

Fats - higher degree of saturation (C-C), examples are butter and lard.

Oils - have a higher degree of unsaturation (C=C), examples are olive oil and sunflower oil.

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Melting Points of Fats and Oils

The lower melting points of oils compared to those of fats is related to the higher degree of unsaturation of oil molecules.

The presence of double bonds in oil molecules causes the long chains of atoms to become distorted. This stops the oil molecules packing as closely together as the fat molecules.

The poorer packing makes intermolecular forces, London Dispersion forces, weaker between oil molecules than between fat molecules. Less heat energy is needed to separate oil molecules and therefore oils have lower melting points than fats.

Hydrogenation

Oils can be converted into fats by a process called hydrogenation. Hydrogen is added on across the double bond in the unsaturated oil to form the more saturated fat. Partial hydrogenation produces margarine where only some of the double bonds are removed.A nickel catalyst is required for hydrogenation.

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Part 2 ProteinsFunction of proteins

Proteins are large, complex molecules found in our bodies. Each protein within the body has a specific function. Proteins are the major structural materials and are also involved in maintenance and regulation of life processes.

Some examples are shown in the table below

Protein type Examples FunctionStructural protein Keratin Protection of hairStructural protein Collagen and elastin Support for tendons and

ligamentsProtein hormones Insulin Glucose regulation

Enzymes Amylase Digestion of carbohydrates

Amino acids

Proteins are made from Amino Acids. Amino acids have two functional groups, the carboxyl group (-COOH) and the amine group (-NH2). The basic structure of all amino acids is shown below

All proteins contain carbon, nitrogen, oxygen and hydrogen.

The structure of some amino acids are shown below.

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Where R represents an arrangement of atoms. Different amino acids have different R groups.

Glycine

Alanine

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Amide (peptide) link


There are about 20 different amino acids in nature. With 20 different amino acids joining in large numbers, it is possible to produce a wide variety of protein molecules such as those found in skin, muscle, hair, fingernails and in enzymes (biological catalyst).

The body cannot make all the amino acids it requires and the ones we can’t make are called essential amino acids. They have to be taken in our diet. Examples of foods that are high in protein are meat, fish, cheese and eggs.

Proteins are specific to the body’s needs and are built up within the body by condensation reactions.

Making proteins

Proteins are condensation polymers made up of many amino acid molecules linked together.

The link which forms between the two amino acids is called an amide link. This can also be known as a peptide link.

This is an example of a condensation polymerisation reaction because many small amino acids join together with the release of water.

Breaking up proteins

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During digestion, insoluble proteins in food are hydrolysed into amino acids using enzymes.

These smaller molecules can be absorbed into the bloodstream and taken to the various parts of the body to be reassembled into a different order to give the proteins that we need.

Cooking Proteins

Within proteins, the long chains molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. These chains are held in these forms by intermolecular bonding between the side chains of the amino acids. These intermolecular bonds are hydrogen bonds. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature). These changes alter the texture of foods. of 47


For example, egg white (albumen) is changed from a clear liquid to a white solid during cooking. The protein in the egg white has been denatured. This means that the shape of the protein has changed.

Enzymes are proteins, and they will also be affected by changes in temperature and pH. Each enzyme has a specific shape which allows them to catalyse a specific reaction. When the enzyme has been denatured it can no longer catalyse that reaction.

Part 3 Oxidation of Foods and Chemistry of CookingOxidation of Foods

Foods contain many different chemicals. In this section we will look at how these substances react with oxygen and how this affects the taste and smell of the food. Alcoholic drinks and foods that contain alcohol can be oxidised. The products formed depends on the structure of the alcohol.

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OH

R’ C R H


Classification of Alcohols

Alcohols can be classified into 3 groups.

Primary Alcohols (1°) – the carbon atom attached to the hydroxyl group is bonded to no more than one other carbon (on an end carbon).

Ethanol

Secondary Alcohols (2°) – the carbon atom attached to the hydroxyl group is bonded to two other carbon atoms.

Propan-2-ol

Tertiary Alcohols (3°) – the carbon atom attached to the hydroxyl group is bonded to three other carbon atoms.

Oxidation of Alcohols

Complete oxidation of an organic compound is also known as combustion. When an alcohol is completely burned, carbon dioxide and water are produced.

CH3OH + 1 ½ O2 CO2 + 2 H2O of 47

H

R C OH

H

2-methylbutan-2-ol

OH

R’ C R

R’’

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Some organic compounds like alcohols can be mildly oxidised to produce different organic compounds.

Oxidising agents

In order to oxidise a primary or secondary alcohol an appropriate oxidising agent should be used. Commonly used oxidising agents are listed below.

Acidified potassium dichromate solution hot copper (II) oxide

The oxidising agents will be reduced as the alcohols are oxidised. Using acidified dichromate, the colour change is orange (Cr2O72- ) to green (Cr3+).

Cr2O72- + 14H+ + 6e- 2Cr3+ + 7H2O

Using copper oxide, the black colour of the copper (II) oxide changes to red-brown copper.

Cu 2+ + 2e Cu

ALDEHYDES AND KETONES

When a PRIMARY alcohol is oxidised the organic product produced in the oxidation step is called an ALDEHYDE. The ALKANALS are a homologous series of aldehydes.

When a SECONDARY alcohol is oxidised the organic product produced in the oxidation step is called an KETONE. The ALKANONES are a homologous series of ketones.

All aldehydes and ketones are called CARBONYL compounds because they contain the carbonyl group.

In aldehydes (alkanals), this group is always at the end of the molecule; in ketones (alkanones) the C=O always has 1 carbon attached at either side.

The first members of the homologous series of alkanals are :-

No of carbon

Name of alkanal

Full structural formula Chemical formula

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Oxidation can be The addition of oxygen The removal of

hydrogen An increase in O:H ratio

Reduction can be The removal of oxygen The addition of hydrogen A decrease in O:H ratio


1 methanal HCHO

2 ethanal CH3CHO

3 propanal C2H5CHO

4 butanal C3H7CHO

5 pentanal C4H9CHO

Nomenclature

When naming aldehydes, we don’t have to give the number of the carbonyl carbon as it is always carbon number 1.

The first members of the homologous series of alkanones are:-

No of carbon atoms

Name of alkanones

Full structural formula Chemical formula

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3 propanone CH3COCH3

4 butanone C2H5COCH3

5 pentanone C2H5COC2H5

Note : The first member of the alkanones must have 3 carbons (i.e. propanone) to fulfill the requirement of having at least 1 carbon on either side of the carbonyl group.

Nomenclature

When naming the ketones, the position of the C=O group is given in the name.

Reactions of aldehydes and ketones

When aldehydes and ketones are treated with mild oxidising agents such as acidified dichromate, Fehling’s solution or Tollen’s reagent only the ALDEHYDES react.

ALDEHYDES are oxidised to form CARBOXYLIC ACIDS

KETONES are not oxidised.

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Pentan-2-one

Pentan-3-one

3-methylpentan-2-one

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Aldehydes can be distinguished from ketones by experiment because of their different reactions with mild oxidising agents.Fehling’s solution contains blue Cu2+ ions which are reduced to orange Cu+ ions on reaction with aldehydes, but not with ketones.

Cu2+(aq) + e Cu+ (aq)

Tollen’s reagent contains Ag+ ions which are reduced to from a silver mirror of Ag atoms on reaction with aldehydes, but not with ketones.

Ag+(aq) + e Ag(s)

Oxidation Write up Sheet

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Summary of oxidation reactions of alcohols and carbonyl compounds

PRIMARY ALDEHYDE CARBOXYLIC ACID ALCOHOL (ALKANAL) (ALKANOIC ACID)

SECONDARY KETONE No further oxidation ALCOHOL (ALKANONE) TERTIARY Do not oxidise ALCOHOL

Reactions of Carboxylic Acids

The structure and naming of carboxylic acids was covered at the start of this unit.

Carboxylic acids can undergo the same type of chemical reactions as other laboratory acids, such as hydrochloric acid.

Metal hydroxides are bases. The H+ ion of the acid is replaced by the positive metal ion to form a salt and water.

HCl + NaOH NaCl + H20

Carboxylic acids form salts containing the carboxylate ion(-COO-).

When ethanoic acid reacts with sodium hydroxide a salt called sodium ethanoate is formed.

CH3COOH + NaOH NaCH3COO + H20

Propanoic acid would react with calcium hydroxide to form a salt called calcium propanoate.

2C2H5COOH + Ca(OH)2 Ca(C2H5COO)2 + 2H20

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Acid + Base Salt + Water


Other bases include: metal oxides, metal carbonates and ammonia eg..

Methanoic acid + lithium oxide lithium methanoate + water

2HCOOH + Li2O 2LiHCOO + 2H20

Ethanoic acid + copper(II) carbonate copper (II) ethanoate + water + carbon dioxide CH3COOH + CuCO3 Ca(CH3COO)2 + 2H20 + CO2

Propanoic acid + Ammonium hydroxide Ammonium propanoate + water

C2H5COOH + NH4OH NH4C2H5COO + H20

Carboxylic acids are produced by the oxidation of primary alcohols and aldehydes. In the reverse reaction carboxylic acids are reduced. This involves a decrease in the O:H ratio.

Aldehyde and ketone aromas

The aroma and flavour of one food or drink is rarely due to one molecule. Aldehydes and ketones are responsible for some of the aromas and flavours that familiar foods have.

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Carboxylic Acid Aldehyde Primary Alcohol

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Compound Name Structure Where found

Heptan-2-one Blue cheese

Furfural Coffee

2,3-butanedione Popcorn

Oxidation of aldehydes produces carboxylic acids. This alters the taste and smell of the food/drink.

Eg/ The ethanol in wine can oxides to ethanoic acid which tastes like vinegar.

Food preservation

PackagingManufacturers try to slow down the oxidation of food by packaging them in an inert atmosphere (eg nitrogen). However, once the food packaging has been opened the food quickly spoils as it is exposed to oxygen.

AntioxidantsAntioxidants are molecules that reduce the rate of oxidation reactions. Oxidation involves the loss of electron(s) to an oxidising agent. Ascorbic acid (vit C) is a

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natural antioxidant, as it readily losses electrons and saves the food from being oxidised. Ion-electron equations can be used to show how antioxidant molecules are oxidised.

C6H8O6 C6H6O6 + 2H+ + 2e-

Vitamin C DHA(ascorbic acid) (dehydroascorbic acid)

Vitamin C and its salts are added to soft drinks, jams, condensed milk and sausage to prevent oxidation.

Antioxidants can be natural or synthetic. Natural antioxidants tend to be short-lived and therefore synthetic antioxidants are used when a longer shelf-life is preferred.In reality, several antioxidants are often added in combination to foodstuffs to give the most effective action.

Examples of antioxidants are shown in the following table;

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Oxidation occurs when the apple is left exposed to air

The apple is protected when dipped in orange juice containing of high concentration of the antioxidant vitamin C


Oxidation of edible fats and oils

Foods which contain fats and oils are at a particularly high risk of oxidation. Oxygen from the air damages the structure of the edible fats or oils causing degradation of the long chain fatty-acids at the C=C. The oxidation of unsaturated oils and fats can lead to rancidity (rancidus [Latin] = stinking), which negatively affects both odour and taste, and has an impact on safety for human consumption.

Part 4 - Soaps, Detergents and Emulsions

Soaps

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Making Soaps. Soaps are formed by the alkaline hydrolysis (breaking up) of fats and oils by sodium or potassium hydroxide by boiling under reflux conditions. NaOH or KOH act as catalysts.

Antioxidant Natural/synthetic E number Types of food

Vitamin C(ascorbic acid)

Natural E300 Fruits, jams, vegetables

Vitamin E(tocopherols)

Natural E306 Oils, meat pies, soya

beans

Butylated hydroxyanisole

(BHA)

Synthetic E320 Margarine, cheese, crisps

http://en.wikipedia.org/wiki/File:Reflux_labled.svg


Hydrolysis of esters such as fats/oil produces glycerol and fatty acids.

Glycerol can be separated and used as a raw material for other processes and preparations for example:

Antifreeze (ethylene glycol). In food and beverages, glycerol serves as a humectant (keeps the food

moist), solvent, sweetener and emulsifier (see later). Glycerol is used to produce trinitroglycerin, which is an essential ingredient

of various explosives such as dynamite, gelignite.

Fatty acids formed react with the alkali to form a sodium or potassium salts (soaps) such as sodium stearate, C17H35COO-Na+ in a neutralisation reaction.

The soaps are ionic and water-soluble.

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http://en.wikipedia.org/wiki/Gelignite

http://en.wikipedia.org/wiki/Dynamite

http://en.wikipedia.org/wiki/Nitroglycerin

http://en.wikipedia.org/wiki/Sweetener

http://en.wikipedia.org/wiki/Solvent

http://en.wikipedia.org/wiki/Humectant


The long covalent hydrocarbon chain makes up the tail section of the soap structure. The charged carboxylate group (-COO-) represents the head section of the soap structure.

Why do we need soap or detergent to clean?Cleaning with water alone has little effect when stains consist of non-polar substances, such as fats, grease and sweat since they do not dissolve in water. This is because water is a polar solvent but fats and oils are non polar.In solution a soap molecule consists of a long non-polar hydrocarbon tail (e.g. C17H35) and a polar head (COO-).

The non-polar tail is soluble in non-polar substances such as oil while the polar head is soluble in polar substances such as water. As the non-polar tail is repelled by water, it is described as hydrophobic (water hating). The head is described as hydrophilic (water loving).

How soaps workAgitation of the oil and water produces oil droplets surrounded by negatively-charged heads and these repel similar charges on other oil droplets. The following ball and stick diagram represents the initial interaction of soap on addition to water and material with a grease stain.

This repulsion

prevents the oil droplets re-joining and helps disperse the oil.

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The structure of soap


Mechanism of stain/dirt removalRoll-up mechanism

The hydrophobic tails ‘burrow’ into the droplet of oil or grease.

The hydrophilic heads are left to face the surrounding water.

This results in the formation of a ball-like structure (a micelle).

The non-polar substances, such as oil or grease, are held inside the ball and suspended in water, to be washed away.Soapless detergents

When soap is used in hard water, a white precipitate called scum forms. This is because calcium and magnesium ions present in the hard water, react with the carboxolate ion in soap to form an insoluble substance. Scum reduces the cleaning action of the soap and builds up on clothes, baths and sinks.

In hard water areas it is best to use soapless detergents as they do not form scum. Like soap, the detergent molecules have a long hydrocarbon tail, which is oil soluble, but at the end of the molecule there is a sulphonate ion (-SO3 - ). Calcium and magnesium sulphonates are soluble and therefore don’t form a precipitate (scum).

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The calcium or magnesium salt of a sulphonate ion is soluble in water unlike the calcium or magnesium salts of the carboxylate ion.

Problems with Soapless Detergents.Soap molecules break up into smaller molecules containing carbon, hydrogen and oxygen atoms in the environment where they are taken up by plants and micro -organisms. Detergents break down in a similar way, but take much longer. This is why foam is sometimes seen on rivers and streams - the detergent molecules keep their properties much longer than soap.Although detergents are good at removing grease and dirt, they can also irritate and dry out the skin. Some people are sensitive to detergents and may have skin reactions when using them.

Emulsions An emulsion contains small droplets of one liquid dispersed in another liquid.

Mixture of oil and water - no emulsifer

In diagram A the two liquids form separate layers, a layer of oil on top of the water. In diagram B the liquids have been agitated (stirred vigorously), the water and oil layers have formed an emulsion.In diagram C the unstable emulsion progressively separates back into two distinct layers (phases).Eventually, after some minutes, the two liquids return to form two separate phases, a layer of oil on top of a layer of water, like diagram A.

Mixture of oil and water - with emulsifer

Diagram D shows what happens when an emulsifer is used stablise the emulsion.

Phase ll: Oil Phase I: Water

The addition of an emulsifier allows two immiscible layers to be mixed uniformly, dispersing an equal amount of each throughout the entire volume. The mixture is able to exist as a stable (non-separating) emulsion for a reasonable time (known as shelf-life). of 47

Phase ll: Oil Phase I: Water


Emulsifiers have a similar structure to soap and detergents in that they have hydrophobic tails and hydrophilic heads. They are made by reacting edible oils with glycerol. The molecules formed have either one or two fatty acid groups 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 emulsifiers are shown on food packaging. E-number E471 is one of the most common found on packaging. Many foods contain emulsifiers.

Foods that Commonly Contain Emulsifiers Biscuits Toffees BreadExtruded snacks Chewing gum Margarine / low fat spreadsBreakfast cereals Frozen desserts Coffee whitenersCakes Ice-cream Topping powdersDesserts / mousses Dried potato Peanut butter

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Emulsifiers - consumer productsIt is very important that we have a way of preventing the layers from separating, otherwise the majority of our consumer products, including shampoo, toothpaste, cosmetics, ice-cream, washing detergents and salad dressings, would all end up as seperated layers, with the active ingredients no longer able to work effectively.

Lecithin is an emulsifier found in egg yolks.

Mayonnaise is a mixture of vegetable oil and water or vinegar or lemon juice, depending on the recipe. Egg yolk or a synthetic emulsifier can be used to keep the normally immiscible liquids evenly mixed. Without the emulsifier the two liquids would separate and would not appear appetising.

http://www.google.co.uk/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=0CAgQjRw&url=http://www.agrofoodnews.com/Emulsifiers-in-food/news3665.html&ei=GZZaVPPxMLKBsQTFx4GoBw&psig=AFQjCNEFhhNMopLVXWwyit_m7Y_8mS4yrg&ust=1415309209977614


Soft drinks Chocolate coatings Caramels

Part 5 - Skincare and Fragrances

Essential OilsEssential oils are concentrated extracts of the aroma compounds from plants. The oils have the aroma of the plant from which they are extracted. They include lavender, peppermint, orange, lemon, and eucalyptus oils.

Uses of Essential Oils

They are mixtures of organic compounds rather than just one pure compound.

The word "essential" means derived or extracted from essences and is not the same as "essential" amino acids (which are vital as some living things cannot make them).

Essential oils are usually volatile (evaporate easily) and insoluble in water (hydrophobic).

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Essential oils

Cosmetics Flavours

Perfumes Medical

Cleaning

Insect repellents

Dentistry Adhesives


Steam Distillation

Essential oils can be extracted in the laboratory using the following apparatus.

Steam distillation is

one of the methods used to extract essential oils from plants. Steam passes over the plant and extracts the essential oil. The mixture evaporates and passes into the condenser. The essential oil vapour is cooled and collected. The essential oil collects as a mixture of oil and water which can be easily separated using a separating funnel.

Terpenes

The most common compounds found in essential oils are a family called terpenes.

Terpenes are found in a wide variety of fruit and floral flavours and aromas.

Structures of Terpenes

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Terpenes are unsaturated compounds formed by joining together isoprene (2-methylbuta-1,3-diene) units with the molecular formula C5H8.

2-methylbuta-1,3-diene


Isoprene units can be linked:

head to tail to form linear terpenes in rings to form cyclic terpenes.

Terpenes are based on the formula (C5H8)n, where n is the number of isoprene units joined together.

Limonene is a cyclic terpene found in the skin of citrus fruits.

10 carbon atoms = 2 isoprene unitsIt is known for its ability to act as a natural solvent and a cleanser.

Β-carotene is a linear terpene found in carrots.

40 carbon atoms = 8 isoprene unitsIt is used to colour foods and is a natural antioxidant found in supplements claiming to maintain health.

In nature, terpenes can be oxidised within plants producing some of the compounds responsible for the distinctive aroma of spices.

Common spices containing terpenes include cloves, cinnamon and ginger. Terpenes containing oxygen are known as ‘terpenoids'. of 47 This terpene has

been oxidised to a terpenoid


Peppermint oil is used for soothing digestion and improving the taste and smell of many products with its fresh, clean, minty aroma.

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menthol peppermint


Skin Care Products Effect of Ultraviolet Light

Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight.

UV light is divided into 3 groups UVA, UVB and UVC light.

UVA/B causes most damage to our skin. UVC light is the most dangerous but it does not penetrate the atmosphere

and so causes no problems.

Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken. This is the process responsible for sunburn (UVB) and also contributes to aging of the skin (UVA).

UV Photography reveals the effects of "photo-aging", or aging of skin caused by light. Photo-aging refers to the damage that is done to the skin from prolonged exposure to UV radiation, over a person's lifetime. Most of the skin changes that occur as we get older are accelerated by sun exposure. Examples of skin changes from photo-aging include dark spots, wrinkles, leathery skin and skin cancer (malignant melanoma).

UVA and UVB cause wrinkles by breaking down collagen, creating substances called free radicals, and inhibiting the natural repair of the skin.

Skin care products containing sun-blocks and sun screens can be used to reduce the damaging effect of UV light.

Sun screens contain chemicals which filter out some of the UV light so that less reaches the skin.

Sun-block products prevent UV light reaching the skin. e.g Titanium chloride found in some products reflect the light so that it does not reach the skin at all.

Free Radical Reactions

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When UV light breaks bonds free radicals are formed. Free radicals have unpaired electrons and, as a result, are highly reactive.

Hydrogen reacts explosively with chlorine in the presence of UV light. The reaction can be shown as follows:

H2(g) + Cl2(g) 2HCl(g)

This is a free radical chain reaction.

Free radical chain reactions include the following steps: initiation, propagation and termination.

Initiation

U.V. light provides the energy to break some Cl-Cl bonds to form two chlorine free radicals (atoms with an unpaired electron).

Cl2(g) Clo(g) + oCl(g)

Propagation

In this stage, the highly reactive chlorine free radicals collide with hydrogen molecules.

H2(g) + oCl(g) Ho (g) + HCl(g)

The hydrogen free radical produced can react with chlorine molecules.

Ho (g) + Cl2(g) HCl(g) + Clo(g)

These reactions continue until reactants are used up, or until free radicals are used up when they collide with each other.

Termination

In this stage, free radicals collide with each other to form stable molecules.

Ho(g) + oCl(g) HCl(g)Ho(g) + oH(g) H2(g)

Clo(g) + oCl(g) Cl2(g)

Reactions of Alkanes with Halogens

Alkanes slowly decolourise bromine water in the presence of UV light.

CH4(g) + Br2(g) CH3Br(g) + HBr(g)

The slow substitution reaction follows a three step free radical chain reaction.

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Initiation

U.V. light provides the energy to break some Br-Br bonds to form two bromine free radicals (atoms with an unpaired electron).

Br2(g) Bro (g) + oBr(g)

Propagation

Highly reactive bromine free radicals react with methane molecules

CH4(g) + oBr CH3o (g) + HBr(g)

The organic product of this reaction is known as a methyl radical. This reacts with bromine molecules.

CH3o (g) + Br2(g) CH3Br(g) + Bro (g)

These reactions continue until reactants are used up, or until free radicals are used up when they collide with each other.

Termination

In this stage, free radicals collide with each other to form stable molecules.

Bro (g) + oBr(g) Br2(g)CH3o (g) + oBr(g) CH3 - Br(g)

CH3o (g) + oCH3(g) CH3 - CH3(g)

Note -These are examples of photochemical reactions as they are initiated by U.V. light which provides the activation energy. Once started, they can continue in the dark.

Many chemicals are stored in brown glass bottles as this filters UV light which can cause the chemicals inside to break down.

Free-radical Scavengers

Many cosmetic products contain free radical scavengers. These are molecules which can react with free radicals to form stable molecules and prevent chain reactions.

As UV light can cause wrinkling of skin, some skin-care products claim to contain chemicals which prevent wrinkling. These are claimed to be anti-aging creams. Free radicals remove electrons from skin cells that damage them and cause wrinkles to develop.

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Melatonin, vitamin C and vitamin E are examples of natural free radical scavengers.

Free radical scavengers are:

added to food products to stop them from becoming rancid or discoloured. added to plastics to prevent them disintegrating on exposure to UV light.

Esters, Fats and Oils – Glossary

Word MeaningEster Link A group of atoms of formula -COO- found in ester molecules and

made from the combination of the carboxyl group and the alcohol group.

Condensation Reaction

A reaction where two or more molecules join together and a small molecule, usually water is eliminated.

Esterification A condensation reaction where an ester is made from an alcohol and carboxylic acid.

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Word MeaningReflux Where liquid evaporate to form gases which are then re-condensed

to continue reaction.

Non-Polar Describes a molecule where any charges are insignificant or absent. HydrolysisReaction

A reaction in which a molecule is broken into smaller molecules using water.

Vitamin A chemical needed in small amounts with an essential role in the body.

Glycerol The common name for the alcohol propane-1,2,3-triol found in fats and oils.

Fatty Acid A carboxylic acid with between 4 and 24 (but usually 16 or 18) carbon atoms in the molecule and found in fats and oils. Only even numbers of carbon atoms are found.

Trihydric Alcohol An alcohol with three hydroxyl (-OH) groups in one molecule.Triglyceride The chemical name for a fat or oil i.e. an ester of glycerol and three

fatty acid molecules.

Proteins – Glossary

Protein Naturally occurring compounds containing the elements carbon, hydrogen, oxygen and nitrogen.

Amino acid The constituent molecules which join together to form proteins.

Enzyme A biological catalyst which speeds up natural processes.Essential Amino Acids

Amino acids which are vital to the body but that can only be obtained from the diet.

Condensation Reaction

Amino acid molecules join together to from protein chains by eliminating molecules of water.

Amide Link A group of atoms, - CONH-, which joins amino acids in a protein. Sometimes called a peptide link.

Hydrolysis Reaction A reaction where a bond is broken in a molecule using water.Here, protein chains are broken down into the component amino acid molecule by adding water across the amide link.

Oxidation of Food and Chemistry of Cooking- Glossary

Alcohols Organic compounds containing the hydroxyl (-OH) group.

Primary (1°) Alcohols

Alcohols in which the hydroxyl is bonded to carbon which is bonded to no more than one other carbon.

Secondary (2°) Alcohols

Alcohols in which the hydroxyl is bonded to a carbon which is bonded to two other carbons.

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Tertiary (3°) Alcohols

Alcohols in which the hydroxyl is bonded to a carbon which is bonded to three other carbons.

Oxidation A reaction in which an organic compounds has the oxygen to hydrogen ratio increased. Oxygen can be added or hydrogen can be removed.

Reduction A reaction in which an organic compound has the oxygen to hydrogen ratio reduced. Oxygen can be removed or hydrogen can be added.

Carboxylic Acids Organic compounds containing the carboxyl (-COOH) group.

Aldehyde A compound which contains the -CHO group, carbonyl on the end carbon . .

Alkanals Aldehydes with have a structure based on an a straight chain alkane.

Ketone A compound which contains the >CO group, carbonyl on the middle carbon .

Alkanone Ketones with have a structure based on an a straight chain alkane.

Rancidity Deterioration of flavour and odour.

Antioxidants Molecules which donate an electron to free-radicals, preventing the deterioration of food.

Oxidising Agent A substance which causes oxidation of another substance and so undergoes reduction.

Soap, Detergents and Emulsions - Glossary

Soap The sodium or potassium salts of long chain fatty acids e.g. sodium stearate or potassium oleate.

Hydrophobic A substance which is repelled by water and so is insoluble in water. Literally - water hating.

Hydrophilic A substance which is attracted by water and so is soluble in water. Literally - water loving.

Miscible Describes two liquids which can dissolve completely so that only one layer exists e.g. ethanol and water are miscible

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Immiscible Describes liquids which separate into two layers, even after being mixed. e.g. oil and water are immiscible

Surfactant A material that can greatly reduce the surface tension of water when used in very low concentrations.

Emulsion A mixture of small droplets of one liquid such as oil dispersed in an another liquid such as water and kept there by an emulsifier.

Emulsifier A substance which will help maintain the mixing of two immiscible liquids into a relatively stable mixture called an emulsion.

Fragrances and Skincare - Glossary

Unsaturated Compounds contain at least one double (or triple) covalent bonds between carbon atoms e.g. alkenes such as ethene.

Solvent Extraction A method to separate compounds based on their relative solubilities in two different immiscible liquids.

Free Radical A reactive unit made when a covalent bond is broken and each fragment has an unpaired electron. Radicals can be atoms e.g. Ho or fragments of molecules such as a methyl radical, CH3o

Initiation The starting reaction of a chain reactionPropagation A stage in a chain reaction where the numbers of radicals is

maintained.Termination The last stage in a chain reaction, where all of the remaining

radicals are used up.Substitution A reaction where one atom is replaced by another atom.

Free Radical Scavenger

A molecule that can react with and remove free radicals.

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