Nature's Chemistry

Question 1

Saturated Compounds

Answer 1

Compounds containing only single carbon–carbon bonds are
described as saturated.

Question 2

Unsaturated Compounds

Answer 2

Compounds containing at least one carbon–carbon double bond
are described as unsaturated. Compounds containing carbon–
carbon double bonds can take part in addition reactions. In an
addition reaction, two molecules combine to form a single
molecule.

Question 3

Bromine Test

Answer 3

-It is possible to distinguish an unsaturated compound from a
saturated compound using bromine solution.
-Unsaturated compounds quickly decolourise bromine solution.
-To determine/compare which ester is a fat(saturated) or oil(unsaturated), add bromine solution until the first to decolourise which would be the oil because it’s more unsaturated

Question 4

Isomers:

Answer 4

Isomers:
-are compounds with the same molecular formula but different
structural formulae
-may belong to different homologous series
-usually have different physical properties

Question 5

The solubility, boiling point and volatility (ease of evaporation) of a
compound can be predicted by considering:

Answer 5

-the presence of O-H or N-H bonds, which implies hydrogen
bonding
-the spatial arrangement of polar covalent bonds which could
result in a molecule possessing a permanent dipole
-molecular size which would affect London dispersion forces
-the polarities of solute and solvent. Polar or ionic compounds
tend to be soluble in polar solvents, non-polar compounds tend
to be soluble in non-polar solvents

Question 6

Alcohol Definition

Answer 6

An alcohol is a molecule containing a hydroxyl functional group,
─OH group.

Question 7

Classification of Alcohols

Answer 7

-Alcohols can be classified as primary, secondary or tertiary.
-Alcohols containing two hydroxyl groups are called diols, and those
containing three hydroxyl groups are called triols.

Question 8

Hydroxyl group in alcohol

Answer 8

Hydroxyl groups make alcohols polar and this gives rise to
hydrogen bonding. Hydrogen bonding can be used to explain the
properties of alcohols, including boiling points, melting points,
viscosity and solubility/miscibility in water.

Question 9

Carboxylic Acids definition

Answer 9

A carboxylic acid is a molecule containing the carboxyl functional
group, ─COOH.

Question 10

Carboxylic Acid+Bases=

Answer 10

metal oxide + carboxylic acid = salt + water
metal hydroxide + carboxylic acid = salt + water
metal carbonate + carboxylic acid = a salt + water + carbon dioxide
-first name of the salt comes from the first name of the base
-second name of the salt comes from the acid used

Question 11

Ester

Answer 11

An ester is a molecule containing an ester link: ─COO─.

Question 12

Naming Esters

Answer 12

Esters can be named given the:
-names of their parent alcohol and carboxylic acid

Question 13

Esters Function

Answer 13

Esters are used as flavourings and fragrances as many have
pleasant, fruity smells. Esters are also used as solvents for nonpolar compounds that do not dissolve in water

Question 14

Formation of Esters/Condensation

Answer 14

-Esters are formed by a condensation reaction between an alcohol
and a carboxylic acid.
-In a condensation reaction, two molecules are joined together with
the elimination of a water.
-When an ester link is formed by the reaction between a hydroxyl
group and a carboxyl group, the small molecule eliminated is water
-concentrated sulphuric acid is the catalyst
-sodium carbonate is used to neutralises the sulphuric acid

Question 15

Breakdown of Esters/Hydrolysis

Answer 15

-Esters can be hydrolysed to produce an alcohol and a carboxylic
acid.
-In a hydrolysis reaction, a molecule reacts with water to break
down into smaller molecules.
-sodium hydroxide is the catalyst

Question 16

Edible Fats and Edible Oils

Answer 16

Edible fats and edible oils are esters formed from the condensation
of glycerol (propane-1,2,3-triol) and three carboxylic acid
molecules. The carboxylic acids are known as ‘fatty acids’ and can
be saturated or unsaturated straight-chain carboxylic acids, usually
with long chains of carbon atoms.

Question 17

Mp and Bp between oils and fats

Answer 17

Edible oils have lower melting points than edible fats.

Question 18

Oil molecule

Answer 18

Double bonds in oil(fatty acid) chains prevent oil molecules from
packing closely together, so the greater the number of double
bonds present, the weaker the van der Waals forces of attraction as there are less sights for LDF’s to occur.
The greater the degree of unsaturation, the lower the melting point.

Question 19

Fats and Oils

Answer 19

Fats and oils are naturally occurring esters of the alcohol glycerol and long chain carboxylic acids. (known as fatty acids)
-a concentrated source of energy
-essential for the transport and storage of fat-soluble vitamins in
the body

Question 20

Bromine test in Fats and Oils

Answer 20

Unsaturated compounds quickly decolourise bromine solution.
The bromine molecules add across the carbon–carbon double
bonds in an addition reaction. The greater the number of double
bonds present in a substance, the more bromine solution can be
decolourised.

Question 21

Melting and Boiling Points in Fats and Oils

Answer 21

Fat and oil molecules are roughly ‘tuning fork’ in shape with three limbs being hydrocarbon chains. If the chains are saturated, the molecules pack neatly together even at quite high temperatures. If the chains contain one or more double bonds the zig-zag chains become more distorted and the close packing of the molecules is less easy.
Fat-higher melting point(close packing strong LDF)
Oil-lower melting point(less packed weaker LDF)
-Fat molecules pack together tightly, making fats solid at room temperature.
-Double bonds in oil make them less compact
-less tightly packed molecules make oils liquid because the bonds between molecules are weaker

Question 22

Hydrolysis of Fats and Oils

Answer 22

-Fats and oils can also be hydrolysed to form fatty acids and glycerol. This is the reverse of condensation just likes breaking esters. This hydrolysis reaction provides the body with essential fatty acids such as linoleic and linolenic acid, which are essential for blood coagulation and brain development.
-Usually the fats and oils will be hydrolysed with a dilute solution of sodium hydroxide to make sodium salts of the fatty acids ( see chemistry of toiletries later)

Question 23

Hardening Oils

Answer 23

Remember the more saturated the fat or oil, the more solid it is. The key to converting liquid oil into a solid fat is to reduce the degree of unsaturation.
Reducing unsaturation means getting rid of some of the double bonds in the fatty acid sections of the ester molecules. Hydrogen molecules need to be added across these double bonds to reduce them to single bonds.

From Nat 5, the process of adding hydrogen is called hydrogenation and it is carried out using a catalyst, often nickel.
Hardening a fat or oil means hydrogenating it to increase its melting point.
When margarine is manufactured from vegetable oils, such as sunflower seed oil and olive oil, the extent of hydrogenation is carefully controlled. If the product were totally saturated it would be too hard to spread easily when taken straight from the fridge as well as again being unhealthy. If it were too unsaturated, it would be too runny at room temperature.

Question 24

Soaps definition

Answer 24

Soaps are produced by the alkaline hydrolysis of edible fats and
edible oils. Hydrolysis produces three fatty acid molecules and one
glycerol molecule. The fatty acid molecules are neutralised by the
alkali, forming water-soluble ionic salts called soap

Question 25

Function of Soaps

Answer 25

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

Question 26

Hard Water

Answer 26

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.

Question 27

Soapless Detergents

Answer 27

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.

Question 28

Emulsifier definition

Answer 28

An emulsifier can be used to prevent non-polar and polar liquids
separating into layers.

Question 29

Emulsion definition

Answer 29

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

Question 30

Formation of Emulsifier

Answer 30

Emulsifiers for use in food can be made by reacting edible oils with
glycerol. In the molecules formed, only one or two fatty acid groups
are linked to each glycerol backbone. The hydroxyl groups present
in the emulsifier are hydrophilic whilst the fatty acid chains are
hydrophobic. The hydrophobic fatty acid chains dissolve in oil whilst
the hydrophilic hydroxyl groups dissolve in water, forming a stable
emulsion.

Question 31

Proteins Definition

Answer 31

-Proteins are the major structural materials of animal tissue and are
also involved in the maintenance and regulation of life processes
-Proteins which fulfil different roles in the body are formed by linking
together differing sequences of amino acids.

Question 32

Enzymes

Answer 32

Enzymes are proteins which act as biological catalysts

Question 33

Amino Acids

Answer 33

-Amino acids, the building blocks from which proteins are formed,
are relatively small molecules which all contain an amino group,
—NH2, and a carboxyl group, —COOH.
-The body cannot make all of the amino acids required for protein
synthesis and certain amino acids, known as essential amino acids,
must be acquired from the diet.

Question 34

Formation of Proteins

Answer 34

Proteins are made of many amino acid molecules linked together
by condensation reactions. In these reactions, the amino group of
one amino acid and the carboxyl group of another amino acid join,
with the elimination of water.

Question 35

Link between amino acids

Answer 35

The link which forms between two amino acids is known as a
peptide link, —CONH—, or also as an amide link.

Question 36

Digestion/Amino Acids

Answer 36

During digestion, enzyme hydrolysis of protein produces amino
acids.
-The structural formulae of amino acids obtained from the hydrolysis
of a protein can be drawn given the structure of a section of the
protein.
-The structural formula of a section of protein can be drawn given
the structural formulae of the amino acids from which it is formed.

Question 37

Denaturing of Proteins

Answer 37

Within proteins, the long-chain molecules form spirals, sheets, or
other complex shapes. The chains are held in these forms by
intermolecular bonding between the side chains of the constituent
amino acids. When proteins are heated, these intermolecular
bonds are broken, allowing the proteins to change shape
(denature). The denaturing of proteins in foods causes the texture
to change when it is cooked.

Question 38

Oxidation of food

Answer 38

For carbon compounds:
-oxidation is an increase in the oxygen to hydrogen ratio(more oxygen)
-reduction is a decrease in the oxygen to hydrogen ratio(more hydrogen)
-Oxygen from the air causes the oxidation of food. The oxidation of
edible oils gives food a rancid flavour.

Question 39

Oxidation of food pt.2

Answer 39

-Hot copper(II) oxide or acidified dichromate(VI) solutions can be
used to oxidise:
-primary alcohols to aldehydes and then to carboxylic acids
-secondary alcohols to ketones
-During these reactions black copper(II) oxide forms a brown solid,
and orange dichromate solution turns green.
Tertiary alcohols cannot be oxidised using these oxidising agents.

Question 40

Aldehydes and Ketones

Answer 40

Aldehydes and ketones are molecules containing a carbonyl
functional group
C=O

Question 41

Aldehydes

Answer 41

Aldehydes, but not ketones, can be oxidised to carboxylic acids.
Oxidising agents can be used to differentiate between an aldehyde
and a ketone. With an aldehyde:
-blue Fehling’s solution forms a brick red precipitate
-clear, colourless Tollens’ reagent forms a silver mirror
-orange acidified dichromate solution turns green

Question 42

Aldehyde funtion

Answer 42

Many flavour and aroma molecules are aldehydes.

Question 43

Antioxidants

Answer 43

Antioxidants:
-are molecules that prevent unwanted oxidation reactions
occurring
-are substances that are easily oxidised, and oxidise in place of
the compounds they have been added to protect
-can be identified as the substance being oxidised in a redox
equation

Question 44

Essential Oils

Answer 44

Essential oils are concentrated extracts of the volatile, non-watersoluble aroma compounds from plants. They are mixtures of many
different compounds. They are widely used in perfumes, cosmetic
products, cleaning products and as flavourings in foods.

Question 45

Terpenes

Answer 45

Terpenes are key components in most essential oils. They are
unsaturated compounds formed by joining together isoprene (2-
methylbuta-1,3-diene) units.

Question 46

Oxidation of terpenes

Answer 46

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

Question 47

Given the structural formula for a terpene-based molecule

Answer 47

-an isoprene unit can be identified within the molecule
-the number of isoprene units joined together within the
molecule can be stated(carbon number can be divided by 5)

Question 48

UV

Answer 48

Ultraviolet radiation (UV) is a high-energy form of light, present in
sunlight. UV light can provide sufficient energy to break bonds
within molecules. This causes sunburn and accelerates ageing of
the skin. Sun-block products prevent UV light reaching the skin.

Question 49

Free Radicals

Answer 49

-When UV light breaks bonds, free radicals are formed. Free
radicals are atoms or molecules that are highly reactive due to the
presence of unpaired electron
-Free radical chain reactions include the following steps: initiation,
propagation and termination.

Question 50

Free Radical Scavengers

Answer 50

Free radical scavengers are molecules that react with free radicals
to form stable molecules and prevent chain reactions from
occurring. Free radical scavengers are added to many products
including cosmetics, food products and plastics.

Question 51

Classification of fatty acids

Answer 51

-If the number of hydrogens is = or less than double the number of carbons Cn H<2n = unsaturated
-If the number of hydrogens is more than double the number of carbons Cn H>2n = saturated