Unit 2

Question 1

How can you differentiate an ester?

Answer 1

• Esters have characteristic smells and are used as flavourings and fragrances.
• Esters are also used as industrial solvents.

Question 2

What happens in a condensation reaction

Answer 2

In condensation reactions, the molecules join together with the elimination of a small stable molecule

Question 3

Why do oils have lower M.P than fats?

Answer 3

• The lower melting points of oils compared to those of fats is related to the higher degree of unsaturation of oil molecules.
• The low melting points of oils are a result of the effect that the shapes of the molecules have on close packing, hence on the strength of van der Waals’ forces of attraction.

Question 4

What are fats and oils useful for?

Answer 4

Fats and oils are:

• a concentrated source of energy
• essential for the transport and storage of fat- soluble vitamins in the body

Question 5

What are amino acids?

Answer 5

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).

Question 6

How are proteins formed

Answer 6

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

Question 7

What are essential amino acids?

Answer 7

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

Question 8

What happens in digestion to proteins?

Answer 8

• During digestion, enzyme hydrolysis of dietary proteins can produce amino acids.
• The structural formulae of amino acids obtained from the hydrolysis of proteins can be identified from the structure of a section of the protein.

Question 9

How are proteins structures?

Answer 9

• Within proteins, the long-chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes.
• The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids.

Question 10

What happens when proteins are heated?

Answer 10

• 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.

Question 11

Do aldehydes and ketones oxidise?

Answer 11

• Aldehydes, but not ketones, can be oxidised to carboxylic acids.
• Fehling’s solution, Tollens’ reagent and acidified dichromate solution can be used to differentiate between an aldehyde and a ketone.

Question 12

If Tollens reagent, Fehling’s solution or acidified potassium dichromate are used, if it is a positive test what is witnessed?

Answer 12

Positive test results:

• Fehling’s — blue solution to a brick red precipitate
• Tollens’ — formation of a silver mirror
• acidified dichromate test — colour change from orange to green

Question 13

What can be used to oxidise primary/secondary alcohols

Answer 13

In the laboratory, hot copper(II) oxide or acidified dichromate(VI) solutions can be used to oxidise primary and secondary alcohols

Question 14

In carbon compounds, how can oxidation be spotted

Answer 14

When applied to carbon compounds, oxidation results in an increase in the oxygen to hydrogen ratio and reduction results in a decrease in the oxygen to hydrogen ratio.

Question 15

What happens when oxygen reacts with edible oils?

Answer 15

• Oxygen reacts with edible oils giving the food a rancid flavour.
• Antioxidants are molecules which will prevent these oxidation reactions taking place.

Question 16

What happens in alkaline hydrolysis of fats/oils

Answer 16

Production of soaps by the alkaline hydrolysis of fats and oils to form water-soluble ionic salts called soaps.

Question 17

Structure of soap ions?

Answer 17

Soap ions have a long covalent tail, readily soluble in covalent compounds (hydrophobic), and an ionic carboxylate head which is negatively charged and water soluble (hydrophilic).

Question 18

What happens when cleaning with soap?

Answer 18

• During cleaning using soaps the hydrophobic tails dissolve in a droplet of oil or grease, whilst the hydrophilic heads face out into the surrounding water.
• Agitation of the mixture results in ball-like structure forming with the hydrophobic tails on the inside and the negative hydrophilic head on the outside.
• Repulsion between these negative charges results in an emulsion being formed and the dirt released.

Question 19

What happens when using detergents?

Answer 19

• When using detergents: the hydrophobic tails dissolve in a droplet of oil or grease, whilst the hydrophilic heads face out into the surrounding water.
• Agitation of the mixture results in ball-like structure forming with the hydrophobic tails on the inside and the hydrophilic head on the outside.

Question 20

How are emulsifiers made

Answer 20

• 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.

Question 21

What are essential oils?

Answer 21

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

Question 22

What are terpenes?

Answer 22

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

Question 23

What happens when terpenes oxidise

Answer 23

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

Question 24

What is UV light and what does it do

Answer 24

• Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight.
• Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken.
• This is the process responsible for sunburn and also contributes to aging of the skin.
• Sun-block products prevent UV light reaching the skin.

Question 25

What are free radicals and how are they formed

Answer 25

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

Question 26

Why do many cosmetic products contain free radical scavengers

Answer 26

• Many cosmetic products contain free radical scavengers; molecules which can react with free radicals to form stable molecules and prevent chain reactions.
• Free radical scavengers are also added to food products and to plastics.