Nature's Chemistry

Question 1

What sort of compound can be described as saturated?

Answer 1

A compound containing only single carbon–carbon bonds.

Question 2

What sort of compound can be described as unsaturated?

Answer 2

A compound containing at least one carbon–carbon double bond.

Question 3

What type of compound can take part in an addition reaction?

Answer 3

Compounds containing carbon–carbon double bonds.

Question 4

What happens in an addition reaction?

Answer 4

Two molecules combine to form a single molecule.

Question 5

How is it possible to distinguish an unsaturated compound from a saturated compound?

Answer 5

Unsaturated compounds quickly decolourise bromine solution.

Question 6

What are isomers?

Answer 6

Compounds with the same molecular formula but different structural formulae.

Question 7

The solubility, boiling point and volatility (ease of evaporation) of a compound can be predicted by considering which 4 things?

Answer 7

• the presence of O-H or N-H bonds
• the spatial arrangement of polar covalent bonds
• molecular size
• the polarities of solute and solvent

Question 8

What is the general rule regarding solubility in relation to polarity?

Answer 8

Like dissolves like.

Question 9

What is an alcohol?

Answer 9

A molecule containing a hydroxyl (OH) functional group.

Question 10

What do you call alcohols containing two hydroxyl groups?

Answer 10

Diols.

Question 11

What do you call alcohols containing three hydroxyl groups?

Answer 11

Triols.

Question 12

What is a carboxylic acid?

Answer 12

A molecule containing a carboxyl (COOH) functional group.

Question 13

What do you get when you react a metal oxide and a carboxylic acid?

Answer 13

A salt and water.

Question 14

What do you get when you react a metal hydroxide and a carboxylic acid?

Answer 14

A salt and water.

Question 15

What do you get when you react a metal carbonate and a carboxylic acid?

Answer 15

A salt, water and carbon dioxide.

Question 16

What is an ester?

Answer 16

A molecule containing an ester link (-COO-).

Question 17

What are some uses of esters?

Answer 17

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

Question 18

How are esters formed?

Answer 18

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

Question 19

What happens in a condensation reaction?

Answer 19

Two molecules are joined together with the elimination of a small molecule.

Question 20

Which small molecule is eliminated in the condensation reaction between an alcohol and a carboxylic acid to make an ester?

Answer 20

Water.

Question 21

What happens in a hydrolysis reaction?

Answer 21

A molecule reacts with water to break down into smaller molecules.

Question 22

What is another name for glycerol?

Answer 22

Propane-1,2,3-triol.

Question 23

The condensation of which molecules forms edible fats and oils?

Answer 23

Glycerol and three carboxylic acid molecules.

Question 24

Edible fats and oils are types of which molecule?

Answer 24

Esters.

Question 25

why do edible oils have lower melting points than edible fats?

Answer 25

Edible oils contain a greater number of carbon-carbon double bonds and therefore the chains cannot pack closely together so there are fewer Van Der Waal’s forces present and the melting point is lower.

Question 26

Why do unsaturated compounds decolourise bromine solution?

Answer 26

The bromine molecules add across the carbon–carbon double bonds in an addition reaction.

Question 27

why are fats and oils important to the human body?

Answer 27

• they are a concentrated source of energy

- they are essential for the transport and storage of fat-soluble vitamins in the body

Question 28

How are soaps produced?

Answer 28

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 soaps.

Question 29

What are soaps used for?

Answer 29

The removal of non-polar substances such as oil and grease.

Question 30

How do soaps remove grease?

Answer 30

Soap ions have long non-polar tails and ionic heads that are water-soluble. The hydrophobic tails dissolve in the oil or grease. The negatively-charged 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 31

What is hard water?

Answer 31

Water containing high levels of dissolved metal ions. When soap is used in hard water, scum, an insoluble precipitate, is formed.

Question 32

What are soapless detergents?

Answer 32

Substances with non-polar hydrophobic tails and ionic hydrophilic heads. These remove oil and grease in the same way as soap

Question 33

What can be used to prevent non-polar and polar liquids separating into layers?

Answer 33

An emulsifier.

Question 34

What is an emulsion?

Answer 34

A substance which contains small droplets of one liquid dispersed in another liquid.

Question 35

Emulsifiers for use in food can be made by reacting which 2 substances?

Answer 35

Edible oils and glycerol.

Question 36

How do emulsifiers work?

Answer 36

Only one or two fatty acid groups are linked to each glycerol backbone of the emulsifier. 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 37

What do proteins do?

Answer 37

Proteins are the major structural materials of animal tissue and are also involved in the maintenance and regulation of life processes.

Question 38

What are enzymes?

Answer 38

Proteins which act as biological catalysts.

Question 39

What are amino acids?

Answer 39

The building blocks from which proteins are formed. They are relatively small molecules which all contain an amino group, —NH2, and a carboxyl group, —COOH.

Question 40

What kind of reaction joins together amino acids to make proteins and what happens in them?

Answer 40

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 41

What joins together amino acids in a protein?

Answer 41

Peptide or amide links (-CONH-).

Question 42

What are essential amino acids?

Answer 42

Amino acids which the body cannot make and which must be acquired through diet.

Question 43

What process produces amino acids during digestion?

Answer 43

Enzyme hydrolysis of protein.

Question 44

What causes high-protein foods to change texture when cooked?

Answer 44

The denaturing of proteins.

Question 45

Which 2 substances can act as oxidising agents for alcohols?

Answer 45

Hot copper(II) oxide or acidified dichromate(VI) solutions.

Question 46

What do you get when you oxidise a primary alcohol?

Answer 46

An aldehyde.

Question 47

What do you get when you oxidise an aldehyde?

Answer 47

A carboxylic acid.

Question 48

What do you get when you oxidise a secondary alcohol?

Answer 48

A ketone.

Question 49

What do you get when you oxidise a tertiary alcohol?

Answer 49

Absolutely nothing.

Question 50

Which functional group do both aldehydes and ketones contain?

Answer 50

The carbonyl group.

Question 51

Which 3 substances react with aldehydes but not with ketones?

Answer 51

• blue Fehling’s solution (forms a brick red precipitate)
• clear, colourless Tollens’ reagent (forms a silver mirror)
• orange acidified dichromate solution (turns green)

Question 52

What gives food a rancid flavour?

Answer 52

The oxidation of edible oils.

Question 53

What are antioxidants?

Answer 53

Molecules that prevent unwanted oxidation reactions occurring.

Question 54

How do antioxidants work?

Answer 54

They are easily oxidised, and oxidise in place of the compounds they have been added to protect.

Question 55

What are essential oils?

Answer 55

Concentrated extracts of the volatile, non-water soluble aroma compounds from plants.

Question 56

What are essential oils used in?

Answer 56

Perfumes, cosmetic products, cleaning products and as flavourings in foods.

Question 57

What are terpenes?

Answer 57

They are unsaturated compounds

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

Question 58

What is UV radiation?

Answer 58

A high-energy form of light, present in sunlight.

Question 59

How does UV radiation cause sunburn?

Answer 59

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 60

What are free radicals?

Answer 60

Atoms or molecules that are highly reactive due to the presence of unpaired electrons. They are formed when UV light breaks bonds.

Question 61

What are the 3 steps in free radical chain reactions?

Answer 61

Initiation, propagation and termination.

Question 62

What are free radical scavengers?

Answer 62

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.