Chemistry Of Cooking

Question 1

What does a person sense of taste come form?

Answer 1

A combination of sensors on the tongue and also their sense of smell

Question 2

What do many of the chemical compounds that give foods their flavour contain? And what does this mean?

Answer 2

Weak intermolecular forces. Due to this such chemicals are volatile molecules e.g. Aldehydes

Question 3

How do different cooking methods alter the flavour of foods?

Answer 3

By affecting the chemical compounds responsible for flavour

Question 4

What are the sources of flavour and aroma in our food? 2

Answer 4

Aldehydes or ketones

Question 5

During cooking what happens to volatile molecules?

Answer 5

Leave the food and enter the air
Or
Dissolve in the cooking liquid

Question 6

Why is the method of cooking important?

Answer 6

To preserve flavour

Question 7

What is the best of method to cook some foods?

Answer 7

If polar cook in a substance which is non polar such as butter or oil
If non polar cook in a substance which is polar such as water

Question 8

What makes collagen tough in texture?

Answer 8

The protein chains form a rope-like structure with hydrogen bonds between chains

Question 9

When meat is cooked what happens?

Answer 9

the hydrogen bonds that holds the protein chains together are broken. This causes the protein chains to unravel and changes the texture of the meat.

Question 10

As a protein is heated, the intermolecular bonds are broken. As a result what happens to the shape of the protein and what is the protein said to be?

Answer 10

the shape of the protein changes and the protein is said to be denatured.

Question 11

How is soap made?

Answer 11

By heating fats or oils with an alkali (NaOH). This reaction is called saponification. The fat or oil is hydrolysed to glycerol and ionic salts of fatty acids

Question 12

What are the ionic salts of these fatty acids?

Answer 12

the actual soap

Question 13

What are the 2 types of bonding soap molecules have?

Answer 13

an ionic carboxylate head (negatively charged) and a covalent tail

Question 14

What is the non-polar covalent tail described to be?

Answer 14

hydrophobic

Question 15

What is the ionic head described to be?

Answer 15

hydrophilic

Question 16

Describe what happens when a salt is mixed with grease/ oil and what happens when it is mixed with water?

Answer 16

When mixed with grease or oil, the non-polar end dissolves in oil and grease (like dissolves in like).

The ionic end of the molecules dissolves in water (polar).

Question 17

What does agitation result in?

Answer 17

a ball-like structure forming with the hydrophobic tail on the inside and negative hydrophilic head on the outside

Question 18

What does repulsion between these negative charges of the soap head result in?

Answer 18

an emulsion being formed and the dirt released

Question 19

What does ‘hard water’ mean?

Answer 19

the water contains dissolved calcium and magnesium ions

Question 20

What happens when hard water is mixed with soap?

Answer 20

a precipitate called a ‘‘scum’’ is formed rather than a latter.

Question 21

The scum that forms reduces the effectiveness of the soap to clean. How could we overcome this problem?

Answer 21

by using soapless detergents which will not form a scum with the hard water

Question 22

Where are detergents found?

Answer 22

In many household cleaners e.g. washing powders and washing-up liquids

Question 23

Give an example of a soapless detergent?

Answer 23

dodecylbenzenesulfonate

Question 24

What does dodecylbenzenesulfonate have that makes it similar to soap?

Answer 24

A non polar tail and an ionic head

Question 25

What makes dodecylbenzenesulfonate different from soap apart from the benzene ring?

Answer 25

It will not react with calcium or magnesium to form a precipitate I.e. Scum

Question 26

What is the simplest aromatic compound?

Answer 26

Benzene

Question 27

Benzene doesn’t react with bromine water. What can this indicate about its structure?

Answer 27

It doesn’t have c=c bonds

Question 28

What does the circle in the benzene ring indicate?

Answer 28

Delocalised electrons

Question 29

What is an emulsion?

Answer 29

A liquid which contains small droplets of one liquid dispersed in another liquid (e.g. Oil and water mixture)

Question 30

Grease and water would normally separate into two layers? How could these substances be brought together?

Answer 30

Soap can be added to act like an emulsifier

Question 31

What are emulsifiers present in?

Answer 31

A large range of foods such as mayo is an emulsion of olive oil and vinegar. Egg yolk acts as an emulsifier in this instance

Question 32

How are emulsifiers used in food normally made?

Answer 32

Reacting edible oils with glycerol. This leaves one or two fatty acid molecules linked with a glycerol backbone

Question 33

What is the long fatty acid chains said to be?

Answer 33

Non polar and hydrophobic

Question 34

What are the hydroxyl groups said to be?

Answer 34

Polar and hydrophilic

Question 35

In the case of vinegar and oil describe what would happen if an emulsifier was added?

Answer 35

The nonpolar fatty acid part of the emulsifier is attracted to the oil
The polar hydroxyl part of the emulsifier is attracted to the vinegar
The emulsifier acts like a soap as it is capable of dissolving both nonpolar and polar substances