Oxidation and Chemistry of Cooking

Question 1

How are alcohols classified into types and describe the classifying feature of each?

Answer 1

Classified by the position of the hydroxyl group
Primary - -OH group bonded to carbon with only one other carbon attached, ie at end of chain
Secondary - OH group to carbon with two carbons attached, i.e an intermediate carbon.
Tertiary - OH group bonded to carbon with three carbons attached, i.e an intermediate carbon with a branch.

Question 2

Describe the oxidation of a primary alcohol.

Answer 2

Primary alcohol - aldehyde - carboxylic acid

Question 3

Describe the oxidation of a secondary alcohol.

Answer 3

Secondary alcohol - ketone

Question 4

Describe the oxidation of a tertiary alcohol.

Answer 4

Not readily oxidised

Question 5

What are the suitable oxidising agents for the oxidation of an alcohol?

Answer 5

Acidified potassium dichromate and Copper (II) Oxide

Question 6

What is the colour change observed when acidified potassium dichromate is used as oxidising agent?

Answer 6

orange - blue/green

Question 7

Describe the experimental procedure for oxidation of an alcohol with a mild oxidising agent e.g acidified dichromate

Answer 7

alcohol placed in test tube with oxidising agent and test tube placed in hot water bath

Question 8

How can aldehydes and ketones be identified?

Answer 8

The presence of the carbonyl group, C to O double bond

Question 9

Where is the carbonyl group in a aldehyde?

Answer 9

The end of the carbon chain.

Question 10

Where is the carbonyl group in a ketone?

Answer 10

An intermediate carbon.

Question 11

What is the ending given to a ketone?

Answer 11

-one

Question 12

What is the ending given to a aldehyde?

Answer 12

-al

Question 13

What kind of chemical used to distinguish between aldehydes and ketones?

Answer 13

An oxidising agent, since aldehydes oxidise to carboxylic acids and ketones do not readily oxidise.

Question 14

What are suitable oxidising agents for distinguishing between aldehydes and ketones? And what colour change is observed?

Answer 14

Fehling’s solution - blue -> orange/red
Tollen’s reagent - colourless -> silver mirror
Acidified potassium dichromate - orange ->green/blue

Question 15

What is oxidation (carbon compounds)

Answer 15

A increase in the oxygen - Hydrogen ratio

Question 16

What is reduction (carbon compounds)

Answer 16

A decrease in the O:H ratio

Question 17

What is produced when carboxylic acids are reduced?

Answer 17

Carboxylic acid - aldehyde - primary alcohol.

Question 18

Why are carboxylic acids known as weak acids?

Answer 18

They produce H+ ions when added to water, but not to the same extent as strong acids

Question 19

What is produced when a carboxylic acid is reacted with a base?

Answer 19

Salts which contain the carboxylate ion (COO-) and water

Question 20

What are salts of carboxylic acids used for?

Answer 20

Preservatives in the food industry

Question 21

What kind of molecules are many aroma and flavour molecules?

Answer 21

Aldehydes and Ketones

Question 22

What reaction causes food to spoil?

Answer 22

Oxidation

Question 23

What is added to foods to prevent it spoiling?

Answer 23

Antioxidants.

Question 24

What happens when edible oils are oxidised?

Answer 24

They develop a rancid flavour

Question 25

What affects the method of cooking for foods?

Answer 25

The polarity of the flavour molecules

Question 26

What chemical change occurs when a protein is heated?

Answer 26

Denaturing

Question 27

What is the denaturing of a protein?

Answer 27

The permanent change in structure of the protein

Question 28

What change occurs in meat when cooked?

Answer 28

The protein collagen and other proteins are denatured, making the meat more palatable.

Question 29

What property can be predicted by examination of the size and structure of a molecule?

Answer 29

Volatility.