2.7 oxidation of food

Question 1

What is oxidation in a carbon compound?

Answer 1

increase on the oxygen to hydrogen ratio

Question 2

what is reduction in a carbon compound?

Answer 2

decrease in the oxygen to hydrogen ratio

Question 3

What can hot copper(II) oxide or acidified dichromate(VI) solutions be used to oxidise?

Answer 3

• primary alcohols->aldehydes->carboxylic acids

- secondary alcohols-> ketones

Question 4

What happens to hot copper(II) oxide and dichromate (VI) solutions when oxidising primary and secondary alcohols?

Answer 4

copper(II)oxide
-black->brown solid
dichromate(VI)solution
-orange->green

Question 5

explain the use of hot copper(II) oxide and dichromate (VI) solutions on tertiary alcohols

Answer 5

• tertiary alcohols are not readily oxidised

- they cannot be oxidised using these oxidation agents

Question 6

What is the functional group in aldehydes and keynotes?

Answer 6

carbonyl >C=O

Question 7

what happens to aldehydes when oxidised?

Answer 7

oxidised to carboxylic acids

Question 8

what happened to ketones when oxidised?

Answer 8

they can’t be oxidised to carboxylic acids. They are not readily oxidised

Question 9

What is the reaction of blue Fehling’s solution with an aldehyde?

Answer 9

-brick red precipitate

Question 10

what is the reaction of Tollens’ solution with an aldehyde?

Answer 10

-colourless/clear–>silver mirror

Question 11

what is the reaction of acidified dichromate solution when there is an aldehyde present?

Answer 11

-orange->green

Question 12

What causes the oxidation of food?

Answer 12

oxygen in the air

Question 13

What happens when edible oils are oxidised

Answer 13

it gives food a rancid flavour

Question 14

What are antioxidants?

Answer 14

-molecules that prevent unwanted oxidation reactions occurring
-substances that are easily oxidised
-oxidise in place of the compounds they have been added to protect
-they can be identified as the substance being oxidised in a redox equation
(preserving flavour in foods)

Question 15

How do antioxidants work?

Answer 15

-they are substances that are easily oxidised, they oxidise in place of the compounds they haven been added to protect

Question 16

What is the difference between and aldehyde and a ketone?

Answer 16

the carbonyl functional group is on an end carbon in an aldehyde and an intermediate carbon in a ketone.

Question 17

What is an isomer?

Answer 17

compounds with the same molecular formula but different structural formula

Question 18

What 3 oxidising agents can be used to differentiate between and aldehyde and a ketone?

Answer 18

• acidified potassium dichromate solution
• Fehling’s solution
• Tollens’ reagent

Question 19

What can aldehydes be used for?

Answer 19

flavour and aroma molecules

Question 20

What is produced when primary alcohols are oxidised?

Answer 20

aldehydes

Question 21

What is produced when secondary alcohols are oxidised?

Answer 21

ketones

Question 22

What is produced when aldehydes are oxidised?

Answer 22

carboxylic acids

Question 23

What are 3 oxidising agents used to distinguish between aldehydes and ketones?

Answer 23

• acidified potassium dichromate solution
• Fehling’s solution
• Tollens’ reagent

Question 24

describe the reduction of carboxylic acids

Answer 24

carboxylic acid–>aldehyde–>primary alcohol

Question 25

Explain how different cooking methods can alter the flavour and nutritional value of foods?

Answer 25

- polar groups are soluble in water - if the vitamin is polar then cooking the food in water will remove the vitamin value from the food - non-polar groups do not dissolve in water and therefore by cooking non-polar molecules in water, the molecules do not dissolve

Question 26

What functional groups are polar?

Answer 26

- OH - C=O - COOH - NH2 - CONH

Question 27

What happens when aldehydes are oxidised in foods?

Answer 27

they produce carboxylic acids | -the food becomes spoiled and can have a very acidic taste (due to the carboxylic acids)

Question 28

How do food manufactures prevent oxidation of foods?

Answer 28

- packages in an atmosphere of nitrogen | - addition of antioxidants

Question 29

What are flavour and aroma molecules in food often?

Answer 29

aldehydes and ketones

Question 30

What is the volatility of a flavour compound determined by?

Answer 30

its structure