Alcohols and Oxidation of Alcohols

Question 1

what are the 3 types of alcohols

Answer 1

primary, secondary and tertiary

Question 2

what does R mean?

Answer 2

repeating carbon chain

Question 3

position of OH in primary alcohol

Answer 3

joined to the end of a carbon chain (attached to carbon with 1 other carbon bonded

Question 4

position of OH in secondary alcohol

Answer 4

joined to an intermediate carbon atom (attached to a carbon with 2 other carbons bonded)

Question 5

position of OH in tertiary alcohol

Answer 5

joined to an intermediate carbon which also has a branch attached (attached to a carbon with 3 other carbons bonded)

Question 6

alternative definition of oxidation (not loss of electrons)

Answer 6

a loss of H or gain of oxygen (increasing oxygen to hydrogen ratio)

Question 7

oxidation of primary alcohol

Answer 7

aldehyde and carboxylic acid

Question 8

oxidation of secondary alcohol

Answer 8

ketone

Question 9

oxidation of tertiary alcohol

Answer 9

no products formed

Question 10

aldehyde functional group and location

Answer 10

carbonyl C=O at start-end

Question 11

general formula of aldehydes

Answer 11

CnH2nO

Question 12

name of aldeydes

Answer 12

1. ends in ‘al’

2. does not contain a number to show where the functional group is because C=O is always at start

Question 13

ketone functional group and location

Answer 13

carbonyl C=O located in the middle

Question 14

general formula of ketones

Answer 14

CnH2nO n=3 or more

Question 15

name of ketones

Answer 15

1. ends in ‘one’

2. position of C=O functional group must be included in the name

Question 16

oxidation of ethanol experiment

Answer 16

• to facilitate oxidation reaction, an oxidising agent is used
• superwool soaked in ethanol
• copper oxide black –> orange/brown
• damp pH paper turns red (ethanoic acid)

Question 17

reduction of alcohols

Answer 17

gain of H/loss of O

other way round from oxidation eg carboxylic acid –> aldehyde

Question 18

how to distinguish between aldehydes

and ketones

Answer 18

aldehydes can be oxidised to carboxylic acids but ketones cannot be oxidised further
therefore you can tell them apart by oxidation

Question 19

3 oxidising agents (tests) used to distinguish between aldehydes and ketones are:

Answer 19

1. acidified potassium dichromate solution
2. Fehling’s solution (aka Benedict’s solution)
3. Tollen’s Reagent

Question 20

Tollen’s Reagent

Answer 20

colourless –> formation of a silver mirror

tollen’s made from silver ions which are reduced Ag+ (aq) +e- –> Ag (s)

Question 21

Fehling’s solution

Answer 21

blue –> brick red precipitate

Fehling’s made from copper oxide CuO Cu2+(aq) + 2e- –> Cu(s)

Question 22

Acidified potassium dichromate

Answer 22

orange –> green
Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O
acidic conditions to provide H+ ions

Question 23

why would you not want something to oxidise?

Answer 23

if flavour/aroma molecules (aldehydes) are oxidised further they can change the taste and smell of the products
eg oxygen reacts with edible oils giving food a rancid flavour

Question 24

what are antioxidants?

Answer 24

molecules which will prevent oxidation reactions taking place
they are easily oxidised in place of the compounds they have been added to
can be identified as the substance being oxidised in a redox reaction

Question 25

common example of an antioxidant

Answer 25

asorbic acid (vitamin c)

Question 26

diols

Answer 26

alcohols containing two hydroxyl groups

Question 27

triols

Answer 27

alcohols containing three hydroxyl groups

Question 28

why does boiling point increase as the number of hydroxyl groups in an alcohol increase?

Answer 28

hydroxyl groups are polar and this leads to more hydrogen bonding hence more energy is needed to break them.