4.2.1 Alcohols

Question 1

what functional group do alcohols contain

Answer 1

• hydroxyl OH

Question 2

what is the general formula of an alcohol

Answer 2

• CnH2n+1 OH

Question 3

what are some general differences in physical properties between alcohols and alkanes with the same number of carbon atoms

Answer 3

• alcohols are less volatile, higher mp/bp and greater water solubility

Question 4

what is the reason for differences in physical properties between alcohols + alkanes with same no of C

Answer 4

• alkanes have non-polar bonds as electronegativity of H and C very similiar
  > alkane = non polar so very weak London forces
• alcohol has polar O-H bond because of electronegativity difference
  > alcohol = polar so have weak LF + stronger hydrogen bonds between polar O-H

Question 5

why do alcohols have high mp + are less volatile

Answer 5

• hydrogen bonds between OH require lots of energy to overcome

Question 6

are alcohols soluble in water + why

Answer 6

• soluble in water
  > hydrogen bonds form between the polar OH group of alcohol and water molecules

Question 7

what happens to solubility as the hydrocarbon chain in alcohol increases

Answer 7

• solubility decreases
  > influence of the OH polarity decreases and solubility of longer chains decreasw

Question 8

why are alcohols very good solvents

Answer 8

• can dissolve both polar and non-polar molecules

Question 9

what are the 3 different ways alcohols can be classified as

Answer 9

• primary
• secondary
• tertiary

Question 10

alcohols can undergo combustion to produce what

Answer 10

• CO2 + H2O
  > releases heat

Question 11

which types of alcohols can be oxidised

Answer 11

• primary + secondary

Question 12

what can alcohols be oxidised by

Answer 12

• an oxidising agent

Question 13

what can primary alcohols be oxidised to

Answer 13

• aldehyde
• carboxylic acid

Question 14

how can you make an aldehyde from an alcohol

Answer 14

• oxidation of primary alcohol
• heat + distill with acidified potassium dichromate (oxidising agent)
  > aldehyde formed

Question 15

what happens to dichromate ions in oxidation of alcohols

Answer 15

• reduced from orange to green

Question 16

how do you prevent oxidation of aldehyde into carboxylic acid

Answer 16

• aldehyde removed by distillation as its formed
  > aldehyde has has lower boiling point than alcohol

Question 17

why do aldehydes have lower bp than alcohols

Answer 17

• because they don’t have hydrogen bonds

Question 18

how can you form a carboxylic acid from an alcohol

Answer 18

• primary alcohol heated strongly under reflux with excess of acidified potassium dichromate

Question 19

why do you need excess oxidising agent for formation of carboxylic acid

Answer 19

• to ensure that all of the alcohol is oxidised

Question 20

what does a secondary alcohol oxidise to form

Answer 20

• ketones

Question 21

how can you form a ketone from an alcohol

Answer 21

• secondary alcohol oxidised under reflux with acidified potassium dichromate

Question 22

what can tertiary alcohols oxidise to from

Answer 22

• nothing
• tertiary alcohols do not undergo oxidation reactions

Question 23

what is dehydration

Answer 23

• a reaction in which a water molecule is removed from a starting material

Question 24

how do alcohols undergo dehydration + what forms

Answer 24

• alcohol heated under reflux with acid catalyst e.g. conc sulfuric acid or phosphoric acid
• product is an alkene

Question 25

what is the dehydration of an alcohol an example of

Answer 25

- elimination reaction

Question 26

how are haloalkanes formed from alcohols

Answer 26

- alcohols react with hydrogen halides - alcohol heated under reflux with sulfuric acid + sodium halide (which forms a hydrogen halide) - hydrogen halide reacts with alcohol to form a haloalkanes + water

Question 27

what type of reaction is it when an alcohol turns into a haloalkane

Answer 27

- substitution