2.7 alcohols and carboxylic acids

Question 1

what is the functional group of alcohol’s?

Answer 1

R-OH (hydroxyl)

Question 2

what is the general formula for alcohols?

Answer 2

CnH2n+1OH

Question 3

what are the conditions for the industrial preparation of ethanol from ethene?

Answer 3

hydration of ethene:
phosphoric acid catalyst (aq)
temperature of 300°c
pressure of 60-70atm

Question 4

write the chemical equation for the hydration of ethene

Answer 4

CH2=CH2 + H2O –> CH3CH2OH

Question 5

how can ethanol be produced from a renewable source?

Answer 5

ethanol can be produced from the fermentation of sugars. in crops (yeast) enzymes break down starch into sugars which can then undergo fermentation to form ethanol

Question 6

what conditions are required for the fermentation of glucose to form ethanol?

Answer 6

• carried out with yeast as a catalyst
• 30-40° temp
• anaerobic conditions (no oxygen)

Question 7

what is chemical equation for the fermentation of glucose to form ethanol?

Answer 7

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Question 8

after fermentation how can ethanol be separated from the rest of the reaction mixture?

Answer 8

fractional distillation

Question 9

why is the production of ethanol fuel from the glucose said to be carbon neutral?

Answer 9

ethanol fuel, produced from glucose, is carbon neutral because the crops take in carbon dioxide during photosynthesis which balance out the amount of carbon dioxide that is released when the fuel is burned

Question 10

why might someone argue that the production of ethanol is not carbon neutral?

Answer 10

• energy required to power the machinery to make fertilisers for the crops and to harvest the crops, which releases carbon dioxide
• carbon dioxide released during transport
• land use for fuel rather than food

Question 11

what is formed when alcohols undergo dehydration?

Answer 11

alkenes

Question 12

how do alcohols undergo dehydration reactions?

Answer 12

form alkene and water molecule
two ways of dehydration:
- heat with concentrated sulphuric acid
- pass alcohol vapour over aluminium oxide powder

Question 13

what is the chemical equation for the dehydration of propane-2-ol to form prop-2-ene?

Answer 13

CH3CH(OH)CH₃ → CH₂CHCH₃ + H₂O

Question 14

How are primary alcohols oxidised to aldehydes?

Answer 14

heat with acidified potassium dichromate, to oxidise alcohol to aldehyde
-distill
CH₃OH + [O] → CH₂=O (aldehyde) + [O] → CH=OOH
acidified potassium dichromate will change colour from orange to green

Question 14

explain the classification of alcohols

Answer 14

• primary 1° - the OH group is bonded to one carbon that itself is only bonded to 1 other
  secondary 2° - OH group is joined to a carbon that itself is bonded to two others
  tertiary 3° - OH group is bonded to a carbon that itself is bonded to 3 others

Question 15

how are primary alcohols oxidised to carboxylic acids?

Answer 15

• heat with acidified potassium dichromate
  -reflux
  colour change from orange to green
  CH₃OH + 2[O] → CH=OOH + H2O

Question 16

how are secondary alcohols oxidised to ketones?

Answer 16

• heat under reflux with acidified potassium dichromate to form ketone
  colour change from orange to green
  CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H20

Question 17

will there be oxidation of tertiary alcohols? - no reaction so no

Answer 17

no reaction so no

Question 18

what qualitative test can be carried out to test for carboxylic acids?

Answer 18

• add sodium hydrogencarbnate (NaHCO₃)

the solution will effervesce and carbon dioxide will be produced if carboxylic acid is present. the gas released can be tested with limewater to identify it as carbon dioxide

Question 19

what is produced when carboxylic acids react with bases?

Answer 19

salt and water

Question 20

what is the chemical equation for the reaction of ethanoic acid with sodium hydroxide?

Answer 20

CH₃COOH + NaOH → CH₃COONa + H₂0

Question 21

what is produced when carboxylic acids react with carbonates?

Answer 21

salt, carbon dioxide and water

Question 22

what is the chemical equation for the reaction of methanol acid with sodium carbonate?

Answer 22

2HCOOH + Na₂CO₃ → 2HCOONa + CO₂ + H₂O

Question 22

what is the equation for methanoic acid and copper oxide?

Answer 22

2HCOOH + CuO → (HCOO)₂Cu + H₂O

Question 23

what is produced when carboxylic acids react with solid base copper oxide

Answer 23

a solid salt and water

Question 24

how do alcohols react with carboxylic acids?

Answer 24

• alcohol’s react with carboxylic acids to form esters
• esterification which requires heating with a sulfuric acid catalyst

Question 25

how to test for alcohols or carboxylic acids with esters?

Answer 25

characteristic sweet fruity odour occurs

Question 26

explain how ethanol can be separated from water

Answer 26

• ethanol and water have different boiling points so they can be separated by distillation
• mixture is heated until ethanol evaporates
• ethanol vapours enters the condenser where they condense and run into beaker

Question 27

ester of carboxylic acid with water -

Answer 27

esters have the lowest boiling temperature and do not hydrogen bond

Question 28

fermentation or hydration better? why?

Answer 28

• hydration = 100% atom economy
• fermentation uses glucose which is renewable rather than crude oil
• fermentation only warm countries can grow sugar crops
• fermentation uses lower temperatures and pressures so less explosive
  hydration - does not use unnecessary land