Alcohols

Question 1

What is the general formula for alcohols?

Answer 1

CnH(2n+1)OH

Question 2

What are the required conditions for fermentation?

Answer 2

• Sugars in aqueous solution
• Yeast
• 30-40 degrees C, a lower temperature will deactivate enzymes and a higher temperature will denature them
• Anaerobic conditions

Question 3

What is the formula for fermentation?

Answer 3

C6H12O6 –> 2C2H5OH + 2CO2

Question 4

What are the benefits of fermentation?

Answer 4

• It is carbon neutral

- Cheap equipment

Question 5

What are the drawbacks of fermentation?

Answer 5

• Batch process
• Slow
• Higher temperatures cannot be used to increase the rate of reaction
• Low yield
• Ethanol is impure and fractional distillation is required if we want a more concentrated solution

Question 6

What are the conditions required for the hydration of ethene?

Answer 6

• Steam
• Phosphoric acid catalyst
• 300 degrees C
• 6.5 x 10^3 kPa

Question 7

What is the equation for the hydration of ethene?

Answer 7

C2H4 + H2O –> C2H5OH (g)

Reversible

Question 8

What are the benefits of hydration of ethene?

Answer 8

• Unconverted ethene can be separated from ethanol and steam when gases cool, so it can be recycled
• Relatively concentrated ethanol is formed
• Continuous process
• Fast reaction
• Cheap on manpower

Question 9

What are the drawbacks of hydration of ethene?

Answer 9

• Ethene is non-renewable

- Expensive equipment

Question 10

What are the uses of ethanol?

Answer 10

• Solvent
• Cosmetics
• Thinners
• Biofuels
• Printing ink

Question 11

How does the oxidation of primary alcohols work?

Answer 11

• Na2Cr2O7 (sodium dichromate) as the oxidising agent
• Warmed
• Aldehydes are formed, with a lower boiling point tan alcohols they immediately distil off, preventing further oxidation to carboxylic acids
• CH3CH2OH + [O] –> CH3CHO + H2O

Question 12

How does further oxidation of primary alcohols work?

Answer 12

• Na2Cr2O7 as the oxidising agent
• H2SO4 concentrated catalyst
• Heat under reflux
• Reflux is a process in which a reaction mixture is heated in a flask with a condenser to prevent loss of volatile substances including the solvent
• CH3CH2OH + 2[O] –> CH3COOH + H2O

Question 13

How does oxidation of secondary alcohols work?

Answer 13

• Na2Cr2O7 as the oxidising agent
• Dilute H2SO4 catalyst
• Gentle reflux
• Product removed by distillation
• Ketones are resistant to oxidation
• They contain a carbonyl group (C=O) that can be attached to any carbon except those at the end or else it would be an aldehyde
• CH3CH(OH)CH3 + [O] –> CH3COCH3 + H2O

Question 14

How does oxidation of tertiary alcohols work?

Answer 14

• They are not easily oxidised

- No H bonded to the carbon attached to the -OH group

Question 15

How can Fehling’s solution be used to test for aldehydes and ketones?

Answer 15

• Fehling’s solution is blue
• Aldehyde = brick red precipitate
• Ketone = no colour change

Question 16

How can Tollen’s reagent be used to test for aldehydes and ketones?

Answer 16

• Tollen’s reagent is Colourless
• Aldehyde = silver mirror
• Ketone = no change

Question 17

How can you test for a tertiary alcohol?

Answer 17

• Tertiary alcohols are very resistant to oxidation
• If oxidation occurs, the orange solution of sodium dichromate is reduced to a green solution containing Cu3+ ions
• There will be no colour change if the alcohol is tertiary

Question 18

How does elimination of alcohols work?

Answer 18

• Alcohols can be dehydrated by hot, concentrated acids to form alkenes
• One molecule of water is eliminated
• H2PO4 or H2SO4 catalyst
• CH3CH2OH –> C2H4 + H2O

Question 19

How can alkenes be used?

Answer 19

• In addition polymerisation reactions

- Alternative method to produce alkenes as opposed to cracking