Alcohols

Question 1

What do all alcohols contain?

Answer 1

O-H bond

Question 2

What are the names and structural formula of the first four alcohols?

Answer 2

• Methanol - CH₃OH
• Ethanol - CH₃CH₂OH
• Propanol - CH₃CH₂CH₂OH
• Butanol - CH₃CH₂CH₂CH₂OH

• The displayed formula of ethanol is shown in the image for reference
• These are the structural formulae, the molecular formula for ethanol, for example, is C₂H₅OH. Note how you still leave OH in as it is the functional group

Question 3

What are the three ways that ethanol can be oxidised?

Answer 3

• Complete combustion
• Microbial oxidation
• Heating with potassium dichromate(VI) in dilute sulfuric acid

Question 4

What is the balanced symbol equation for the complete combustion of ethanol in air?

Answer 4

C₂H₅OH + 3O₂ –> 3H₂O + 2CO₂

Question 5

How is ethanol oxidised through microbial oxidation?

Answer 5

• Bacteria in the air use atmospheric oxygen to oxidise the ethanol and create ethanoic acid and water
• Symbol equation: C₂H₅OH + O₂ –> CH₃COOH + H₂O

This is what happens if you leave wine out for too long. It will taste vinegary due to the ethanoic acid formed

Question 6

How is ethanol oxidised using potassium dichromate (VI)?

Answer 6

• Ethanol is heated with potassium dichromate in dilute sulfuric acid
• The potassium dichromate acts as an oxidising agent which oxidises the ethanol, producing ethanoic acid and water
• Symbol equation: C₂H₅OH + [O] –> CH₃COOH + H₂O

• The [O] just means the oxidising agent, as other things could be used
• Other products will be produced, but they will depend on the oxidising agent used

Question 7

What are the two ways in which ethanol can be manufactured?

Answer 7

• Hydration of ethene
• Fermentation

Question 8

What are the conditions necessary for the reaction which manufactures ethanol through the hydration of ethene?

Answer 8

• 60-70 atm
• 300 degrees celsius
• Presence of solid phosphoric acid (H₃PO₄) catalyst

Question 9

How is ethanol manufactured through the hydration of ethene?

Answer 9

• Ethene is reacted with steam in the presence of a phosphoric acid (H₃PO₄) catalyst under the correct conditions
• Then, the ethanol and remaining ethene and water are seperated through fractional distilliation
• Symbol equation: C₂H₄ + H₂O –> C₂H₅OH

• It is steam because the reaction happens at 300 degrees, but at the seperation stage, the remaining steam is water because the temperature is lower again
• This is less favourable due to how it comes from non-renewable crude oil resources

Question 10

How is ethanol manufactured through fermentation?

Answer 10

• Yeast is added with glucose to water, and left for a few days in the absence of oxygen and at 30 degrees celcius
• The yeast respire anaerobically using the glucose to produce ethanol and carbon dioxide
• It must be without oxygen for anaerobic respiration to occur, and 30 degrees celcius is the optimal temperature for the enzymes in yeast which break down the sugar to function
• Symbol equation: C₆H₁₂O₆ (+ yeast enzymes) –> 2CO₂ + C₂H₅OH

• It is literally just the equation for anaerobic respiration in plants
• This is good as it is from renewable resources