3.5 Alcohols

• what functional group do alcohols have?

  -OH (hydroxyl)
• what is a primary alcohol?

  when there is one group attached to the carbon with the hydroxyl group
• what is a secondary alcohol?

  when there are two groups attached to the carbon with the hydroxyl group attached
• what is a tertiary alcohol?

  when there are three groups attached to the carbon with an alcohol group attached
• how can alkenes be made from alcohols sustainably?

  providing alcohol has been made via fermentation of glucose from plants, we can eliminate water from an alcohol to produce an alkene during dehydration
• What are the conditions for dehydration?

  acid catalyst either conc H2SO4 or conc H3PO4
• why use fermentation of plants?

  more sustainable compared to the normal way of producing alkenes which is sourced from crude oil
• how is dehydration of alcohols conducted?

  via distillation to separate the useful alkene from impurities due to the difference in boiling points
• how can you purify the product further?

  using a separating funnel and adding a drying agent afterwards
• how are alcohols produced from alkenes? what are the reagent and conditions?

  by hydration of alkenes with steam and phosphoric acid catalyst at 600*C and 60atm
• what are the conditions needed for fermentation of yeast?

  anaerobic conditions due to presence of yeast enzyme at 30-40*C
• what are biofuel?

  fuels made from dead biological matter
• what are the advantages of biofuel?

  - biofuels are renewable so they are more sustainable than crude oil

  - biofuels produce CO2 when they are burnt however they are classes as carbon neutral as the CO2 is absorbed by the sugar can when its growing
• what are the disadvantages of biofuel?

  - expensive to convert existing petrol engines to take fuels with a higher concentration of ethanol

  - land that could have been used to grow food is being used to make fuel. this could cause food shortages in countries that grow sugar cane
• why is biofuel considered carbon neutral?

  the total number of moles of CO2 produces is the same as the number of moles used up
• give equations to show how biofuels are nearly carbon neutral?

  Photosynthesis:

  6CO2 + 6H2O -> C6H12O6 + 6O2

  Fermentation:

  C6H12O6 -> 2CO2 + 2C2H5OH

  Combustion:

  2C2H5OH + 6O2 -> 4CO2 + 6H2O
• why is biofuel not considered 100% carbon neutral?

  - fossil fuels are burnt to transport the biofuel across the country

  - fossil fuels are used to make fertilisers put on the crops and on the machinery to harvest the crop
• what can alcohols be oxidised to using what?

  aldehydes, ketones and carboxylic acids using acidified potassium dichromate as the chromium is reduced from Cr2O72- to Cr3+
• what is observed if an alcohol is oxidised?

  turn from orange to green
• what are primary alcohols oxidised to?

  aldehydes under distillation and then carboxylic acids under reflux
• what are secondary alcohols oxidised to?

  ketones under reflux
• how are tertiary alcohols oxidised?

  only by burning as can't be oxidised by dichromate
• what does reflux allow?

  reflux allows strong heating without losing volatile reactants and products
• how can you distinguish between aldehydes and ketones?

  Fehling's solution:

  - Aldehydes - blue to brick red precipitate

  - ketones - no visible change

  Tollens' reagent:

  - Aldehydes - silver mirror

  - ketones - no visible change