Alcohols

• What is the general formula of alcohols?

  CnH2n+1OH
• How do you name alcohols ?

  Hydroxy- if there is another higher ranked functional group OR -ol
• How do you get from a primary alcohol to an aldehyde

  Oxidation with potassium dichromate (VI) solution and dilute sulfuric acid.

  
  

  Conditions: (use a limited amount of dichromate) warm gently and distil.
• What is observed when partially oxidising a primary alcohol.

  Orange to green colour change.
• Why are electric heaters used when distilling alcohols?

  They are highly flammable so could set on fire with an open flame.
• How do you get from a primary alcohol to a carb acid?

  Oxidation with potassium dichromate(VI) solution and dilute

  sulfuric acid

  
  

  Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)
• What is observed when oxidising a primary alcohol under reflux?

  Orange to green colour change.
• How do you get from a secondary alcohol to a ketone?

  Oxidise with potassium dichromate(VI) solution and

  dilute sulfuric acid.

  
  

  Conditions: heat under reflux
• What is observed when oxidising secondary alcohols?

  Orange to green colour change.
• Can tertiary alcohols be oxidised, why?

  Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the -OH group
• What two reagents can be used to distinguish between aldehydes and ketones?

  Tollens and fehlings
• What is tollens reagent made from

  It is formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+ .
• How do you use tollens to distinguish between aldehydes and ketones.

  Heat the reagent with both separately.

  
  

  aldehydes are oxidised by Tollens reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms which forms a silver mirror inside the test tube

  
  

  Ketones result in no visible change as they cannot be further oxidised.
• What is fehlings solution made from?

  Contains blue Cu 2+

  ions.
• How do you use fehlings to distinguish between aldehydes and ketones?

  Heat gently with both separately.

  
  

  aldehydes are oxidised by Fehling's solution into a carboxylic acid. The copper (II) ions are reduced to copper(I) oxide . This results in the blue Cu 2+ ions in solution change to a red precipitate of Cu2O.

  
  

  Ketones do not react
• How do you test for a carboxylic acid?

  Add Na2CO3 which will produce CO2. Then add limewater and a cloudy solution should be present.
• How do you get from an alcohol to an Alkene?

  Dehydration/elimination

  
  

  Reagents: Concentrated sulfuric or phosphoric acids

  
  

  Conditions: warm (under reflux)
• What are the two methods of forming ethanol?

  Fermentation and industrial formation form ethene.
• Describe fermentation process of making ethanol.

  Glucose = ethanol + carbon dioxide

  
  

  Conditions: yeast, anaerobic conditions, 30-40 degrees. (Optimum 38)
• Why is 38 degrees optimum for fermentation?

  At lower temperatures the reaction is too slow.

  
  

  At higher temperatures the yeast dies and the enzymes denature.

  
  

  Fermentation is done in an absence of air because the presence of air can cause extra reactions to occur.

  
  

  It oxidises the ethanol produced to ethanoic acid (vinegar).
• What are the advantages of fermentation?

  sugar is a renewable resource

  
  

  production uses low level technology / cheap equipment
• What are the weaknesses of fermentation?

  batch process which is slow and gives high production costs

  
  

  ethanol made is not pure and needs purifying by fractional distillation

  
  

  depletes land used for growing food crops
• What is the process of the industrial production of ethene.

  Ethene is hydrated with a molecule of water and the conditions: high temp (300 degrees) 70 atms and a strong acid catalyst (conc H4PO4)
• What are the advantages hydration of ethene?

  fast process, produces pure ethanol, continuous process, low labour costs.
• What are the weaknesses of hydration of ethene?

  high technology equipment needed (expensive initial costs)

  
  

  ethene is non-renewable resource (will become more expensive when raw materials run out)

  
  

  high energy costs for pumping to produce high pressures
• What is biofuel?

  A fuel produced from plants
• Is ethanol produced via fermentation a biofuel?

  Yes
• Is ethanol produced via fermentation carbon neutral?

  It can be argued that ethanol produced from this method is classed as carbon-neutral because plants take in 6 mols of CO2 to make one mol of glucose via photosynthesis. This is produced in the fermentation process to produce one one mol of ethanol and two mols of CO2. Combusting the ethanol produces 4 mols of CO2.

  
  

  This means that the chemical process of creating and using ethanol is carbon neutral. However the biofuel requires transport and machinery that requires fossil fuels to be burnt releasing CO2.
• Why did we change from fermentation to industrial production of ethanol

  Direct hydration route produces pure ethanol
• Describe a test-tube reaction, on the product, to show that the cyclohexanol had been dehydrated.

  bromine water it would from orange to colourless
• Explain why cyclohexene has a shorter retention time than cyclohexanol.

  cyclohexanol is more polar than cyclohexene so cyclohexanol has a greater affinity/attraction for the stationary phase/silica