3.05 Alcohols

• What is the functional group of an alcohol?

  Hydroxyl group -OH
• What is the general formula of an alcohol?

  CnH2n+1(OH)
• How do you name alcohols?

  Hydroxyl- or -ol
• What kind of intermolecular forces do alcohols have?

  Hydrogen bonding due to the electronegativity difference in the OH bond
• How do alcohols' Tb/Tm compare to other hydrocarbons of similar C chain lengths? Why?

  Higher, because they have hydrogen bonding, therefore stronger than VDW forces
• Are alcohols soluble in water? Why does solubility depend on chain length?

  • Soluble when short chain - OH hydrogen bonds to hydrogen bonds present in water
  • Insoluble when long chain - non-polarity of C-H bond takes precedence
• What makes an alcohol primary?

  C bonded to OH is only bonded to one other C atom
• What makes an alcohol secondary?

  C bonded to OH is bonded to two other C atoms
• What makes an alcohol tertiary?

  C bonded to OH is bonded to 3 other carbons
• How can ethanol be made from crude oil?

  Hydration of ethene via electrophilic addition (phosphoric acid catalyst)
• What are the advantages and disadvantages of the hydration of ethene?

  • Advantages - fast, continuous process, ethanol has high purity
  • Disadvantages - not renewable as from crude oil
• How can ethanol be made from fermentation?

  Plant carbohydrates broken down and fermented by enzymes in yeast → ethanol
• What conditions are needed for fermentation to take place?

  Enzymes in yeast as catalyst, 35 degrees celsius, anaerobic conditionsd
• Write an equation for fermentation.

  C6H12O6 (aq) → 2C2H5OH + 2CO2
• What are the advantages and disadvantages of fermentation?

  • Advantages - renewable as from plants
  • Disadvantages - slow, batch process, enzymes stop working at 15% alcohol so solution is not pure, needs to be fractionally distilled
• In the future, how might most ethene be made? Why is it not made like this at the moment?

  • Dehydrate ethanol made by fermentation → ethene
  • Not economical at the moment
• Define carbon neutral.

  No net addition of CO2 into the atmosphere

  • carbon dioxide released when combusted = carbon dioxide absorbed as a plant
• Explain how using ethanol in petrol engines could be considered to be carbon neutral.

  Carbon dioxide released in fermentation and combustion = carbon dioxide absorbed when growing
• Why would it probably not be entirely carbon neutral to use ethanol in petrol engines?

  Other 'carbon costs' associated with it e.g transport
• What is a commercial fuel that uses ethanol? What else does it contain and why?

  Methylated spirits - methanol (toxic therefore cannot be drunk)
• Which group leaves the parent molecule in the case of alcohols?

  OH and a H to form water
• What physical conditions are needed for the elimination from alcohols to alkenes?

  Excess hot concentrated sulphuric acid
• Draw a mechanism for the dehydration of ethanol.


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• Draw a method for dehydration of ethanol in the lab.


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• What happens if you partially oxidise a primary alcohol?

  An aldehyde forms
• What conditions are needed to partially oxidise a primary alcohol?

  • Dilute sulphuric acid
  • Potassium dichromate VI
  • Distill product as it is produced
  • Gentle heating
• Write an equation for the partial oxidation of ethanol.

  CH3CH2OH (l) + [O] → CH3CHO (g) + H2O (l)
• What happens when you fully oxidise a primary alcohol?

  A carboxylic acid.
• What conditions are needed for the complete oxidation of a primary alcohol?

  • Concentrated sulphuric acid
  • Potassium Dichromate VI
  • Reflux for about 20 mins
  • Strong heating
• Write an equation for the full oxidation of ethanol.

  CH3CH2OH (l) + 2[O] → CH3COOH (g) + H2O (l)
• What happens if you oxidise a secondary alcohol?

  A ketone forms
• Why can't a ketone be oxidised further, and why can't a tertiary alcohol be oxidised?

  C-C bond would have to break
• What conditions are needed for the oxidation of a secondary alcohol?

  • Concentrated sulphuric acid
  • Potassium dichromate VI
  • Reflux for about 20 mins
  • Strong heating
• Write an equation for the oxidation of propan-2-ol.

  CH3CH(OH)CH3 (l) + [O] → CH3COCH3 (g) + H2O
• What is an aldehyde? What is its functional group?

  • Molecule with C=O group at the end of a carbon chain
  • Carbonyl functional group C=O
• How do you name aldehydes?

  Suffix -al e.g ethanal
• What is a ketone? What is its functional group?

  • Molecule with C=O group in the middle of a carbon chain
  • carbonyl functional group C=O
• How do you name ketones? Give an example.

  Suffix -one e.g propanone
• What is a carboxylic acid? What is its functional group?

  • Molecule with COOH froup, which has to be at the end of a carbon chain.
  • Carboxyl functional group, made up of carbonyl C=O and hydroxyl -OH
• How do you name carboxylic acids? Give an example.

  Suffix -oic acid e.g propanoic acid