Module 4.2 - Alcohols, Haloalkanes and Analysis Flashcards
What is the general formula of alcohols?
CnH2n+1OH
What are the 3 groups an alcohol can be classified as?
- primary alcohol
- secondary alcohol
- tertiary alcohol
What is a primary alcohol?
Has the functional group attached to a carbon with no more than one alkyl group
What is a seconday alcohol?
Has the functional group attached to a carbon atom with two alkyl groups
What is a tertiary alcohol?
Has the functional group attached to a carbon atom with three alkyl groups
Explain the trend in boiling point of alcohols as chain length increases.
- bp increases as chain length increases
- more areas of surface contact as higher Mr
- stronger induced dipole dipole intermolecular forces
- more energy to overcome these attractive forces so higher bp
How does the boiling point of alcohols compare to their corresponding alkanes?
- bp of alcohols higher than corresponding alkanes
- H bonds between alcohol molecules
- H bonds stronger than London forxes
- so more energy needed to overcome
- so higher bp
Describe the volatility of alcohols. How does this compare to the corresponding alkane?
- volatile substances evaporate at RTP
- volatility increases as bp decreases
- increases in chain length = decrease in volatility
- less volatile than corresponding alkane from H bonds
Describe the solubility of alcohols in water, and how this is affected by an increase in chain length.
- water molecules are polar as is the alcohol functional group
- methanol, ethanol and propanol are soluble in water as form H bonds w water (sometimes described as miscibility)
- as chain length increases, solubility of alcohol decreases as the aliphatic chain can’t form H bond and this becomes the larger part of the molecule
What are the products when an alcohol burns completely?
- carbon dioxide
- water
Describe the distillation of primary alcohols.
- gently heat
- forms an aldehyde (partial oxidation)
- acidified potassium dichromate (VI) (K2Cr2O7, Cr2O72-) and sulphuric acid (H2SO4, H+) catalysts
C2H5OH + [O] –> C2H3HO + H2O
- aldehyde formed has to be distilled immediately to prevent further reaction
- colour change from orange to green
Describe the reflux of primary alcohols.
- heat strongly
- forms an carboxylic acid (full oxidation)
- acidified potassium dichromate (VI) (K2Cr2O7, Cr2O72-) and sulphuric acid (H2SO4, H+) catalysts
C2H5OH + 2[O] –> C2H3HO + H2O
-colour change from orange to green
Describe the reflux of secondary alcohols.
- heat strongly
- forms an ketone (full oxidation)
- acidified potassium dichromate (VI) (K2Cr2O7, Cr2O72-) and sulphuric acid (H2SO4, H+) catalysts
C2H5OH + [O] –> C2H3HO + H2O
-colour change from orange to green
What is reflux?
The constant boiling and condensing of a reaction mixture. This ensures that the reactions goes to completion as fully as possible without losing reactants or products as vapour goes into the air
How could you use a laboratory test to classify an unknown alcohol?
- heat the test alcohols w excess acidified potassium dichromate (VI) under reflux
- if no colour change to green it’s tertiary
- if colour change to green, distil product and test w Fehling’s solution or Tollen’s reagent
- second colour changes indicates test alcohol is secondary, but no second colour change indicates test alcohol is primary
Describe the dehydration of an alcohol.
- water is lost from organic compound
- elimination reaction
- alcohols heated w strong acid (e.g. H2SO4) water elimintated to make an alkene
- OH group from one C and H from adjacent C lost to form water
- π bond forms between the 2 adjacent C atoms