Alcohols Flashcards
What is the functional group of alcohols
- OH
- hydroxyl group
What is the OH group responsible for doing
- responsible for both physical and chemical properties of alcohols
What can methanol be used for
- high performance fuel - efficient combustion
- important chemical feedstock - tarting material for many industrial synthesis
- polymers
- paints
- solvents
- insulatio
- adhesives
What is ethanol used for
- alcoholic drinks
- fuel
- solvent
- feedstock
how do you compare alcohols and alkanes
by using the alcohol and alkane with the same number of carbon atoms
Describe the difference in polarity and boiling points between alcohols and alkanes
- alkanes have non polar bonds because the electronegativity between hydrogen and carbon are very similar
- alkane molecules are therfore non polar
- intermoleclar forces between non polar molecule are very weak london forces
- alcohols have a polar O-H bond because of the differences in negativity of the oxygen and hydrogen atoms
- alcohols are therefore polar
- weak london forces but also much stronger hydrogen bonds between polar OH groups
What is the difference between alkanes and alcohols with volatility and boiling points
- alchols have a higher boiling and melting point than alkanes
- in liquid state hydrogen bonds hold alcohol molecules together
- these bonds must be broken in order to change liquid alcohol into a ga
- require more enrgy than overcoming only weak london forces in alkanes
- alcohols have a lower volatility than alkanes with the same number of carbon atoms
Compare the solubility of alcohols and alkanes in water
- alkanes are non polar so they cannot form hydrogen bonds with water
- alcohols are completley soluble in water as hydrogen bonds form between polar OH groups of alcohol and water molecules
What is the relationship of increasing chain length and solubility
- as hydrocarbon chain increases influcence of OH group becomes relativley smaller and solubility decreases
What are primary alcohols and give examples
- like methanol and ethanol
- Oh group is attatched o a carbon atom attatched to two hydrogen atoms and one alkyl group
How come methanol is a primary alcohol
- three hydrogen atom and no other carbons attatched
What is a secondary alcohol and give examples
- Oh group is attatched to a carbon atom that is atttched to on ehydrogen atom and two alkyl groups
- propan-2-ol and propan -3ol are examples
What is a tertiary alcohol and give examples
- Oh groups is attatched to a carbon atom attatched to no hydrogen atoms and three alkyl groups
- 2-methylpropan-2-ol and 2 methylbutan-2-ol
Describe the combustion of alcohols
- alcohols burn completley in a plentiful supply of oxygnen to produce carbon dioxide and water
- reaction is exothermic releasing a large quantity of energy in the form of heat
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Describe what happens to the amount of heat produced with chain increasing
- quantity of heat released per mole increases
Write the equation for the complete combustion of ethanol
C2H5OH(l) +3O2(g) -> 2CO2 (g) + 3H2O (l)
Describe the oxidation of alcohols
- primary and secondary alcohols can be oxidised via an oxidising agent
- potassium dichromate (VI) K2Cr2O7 acidified with dilute sulfuric acid H2SO4
- if alcohol is oxidised the orange containin gthe dichromate ions (VI) ions is reduced to a green solution containing chrominum (III) ions
Describe the oxidation of primary alcohols
- can be oxidised to either aldehydes or carboxylic acids
- depends on the reaction conditions
Describe the preparation of aldehydes from alcohols
- gentle heating of primary alcohols with acidified potasium dichromate an aldehyde is formed
- ensure aldehyde is prepared rather than carboxylic aci the aldehyde is distilled out of the reaction mixture as it forms
- prevents any further reaction with oxidising agent
- dichromate (VI) ions changes colour from orange to green
Describe the preparation of carboxylic acids from alcohols
- primary alcohol heated strongly under reflux with excess of acidifies potasium dichromate (VI) a carboxylic acid is formed
- excess of acidified potassium dichromate (VI) ensures that all of the alcohol is oxidised
- heating under reflux ensures than any adlehyde is formed initially undergoes oxidation to the carboxylic acid
Briefly desccribe the conditions of oxidation of primary alchols
- when preparing adehyde use distillation to remove the aldehyde from the reaction mixture
- when preparing the carboxylic acid heat alcohol under reflux
Describe the oxidation of secondary alcohols
- oxidised to ketons
- not possible to further oxidise kketons using acidified dichromate (VI) ions
- ensure reaction goes o completion secondary alcohol is heated under reflux with the oxidising miture
- dichromate (VI) ions once again changes colour from orange to green
Describe the oxidation of tertiary alcohols
- tertiary alcohols do not undergo oxidation reactions
- acidified dichromate (VI) remains orange when added to a tertiary alcohol
Describe the dehydration of alcohols
- water molecule is removed from alcohol
- is is heated under reflux in the precence of an acid catalyst such as concentrated sulfuric acid H2SO4 of concentrated phosphoric acid H3PO4
- product is an alkene
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Describe the substitution of alcohols
- alchols react with hydrogen halides to form haloalkanes
- when preparing a haloalkane the alcohol is heated under reflux with sulfuric acid and a sodium halid the hydrogen bromide is formed in situ
- HBR then reats ith alcohol to produce haloalkane
