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Chemistry module 4 > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

What is the functional group of alcohols

A
  • OH
  • hydroxyl group
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2
Q

What is the OH group responsible for doing

A
  • responsible for both physical and chemical properties of alcohols
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3
Q

What can methanol be used for

A
  • high performance fuel - efficient combustion
  • important chemical feedstock - tarting material for many industrial synthesis
  • polymers
  • paints
  • solvents
  • insulatio
  • adhesives
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4
Q

What is ethanol used for

A
  • alcoholic drinks
  • fuel
  • solvent
  • feedstock
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5
Q

how do you compare alcohols and alkanes

A

by using the alcohol and alkane with the same number of carbon atoms

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6
Q

Describe the difference in polarity and boiling points between alcohols and alkanes

A
  • 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
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7
Q

What is the difference between alkanes and alcohols with volatility and boiling points

A
  • 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
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8
Q

Compare the solubility of alcohols and alkanes in water

A
  • 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
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9
Q

What is the relationship of increasing chain length and solubility

A
  • as hydrocarbon chain increases influcence of OH group becomes relativley smaller and solubility decreases
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10
Q

What are primary alcohols and give examples

A
  • like methanol and ethanol
  • Oh group is attatched o a carbon atom attatched to two hydrogen atoms and one alkyl group
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11
Q

How come methanol is a primary alcohol

A
  • three hydrogen atom and no other carbons attatched
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12
Q

What is a secondary alcohol and give examples

A
  • 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
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13
Q

What is a tertiary alcohol and give examples

A
  • 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
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14
Q

Describe the combustion of alcohols

A
  • 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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15
Q

Describe what happens to the amount of heat produced with chain increasing

A
  • quantity of heat released per mole increases
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16
Q

Write the equation for the complete combustion of ethanol

A

C2H5OH(l) +3O2(g) -> 2CO2 (g) + 3H2O (l)

17
Q

Describe the oxidation of alcohols

A
  • 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
18
Q

Describe the oxidation of primary alcohols

A
  • can be oxidised to either aldehydes or carboxylic acids
  • depends on the reaction conditions
19
Q

Describe the preparation of aldehydes from alcohols

A
  • 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
20
Q

Describe the preparation of carboxylic acids from alcohols

A
  • 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
21
Q

Briefly desccribe the conditions of oxidation of primary alchols

A
  • when preparing adehyde use distillation to remove the aldehyde from the reaction mixture
  • when preparing the carboxylic acid heat alcohol under reflux
22
Q

Describe the oxidation of secondary alcohols

A
  • 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
23
Q

Describe the oxidation of tertiary alcohols

A
  • tertiary alcohols do not undergo oxidation reactions
  • acidified dichromate (VI) remains orange when added to a tertiary alcohol
24
Q

Describe the dehydration of alcohols

A
  • 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
    *
25
Q

Describe the substitution of alcohols

A
  • 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

Chemistry module 4 (7 decks)

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