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A Level Chemistry: Organic Chemistry > Chapter 15: Alcohols > Flashcards

Chapter 15: Alcohols Flashcards

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1
Q

What is the general formula and functional group of Alcohols

A
  • CnH2n+1OH
  • Have a hydroxyl group (-OH) attached to the hydrocarbon chain
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2
Q

How do you name alcohols

A
  • Find longest chain -OH is attached to
  • Place the -OH on the lowest possible number for the chain
  • Remove -e from alkane and add -ol
  • Use numbers to show position isomers
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3
Q

What do you do if there is more than 1 hydroxyl group (more than 1 -OH)

A
  • Use names to say how many (di, tri, tetra)
  • e.g propane 1, 2, 3 - triol
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4
Q

In alcohols what are the shapes and bonding angles

A
  • The oxygen atom has 2 bonding pairs and 2 lone pairs
  • The C-O-H bond angle is 105 (104.5). Angle of tetrahedron is squeezed down in presence of lone pairs
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5
Q

What are the different classification of alcohols and give examples

A
  • Primary alcohol (1º) - has -OH group at the end and attached to carbon that is attached to 1 other carbon (e.g Propan-1-ol)
  • Secondary alcohol (2º) - has -OH group in the body of the chain and -OH attached to carbon that is attached to 2 other carbons (e.g propan-2-ol)
  • Tertiary alcohol (3º) - has -OH group attached to a C bonded to 3 other C. (e.g methyl propan-2-ol)
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6
Q

What are the Physical Properties of alcohols

A
  • High melting and boliling points (-OH group means hydrogen bonding occurs between molecules)
  • Water soluble
    • The -OH group can hydrogen bond to water molecules but non-polar hydrocarbon can’t
    • Longer chain (non-polar hydrocarbon chain dominates) - insoluble
    • Shorter chain soluble in water (hydrogen bond pre-dominates)
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7
Q

What is a substances boiling point a measure of

A
  • A substances boiling point is a measure of the intermolecular forces present between particles
  • Noble gases show a gradual increase in boiling points, hydrides (element joined to H) also show trend
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8
Q

What is the formula of ethanol and what are the 2 ways it can be produced

A
  • C2H5OH
  • By product of anaerobic respiration (fermentation of alcohols)
  • Manufacture industrially with ethene (hydration of ethene)
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9
Q

Why are alcohols and ethanol important

A
  • Alcohols are used as intermediates and easily made and converted into other compounds
  • Ethanol used as intermediate in the manufacture of other organic compounds and used in cosmetics, perfumes
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10
Q

What is fermentation of alcohols

(conditions, raw materials, raw material type, type of process, reaction rate, purity of ethanol)

A
  • Fermentation is a process where glucose is converted to alcohol as a byproduct of anarobic respiration in yeast (C6H12O6→2C2H5OH + 2CO2)
  • Conditions: 35ºc, normal atmospheric pressure, catalyst: enzyme in yeast zymase, aqueous and anaerobic
  • Raw material (type): Carbohydrate crop (renewable)
  • Type of process: batch (stop/start)
  • Reaction rate (slow)
  • Purity of ethanol - impure (needs fractional distillation) Once fermenting solution has 15% ethanol (enzymes dont work) removed by FD (78ºC BP 100º H20)
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11
Q

What happens if there is oxygen in fermentation

A
  • Oxygen can oxidise ethanol to ethanoic acid
  • C2H5OH + 2[O] →CH3COOH + H2O
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12
Q

Apart from fermentation, what is the other way to produce ethanol

A
  • Making ethanol from crude oil
    • Ethene is produced when crude oil fractions are cracked
    • Ethene is hydrated, water added across double bond
  • Ethene is mixed with steam (H2O(g)) and passed over a catalyst consisting of Silicon dioxide coated with phosphoric acid (H3PO4)
  • Hydration means addition of water to a compound
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13
Q

What is the conditions of the Hydration of ethene to produce ethanol

Raw materials (type), Type of process, Reaction rate, Purity of ethanol

A
  • Conditions: Temperature = 300ºC, Pressure = 70atm, Catalyst = conc phosphoric acid
  • Raw materials (type) : Crude oil (finite)
  • Type of process: Continuous
  • Reaction rate: Fast
  • Purity of ethanol: Pure
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14
Q

What can ethanol be used for and what is a biofuel

A
  • Can be burnt as a fuel (burned in excess oxygen to produce carbon dioxide and water)
  • C2H5OH + 3O2 →2CO2 + 3H2O
  • A biofuel is a fuel produced from biological resources
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15
Q

What is an advantage and disadvantage of fermentation of alcohols at 35ºC rather than 25ºC and What does carbon neutral mean

A
  1. Advantage: Ethanol is produced at a faster rate
  2. Disadvantage: More energy is used/ required in the reaction
  3. Carbon neutral - No net production of CO2 in the atmosphere
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16
Q
  1. Ethanol can be manufactured by the direct hydration of ethene and by the fermentation of sugars. What is meant by hydration?
  2. Give 1 advantage and 1 disadvantage of manufacturing ethanol by fermentation rather than hydration

How is Fermentation known to be Carbon neutral

A
  1. Addition of water/steam
  2. Advantage: Low technology, renewable feedstock, allowed for ususe in drinks, perfumes, considered to be green
  3. Disadvantage: Slow, low yield, significant land use, has to be distilled, labour intensive
17
Q

What is a redox reaction and What happens in reduction and oxidation

A
  • A redox reaction has a simultaneous reduction and oxidation reaction
  • Reduction:
    • Gain of H
    • Loss of O
  • Oxidation:
    • Gain of O
    • Loss of H
18
Q

What is Redox reaction in alcohols, what does an oxidising agent do and what is the common oxidising agent in oxidising alcohols

A
  • Alcohols can be oxidised to other products depending on the type of alcohol
  • A substance that oxidises another is called an oxidising agent
  • A common oxidising agent is acidified dichromate (VI) ions, (H+/Cr2O72-)
  • Often provided by sulfuric acid mixed with potassium dichromate solution
19
Q

In redox reactions in alcohols what happens to the Potassium dichromate ions

A
  • Potassium dichromate ions are orange
  • They can be reduced to green Chromium (III) (Cr3+)
  • This happens when the dichromate ions oxidise something else
  • This means they act as oxidising agents
20
Q

What happens when a Primary alcohol is oxidised

A
  • It produces an aldehyde and can be further oxidised to produce carboxylic acids
  • Oxidising ethanol to ethanal- excess alcohol, little oxidising agent - distillation remove product as it is made - stop from being oxidised further
  • Oxidising ethanol to ethanoic acid - conc sulfuric acid - excess dichromate used, mixture is refluxed, vapour condenses and drips back into the reaction flask, eventually all oxidised to acid. After 20mins distil ethanoic acid with water
21
Q

What happens when a secondary alcohol is oxidised

A
  • Ketones are produced and not oxidised further
22
Q

Why are tertiary alcohols not oxidised

A
  • Oxidation needs C-C bond not C-H bond
23
Q

What are aldehydes and ketones and their differences

A
  • Both have C=O group (carbonyl group) Aldehydes suffix -al and have carbonyl group at the end of the chain
  • Ketones have suffix one and have carbonyl group in the body
24
Q

What are the different tests to test for aldehydes or ketones

A
  • Tollens Reagent: Ammonical silver nitrate solution. (silver nitrate dissolved in ammonia)
    • Aldehydes produce a silver mirror effect inside the container. Ag(NH3)2+ +e-→Ag + 2NH3
    • Silver I complex reduced to Ag when aldehyde is oxidised
  • Fehlings Solution: Blue solution of Copper (II) ions dissolved in sodium hydroxide
  • Aldehydes reduce Cu2+ to a brick red Cu+ percipitate. The aldehydes oxidised to an acid Cu2+ e —> Cu+
25
Q

Outline a simple procedure to allow you to determine whether A is primary, secondary or tertiary alcohol

A
  • Mix the alcohol with warm acidified Potassium dichromate (K2CR207) - lack of reaction is tertiary alcohol
  • Distillation of initial product for 1 or 2
  • Effect on tollens reagent or fehlings solution on oxidation product identifies primary or secondary alcohol.
26
Q

How can alkenes be produced from alcohols

A
  • By acid catalysed elimination reactions
  • Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil.
27
Q

EXAM Q: Alcholic drink has methanol, ethanol, ethanal, ethanoic acid and phosphoric acid

  1. Identify how alcohol in the drink was produced
  2. Suggest a test to confirm presence of ethanal
  3. Explain how ethanal and ethanoic acid were produced from ethanol
A
  1. Hydration of ethene - phosphoric acid is only used in this technique
  2. Tollens/Fehlings/Benedicts turms silver with aldehydes or brick red percipitate
  3. Oxidation - ethanol excess with no reflux produces ethanal and water
  • Excess oxidising agent with reflux produces ethanoic acid
28
Q

What are elimination reactions

A
  • Molecule is removed (for example water) dehydration of alcohols is an elimination reaction
  • Water molecule made from -OH group and H next to this group
29
Q

What is the apparatus for an elimination reaction (dehydration) and what are the conditions

A
  • Elimination reactions remove small molecules
  • This is always water in alcohols
  • This forms alkens and Isomeric products can be produced (Aluminium oxide is used as a catalyst
  • Hot conc sulfuric or phosphoric acid at 180 degrees

A Level Chemistry: Organic Chemistry (12 decks)

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