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A-Level Organic Chemistry AQA (Paper 2) > Alcohols > Flashcards

Alcohols Flashcards

1
Q

How do you obtain ethanol?

A

•From fermentation of sugars in fruits.

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2
Q

What is the general formula of alcohols? (2)

A
  • CnH2n+1OH.

* Can be shortened to ROH.

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3
Q

What is the functional group of alcohols?

A

•-OH.

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4
Q

How do you name alcohols? (5)

A
  • ‘Suffix-ol’
  • Name the main carbon chain.
  • The prefix hydroxy- is used if other functional groups are present.
  • Add a number to show where -OH group is.
  • Add prefix if there are more than one -OH group.
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5
Q

What is propane-1,2,3-triol known as?

A

•Glycerol- obtained from fats and oils found in living organisms.

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6
Q

What is the shape of alcohols? (2)

A

•The oxygen atom has two bonding pairs of electrons and two lone pairs.
•The C-O-H angle is 104.5 degrees.
(See textbook page 231)

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7
Q

What are primary alcohols? (Draw a diagram)

A

•The carbon with the -OH group has one R group.

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8
Q

What are secondary alcohols? (Draw a diagram)

A

•The -OH group is attached to a carbon with two R groups and only one hydrogen atom.

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9
Q

What are tertiary alcohols? (Draw a diagram) (2)

A
  • Three R groups are attached to the carbon that is bonded to the -OH group.
  • There are no hydrogen atoms bonded to this carbon.
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10
Q

What does the -OH group of alcohols mean for the physical properties of alcohols? (2)

A
  • Hydrogen bonding occurs between the molecules- alcohols have higher melting and boiling points than alkanes of similar relative molecular mass.
  • -OH group can hydrogen bond to water molecules, but the non-polar hydrocarbon chain cannot.
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11
Q

Why are alcohols with short hydrocarbon chains soluble in water?

A

•The hydrogen bonding predominates.

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12
Q

Why are alcohols with longer hydrocarbon chains insoluble in water?

A

•The non-polar hydrocarbon chain dominates.

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13
Q

Why are alcohols important in industrial chemistry? (2)

A
  • They are used as intermediates.

* They are easily made and easily converted into other compounds.

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14
Q

What are intermediates?

A

•Materials used to make other products.

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15
Q

What is the formula for ethanol?

A

•C2H5OH.

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16
Q

What is ethanol used as? (3)

A
  • An intermediate in the manufacture of other organic chemicals.
  • A solvent in cosmetics e.g. aftershave and perfume.
  • To manufacture drugs, detergents, inks and coatings.
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17
Q

How is ethanol made industrially? (3)

A

•By reacting ethene (made from the cracking of crude oil fractions) with steam, using a catalyst of CONC phosphoric acid/H3PO4 at 300 degrees Celcius and 60atm.
•Ethene is hydrated, water is added across the double bond.
CH2=CH2 + H2O -(phosphoric acid (catalyst))-> C2H5OH
•A non-renewable process.

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18
Q

Draw hydration mechanism of ethene to produce ethanol. (3)

A

•1). Arrow going from the double bond to H^+ ion (from water) —> carbocation (positive charge on carbon atom).
•2). Arrow going from the lone pair on O^delta negative (H2O molecule hydrogens are delta positive) —> positive charge on the oxygen atom.
•3). Arrow going from O-H bond to O^+ —> C2H5OH + H^+ (lone pair on oxygen atom).
(See textbook page 233)

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19
Q

How is ethanol made from sugars? (2)

A
  • Fermentation- a renewable process (carbohydrates come from crops such as sugar cane and sugar beet).
  • Conditions - enzymes from yeast and anaerobic.
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20
Q

Describe the process of making ethanol by fermentation. (4)

A

•Carbohydrates from plants are broken down into sugars and then converted into ethanol by the action of enzymes from yeast.
•Breakdown of a sugar: anaerobic respiration:
C6H12O6 (aq) (glucose) -enzyme from yeast-> 2C2H5OH (aq) (ethanol) + 2CO2 (g) (carbon dioxide).
•Air is kept out of the fermentation vessels to prevent oxidation of ethanol to ethanoic acid.
•Once the fermentation solution contains about 15% ethanol, the enzymes are unable to function and fermentation stops.

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21
Q

What is the rate of anaerobic respiration/fermentation affected by?

A

•Temperature- the temperature is compromised to 35 degrees Celcius to prevent denaturation of enzymes from yeast at high temp, too low = too slow.

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22
Q

How do you get ethanol from the fermentation solution?

A

•By distillation- ethanol has a boiling point of 78 degrees celcius (less than water, 100 degrees celcius).

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23
Q

What is the rate of reaction of making ethanol from crude oil (cracking and hydration)?

A

•Fast.

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24
Q

What is the rate of reaction of making ethanol from carbohydrates (sugars) (fermentation and distillation)?

A

•Slow.

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25
Q

What type of process is cracking and hydration?

A

•Continuous.

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26
Q

What type of process is fermentation and distillation?

A

•Batch.

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27
Q

What is the purity of ethanol produced from cracking and hydration?

A

•Essentially pure.

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28
Q

What is the purity of ethanol produced from fermentation and distillation?

A

•An aqueous solution of ethanol.

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29
Q

What is ethanol made by fermentation sometimes termed as?

A

•A carbon-neutral fuel.

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30
Q

What does it mean to be carbon neutral? (2)

A
  • The carbon dioxide released when the fuel is burnt is balanced by the carbon dioxide absorbed by the plant from which it was originally obtained during photosynthesis.
  • Net emission of carbon dioxide is 0.
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31
Q

What are elimination reactions? (3)

A
  • Ones in which a small molecule leaves the parent molecule.
  • In the case of alcohols, the ‘small’ molecule is always water.
  • The water is made from the -OH group and a hydrogen atom from the carbon next to the -OH group.
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32
Q

What are elimination reactions of alcohols always?

A

•Dehydrations.

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33
Q

How can alcohols be dehydrated? (4) (conditions for elimination)

A

•With excess hot concentrated sulfuric acid (catalyst).
•Or by passing their vapours over heated aluminium oxide.
•An alkene is formed.
CnH2n+1OH —> CnH2n + H2O

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34
Q

Draw the mechanism for the dehydration of propan-1-ol.

A

(See textbook page 235)

Elimination

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35
Q

What is an alternative dehydrating agent?

A

•Phosphoric (V) acid (H3PO4).

36
Q

Draw and label a diagram of the apparatus used for the dehydration of an alcohol. (5)

A 
•Ceramic fibre soaked in the alcohol.
•Heat.
•Aluminium oxide granules. 
•Product in a test tube.
•Water. 
(See textbook page 235).
37
Q

Draw the dehydration (elimination) mechanism of butan-2-ol and all of its products.

A

•Products: Z-but-2-ene, E-but-2-ene, but-1-ene.

38
Q

What are primary alcohols oxidised to? (2)

A
  • Aldehydes, RCHO.

* R = alkyl group.

39
Q

What are aldehydes oxidised to?

A

•Carboxylic acids, RCOOH.

40
Q

Draw the basic structure of an aldehyde.

A

•R-C(double bond to O, a carbonyl)-H.

41
Q

Draw the basic structure of a carboxylic acid.

A

•R-C(double bond to O, a carbonyl)-OH.

42
Q

What are secondary alcohols oxidised to?

A

•Ketones, R2CO or RCOR.

43
Q

Can ketones be oxidised further?

A

•No.

44
Q

Why are tertiary alcohols not easily oxidised? (2)

A
  • Oxidation would need a C-C bond to break rather than a C-H bond.
  • Ketones aren’t oxidised for the same reason.
45
Q

Draw the basic structure of a ketone.

A

•R-C(double bond to O, a carbonyl)-R.

46
Q

What is oxidation?

A

•The addition of oxygen to a species.

47
Q

What is something that adds oxygen?

A

•An oxidising agent.

48
Q

How do you represent an oxidising agent? (2)

A
  • [O]

* Oxygen is being produced by an oxidising agent.

49
Q

What is the main oxidising agent of alcohols? (3)

A

•Acidified potassium dichromate.
•H^+ (aq)/K2Cr2O7 (aq)
Or
•H^+ (aq)/Cr2O7^2- (aq) (the K ion is a spectator ion).

50
Q

What colour is acidified potassium dichromate?

A

•Yellow/orange colour.

51
Q

What happens to potassium dichromate if oxidation occurs? (2)

A
  • It goes from orange to green.

* Cr^6+ is reduced to Cr^3+ (green colour).

52
Q

Draw an equation to show the oxidation of ethanol. (2)

A

•Oxidation to ethanal (aldehyde).
•Oxidation of ethanal to ethanoic acic (carboxylic acid).
(See textbook page 236)

53
Q

Draw an equation to show the oxidation of propan-2-ol to propanone.

A

•Oxidation to propanone (ketone) and water.

54
Q

What is a solution of potassium dichromate acidified with?

A

•Dilute sulfuric acid.

55
Q

Write an equation (use structural formula) of the oxidation of ethanol to ethanal.

A

CH3CH2OH (l) + [O] —> CH3CHO (g) + H2O (l)

56
Q

Write an equation (use structural formula) of the oxidation of ethanol to ethanoic acid. (2)

A

CH3CH2OH (l) +2 [O] —> CH3COOH (g) + H2O (l)

•Twice as much oxidising agent is used because oxidation occurs twice.

57
Q

How are secondary alcohols oxidised to ketones?

A

•By acidified dichromate.

58
Q

How do you test for an aldehyde?

A

•Using Fehling’s test or Tollens’ test.

59
Q

What is Tollen’s reagent solution? (4)

A
  • A gentle oxidising agent.
  • A solution of silver nitrate in aqueous ammonia.
  • It oxidises aldehydes but has no affect on ketones.
  • It contains colourless silver (I) complex ions, contains Ag^+, which are reduced to metallic silver, Ag, as the aldehyde is oxidised.
60
Q

What is Fehling’s and Benedict’s reagent? (4)

A

•A gentle oxidising agent.
•It contains blue copper (II) complex ions which will oxidise aldehydes but not ketones.
•During oxidation, the blue solution gradually changes to a brick red precipitate or copper (I) oxide:
Cu^2+ + e^- —> Cu^+

61
Q

Outline the mechanism for the elimination of water from ethanol. (4)

A

•1). A lone pair of electrons from the oxygen bonds to a H^+ from the acid. The alcohol is pronated, giving the oxygen a positive charge.
•2). The positively charged oxygen pulls electrons away from the carbon. A H2O molecule leaves, creating an unstable carbocation intermediate.
•3). The carbocation loses a H^+.
•4). Alkene is formed.
(See revision guide page 148)

62
Q

What is distillation? (2)

A
  • Used to separate chemicals.

* The technique that uses the fact that different chemicals have different boiling points to separate them.

63
Q

Describe the process of distillation of producing cyclohexene from cyclohexanol. (5)

A
  • 1). Add concentrated H2SO4 and H3PO4 to a round bottomed flask containing cyclohexanol.
  • 2). Mix the solution by swirling the flask and add 2-3 carborundum boiling chips.
  • 3). The mixture is heated gently to around 83 degrees Celcius (the boiling point of cyclohexene) using a water bath or electric heater.
  • 4). Chemicals with boiling points up to 83 degrees Celcius will evaporate and rise out the flask first and into the condenser, which has cold water running through the outside, turning it into a liquid.
  • 5). The product can then be collected in a cooled flask.
64
Q

Why are carborundum chips added?

A

•To make the mixture boil more calmly, they prevent the bubbles from forming.

65
Q

Draw a diagram for the distillation apparatus set up. (10)

A
  • Reaction mixture.
  • Condenser.
  • Water out.
  • Water in.
  • Heat.
  • Round-bottomed flask.
  • Impure product.
  • Cooled flask.
  • Thermometer.
  • No lid.
66
Q

Describe the process of separation and purification (after distillation of cyclohexanol to cyclohexene). (5)

A
  • 1). The product collected after distillation will still contain impurities- transfer the product to a separating funnel and add water to dissolve water soluble impurities and create an aqueous solution.
  • 2). Allow the mixture to settle in lays, drain the aqueous layer, leaving the impure cyclohexene.
  • 3). Drain the cyclohexene in the round bottomed flask.
  • 4). Add anhydrous CaCl2 (a drying agent) and stopper the flask.
  • 5). Let the mixture dry for at least 20 minutes with occasional swirling and the cyclohexene will have small amounts of impurities so distil the mixture one last time.
67
Q

Describe the process of oxidising a primary alcohol to an aldehyde. (Ethanol) (Distillation) (2)

A
  • 1). Gently heat excess ethanol with potassium dichromate (VI) and sulfuric acid in a test tube produces ethanal (aldehyde).
  • 2). To get the aldehyde, use the distillation apparatus to get it out of the oxidising solution before it is oxidised to form ethanoic acid.
68
Q

Describe the reflux process of oxidising a primary alcohol to a carboxylic acid. (3)

A
  • 1). The primary alcohol is vigorously oxidised- it is mixed with excess oxidising agent and heated under reflux.
  • 2). Heating under reflux means you increase the temperature of an organic reaction without losing volatile solvents, reactants or products.
  • 3). Any vaporised compounds cool, condense and drip back into the reaction mixture- the aldehyde stays in the reaction mixture and is oxidised to carboxylic acid.
69
Q

Draw a diagram for the reflux apparatus setup. (7)

A
  • Water out.
  • Liebig condenser.
  • Water in.
  • Round bottomed flask.
  • Anti-bumping granules.
  • Heat.
  • Lid.
70
Q

Why is there no lid for distillation?

A

•It would explode.

71
Q

Why is a bunsen burner never used to heat the reaction mixture? (2)

A
  • You can’t control the temperature.

* Alcohols are flammable.

72
Q

Chloroethane reacts with ethanolic potassium cyanide under reflux, describe the following steps of the mechanism. (4)

A
  • 1). The C^delta positive attracts a lone pair of electrons from the CN^- ion.
  • 2). The CN^- ion acts as a nucleophile, attacking the slightly positive carbon atom.
  • 3). A new bond forms between the C and the CN^- ion, making a nitrile.
  • 4). The C-Cl bond breaks and both the electrons from the bond are taken by the Cl.
73
Q

Explain why chlorofluorocarbons entering the atmosphere where ultraviolet light breaks down C-Cl bonds to form chlorine free radicals is a problem. (Chlorine free radicals are regenerated)

A

•O3 absorbs the UV light radiation, which acts as a sunscreen and increases the chances of sunburn.

74
Q

Explain why the reaction of iodoethane with aqueous sodium hydroxide would proceed more quickly than with bromoethane and water?

A

•C-I has a lower bond enthalpy which is easier to break, C-Br has a higher bond enthalpy.

75
Q

When NaOH(aq) is dissolved in warm ethanol instead of water, how does this affect the type of reaction that occurs with bromoethane?

A

•Lone pair OH^- acts as a base (elimination reaction).

76
Q

Explain why the production of ethanol can be made important in the future.

A

•It is made from renewable resources, which are more important as amounts of crude oil decreases.

77
Q

Define the term biofuel.

A

•A fuel made from biological material that’s recently died.

78
Q

What is the symbol equation for photosynthesis?

A

6CO2 + 6H2O –light + chlorophyll–> C6H12O6

79
Q

What are the environmental factors surrounding biofuels? (3)

A
  • They aren’t carbon neutral, manufacturing still uses fossil fuels.
  • Fertilisers used to grow crops produce nitrous oxides, contributing to the greenhouse effect.
  • Deforestation takes place for land to grow crops.
80
Q

What are the ethical issues that surround biofuels? (2)

A
  • It decreases food resources, as land isn’t used to grow crops for food.
  • It increases the prices of palm oil and foods that use palm oil as there will be higher a demand for the biofuel used in transport.
81
Q

Why is production of ethanol via hydration of ethane essentially pure?

A

•Gases are passed over the catalyst several times = recycling of unreacted ethene.

82
Q

Write an equation for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.

A

2C(s) + 3H2(g) 1/2O2(g) —-> C2H5OH(l)

83
Q

What happens when the pressure is increased a lot in the hydration of ethane, it reacts to form a solid of a Mr of greater than 5000. Identify this solid.

A

•Poly(ethene).

84
Q

Gaseous ethanol can be used to convert copper (II) oxide into copper. Draw the structure of the organic compound with Mr = 60 that is produced in this reaction.

A

•CH3COOH, ethanol gets oxidised.

85
Q

How do you maximise the yield obtained in a distillation reaction? (2)

A
  • Keep the temperature of the reaction mixture below the boiling point of the desired product.
  • Cool the distillate in a collecting vessel.

A-Level Organic Chemistry AQA (Paper 2) (17 decks)

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