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Chemistry A Level > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

General formula of alcohols

A

CnH2n+1OH

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2
Q

Functional group of alcohols

A

OH

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3
Q

Classifications

A

Primary, secondary, tertiary

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4
Q

What is primary butanol and its placement

A

Butan-1-ol, OH group end of chain

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5
Q

What is secondary butanol and its placement

A

Butan-2-ol, OH group on length of chain

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6
Q

What is tertiary butanol and its placement

A

2-methylpropan-2-ol, OH group on a branch on chain

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7
Q

What are alcohols boiling point compared to alkanes of similar relative molecular mass?

A

Higher due to hydrogen bonding between molecules (as well as van der waal) Alkanes only have van der waal Hydrogen bonding stronger

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8
Q

Hydrogen bonding drawing

A
  • Needs delta + and -
  • Lone pair
  • Label hydrogen bond
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9
Q

What are the various ways of forming alcohols?

A
  • Nucleophilic substitution of halogenoalkane
  • Hydration of alkenes (elimination)
  • Electrophillic addition of alkene with sulfuric acid followed by reaction with water
  • Fermentation
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10
Q

What is needed for nucleophilic sub of halogenoalkanes to form alcohols?

A

Reagent: NaOH or KOH Conditions: aqueous/warm (reflux) OH- ion

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11
Q

What are the conditions of a hydration of alkenes (industrial method) and equation

A

C2H4 + H20 —–> C2H5OH - Needs conc phosphoric acid absorbed on solid silica surface as catalyst - 60 atm pressure - 600K temp - excess ethane to give high yield

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12
Q

When does fermentation occur?

A

When yeast and bacteria convert sugars to alcohols, and acid and various gases such as carbon dioxide and methane

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13
Q

Conditions of fermentation to produce ethanol?

A
  • Yeast provides enzymes - Anaerobic respiration process/remove air - Temp 35 degrees - Aqueous solution (neutral) - Batch process/ uses renewable resources/ slow (days)
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14
Q

Equation of reaction of glucose to ethanol

A

C6H12O6 ——> 2C2H5OH + 2CO2 reaction will stop when alcohol level is about 14%

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15
Q

Uses of fermented alcohol

A
  • Wine/ beer (if alcoholic drinks need higher conc of alcohol, fractional distillation used) - Biofuels (made from living organisms or their waste)
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16
Q

Advantages of fermentation as alcohol production

A
  • Raw material is renewable and sustainable
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17
Q

Disadvantages of fermentation

A
  • Food supply is depleted as land is used to grow crops for fuel - Production of crops is subject to weather and climate - It takes time to grow crops and further processing is needed (like fractional distillation to seperate water and alcohol)
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18
Q

What is carbon neutral?

A

Activity in which there is no net annual emissions of CO2 into atmosphere

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19
Q

Example of carbon neutral fuel?

A

Bioethanol

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20
Q

Production of sugar equation

A

6CO2 + 6H20 —–> C6H12O6 + 6O2

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21
Q

Complete combustion of ethanol equation

A

C2H5OH + 3O2 ——> 2H2O + 3CO2

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22
Q

Incomplete combustion of ethanol equation

A

C2H5OH + 5O2 —–> 6H20 + 5CO

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23
Q

How does an alcohol form an alkene and what are the conditions needed?

A

Elimination (dehydration reaction) Conditions: Concentrated H2SO4 / 170 degrees or Al2O3 / 600 degrees

24
Q

OH group alcohols can

A

hydrogen bond to water molecules

25
Q

…cannot bond to water molecules

A

non-polar hydrocarbon chain

26
Q

Why are alcohols with short hydrocarbon chains soluble in water?

A

because hydrogen bonding predominates

27
Q

Why are alcohols with longer hydrocarbon chains insoluble in water?

A

Non-polar hydrocarbon chain dominates

28
Q

What is the benefit of making alcohols from a dehydration reaction?

A

Allows you to make alkenes from renewable resources i.e. without crude oil

29
Q

Elimination reaction Name the condition and product when an alcohol is used as a reactant

A

Product: alkene Al203 catalyst 450 K Concentrated hot H2SO4

30
Q

Ethanol + H2SO4 = Name mechanism

A

elimination

31
Q

Ethanol + H2SO4

Mechanism

A

elimination

32
Q

How does distillation work?

A

Uses the fact that chemicals have different boiling points and seperates them out to get a single purified substance

33
Q

Name two ways ethanol can be produced

A
34
Q

Describe hydration

A
  1. Hydration of ethene using steam to produce ethanol
  2. Acid catalyst
  3. High temperature + high pressure
  4. H20 added across double bond
35
Q

Hydration

Name 3 conditions for producing ethanol

A
36
Q

Describe fermentation

A

(exothermic reaction) is carried out by yeast in anaearobic respiration

Yeast produces sugars into ethanol and cabron dioxide

Ethanol formed is seperated by fractional distillation

37
Q

What is an advantage of using fermentation to make alcohol

A

Low tech process (uses cheap equipment and renewable resources)

38
Q

State the equation for hydration of ethene (including state symbols)

A
39
Q

Name 2 ways an alcohol can be oxidised

A
40
Q

Define oxidation

A

Loss of eectrons

Gain of oxygen

(Loss of hydrogen)

41
Q

Define reduction

A

Gain of electrons.

Loss of oxygen

(Gain of hydrogen)

42
Q

Define oxidising agent

A

Gain electrons

43
Q

What are primary alcohols oxidised to?

A

Aldehydes

44
Q

Describe how you would oxidise and alcohol to just get an aldehyde

A
  1. Gently heating alcohol with potassium dichromate (VI) and sulfuric acid in test tube = alcohol
  2. To just get alcohol distill it off immediately
45
Q

Describe how you would oxidise an alcohol to just get a carboxylic acid

A

Alcohol has to be vigorously oxidised:

alcohol mixed with excess oxidising agent and heated under reflux

46
Q

Explain how heating under reflux ensures the complete oxidation of an alcohol to a carboxylic acid

A

Any escaped vapour is condensed back into liquid

So any unreacted aldehyde can be oxidised/reduced further

47
Q

What are secondary alcohols oxidised into?

A

ketones

48
Q

Describe how you would oxidise a secondary alcohol into a ketone

A

Reflux a secondary alcohol with acidifed potassium dichromate (VI)

49
Q

State what colour changes occur when potassium dichromate (VI) is added to a primary, secondary and tertiary alcohol

A

Primary and secondary alcohol:

Orange —-> green

Tertiary alcohol:

No colour change - remains orange

50
Q

Explain why potassium dichromate (VI) turns from orange to green

A

Orange dichromate(VI) ion, Cr2O7(2-) is reduced to green chromium(III) ion, Cr3+

51
Q

Can tertairy alcohols be oxidised when reacting them with potassium dichromate (VI)

A

No

52
Q

Why can’t tertiary alcohols be oxidised by reacting them with potassium dichromate (VI)?

A

Because of a lack of hydrogen atoms on carbon atom which the hydroxyl group is attached to

53
Q

Explain why butanal has a lower boiling point than both butan-1-ol and butanoic acid

A

Dipole-dipole forces between butanal molecules where as there are hydrogen bonds in both other molecules

Dipole-dipole forces are weaker than hydrogen bonds as they require less energy to break

54
Q

Ethanol can be oxidised into ethanal, describe this reaction

A

Oxidising agent, 2 hydrogen atoms removed, forming water

55
Q

Describe what happens when an alcohol is heated uner reflux?

A
  1. Mixture of liquids heated to boiling point for prolonged time
  2. Vapour is formed which escapes from liquid mixture and is changed back into liquid + returned to liquid mixture
  3. Any alcohol and aldehyde that initally evaporates can be then oxidised

Chemistry A Level (25 decks)

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