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Chemistry Y12 > O- Alcohols > Flashcards

O- Alcohols Flashcards

1
Q

State + explain the C-O-H bond angle in ethanol.

A

104
- repulsion betw. 2 lone pairs on O
- C-O & O-H bonds pushed closer tgt

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2
Q

What types of IMF do you expect to find between molecules of pentan-1-ol?

A
  1. H bonds
  2. vdW (C-H bonds)
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3
Q

Explain whether methanol and hexanol will dissolve in water.

A

ability to dissolve in water depends on ability to form H bonds w/ water
- methanol dissolves- ↑ polar ∵shorter hydrocarbon chain (OH takes up larger portion)
- hexanol x dissolve- longer non-polar alkyl chain

water = polar –> only dissolves polar

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4
Q

What happens to solubility of alcohols as the length of carbon chain increases?

A

↓
- ↑ vdW
- ↓ H bonding character

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5
Q

Uses of ethanol

A
  1. fuel
  2. cosmetics
  3. drinks industry
  4. antiseptics
  5. perfumes
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6
Q

What are the 2 methods of forming ethanol?

A
  1. hydration of ethene
  2. fermentation of glucose
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7
Q

Name the process that crude oil must undergo before it is able to be used.

A

Fractional distillation

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8
Q

Name the process used to form ethene after fractional distillation.

A

Cracking

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9
Q

What is hydration?

A

adding water (across a double bond)

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10
Q

Conditions for hydration of ethene.

A
  1. conc H3PO4 (used in industry)- catalyst
  2. steam
  3. high pressure
  4. 300oC

conc H2SO4 can also be used but H3PO4 in industry

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11
Q

What is the raw material for hydration of ethene?

A

crude oil

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12
Q

State the overall equation for hydration of ethene.

A

C2H4 (g) + H2O (g) –> C2H5OH(l)

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13
Q

Advantages for hydration of ethene.

A
  1. faster synthesis
  2. continual process
  3. purer product
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14
Q

Disadvantages for hydration of ethene.

A
  1. non-renewable (crude oil)
  2. ↑ energy costs (↑temp etc.)
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15
Q

What is the raw material for fermentation of glucose?

A

plants

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16
Q

How is the raw material processed in fermentation of glucose?

A
  • amylolytic enzymes
  • break down starch –> glucose
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17
Q

State the overall equation for fermentation of glucose.

A

C6H12O6 (aq) –> 2C2H5OH (aq) + 2CO2 (g)

18
Q

Conditions for fermentation of glucose.

A
  1. yeast
  2. anaerobic (prevent ethanol being oxidised into ethanoic acid)
  3. 35oC- compromise (↓ temp = ↓ rate; ↑ temp = enzymes denature)
19
Q

Does fermentation of glucose have a 100% atom economy?

A

x
- ethanol = desired product
- CO2 formed alongisde

20
Q

When the reaction stop in fermentation of glucose + what happens next?

A
  • when solution contains 15% ethanol –> enzymes stop functioning
  • ethanol separated from miture by fractional distillation —to purify
  • ∵ bp of water & ethanol are diff.

bp of ethanol ¬ 78oC

21
Q

Advantages of fermentation of glucose.

A
  1. renewable
  2. ↑ environmentally friendly
  3. low tech
  4. carbon neutral
  5. milder conditions (↓ temp + pressure)
22
Q

Disadvantages of fermentation of glucose.

A
  1. non-continual process
  2. ↓ pure product
23
Q

Give 2 examples of oxidation

A
  1. combustion
  2. rusting
24
Q

What is oxidation?

A
  • gain of O2
  • loss of e-
25
Q

What oxidises alcohols?

A

oxidising agent:
acidified potassium dichromate H+/K2Cr2O7

26
Q

How do you know an alcohol has been oxidised?

A

solution: orange –> green

27
Q

Outline steps of primary alcohol oxidation.

A

Repeat oxidation:
1. alcohol ‘OH’ — H+/ K2Cr2O7—> aldehyde ‘CHO’
2. aldehyde —H+/ K2Cr2O7—> carboxylic acid ‘COOH’

eg. ethanol–>ethanal–>ethanoic acid

28
Q

What could be the problem of repeat oxidation?

A

when we only want to form one of the products (aldehyde/ carboxylic acid)–> ways to control reaction

29
Q

How do we control oxidation of a primary alcohol?

A
  • aldehyde (singular oxidation)- H+/ K2Cr2O7 + distillation
  • carboxylic acid (further)- H+/ K2Cr2O7 + reflux
30
Q

Setup + keypoints for distillation

A
  • closed system w/ thermometer
  • heating mantle (instead of bunsen burner)- ethanol is v. flammable
  • anti-bumping granules- ✔ even boiling, prevent large bubbles
  • iced water (conical flask containing distillate submerged in)- so aldehyde product x evaporate
31
Q

What is reflux?

A
  • mixture of liquids
  • heated to bp
  • for a long time

used when substance has low bp/ volatile

32
Q

How does reflux work?

A
  • vapour formed escapes from the reaction vessel
  • converted back into a liquid- condenses as it gets cooler further up the Liebig condenser
  • so any ethanol/ ethanal evaporated ✔ oxidised
33
Q

Outline secondary alcohol oxidation.

A
  • alcohol —H+/ K2Cr2O7—> ketone ‘one’ (=O)
  • eg. CH3CH(OH)CH3 –> CH3C(O)CH3
    only singlar oxidation
    ∵ repeat oxidation would involve breaking a C-C bond- too strong
34
Q

Outline tertiary alcohol oxidation

A

x be oxidised
* ∵ would involve breaking a C-C bond- too strong

35
Q

What is lost from alcohol in alcohol elimination?

A

H2O- dehydration

36
Q

What is the reagent for alcohol elimination?

A

conc. H2SO4

37
Q

What are the conditiona for alcohol elimination?

A
  1. 600K
  2. Al2O3 catalyst
38
Q

Outline what happens in alcohol elimination.

A
  1. lone pair on O move to H+
  2. C-O bond breaks–> e- move to e- deficient O (+)
  3. C-H bond breaks–> C=C forms
  4. alkene
39
Q

Is alcohol elimination selective in forming products?

A
  • x selectivity
  • ∵ go via carbocations
40
Q

Test for carboxylic acid

A
  • react w/ carbonate
  • bubbles of CO2
41
Q

Why is it hard to distinguish between aldehydes and ketones?

A

look + react v. similarly

42
Q

Chemical tests to distinguish between aldehydes & ketones

A

separate mixtures of aldehyde & ketone
1. Tollens reagent- silver mirror formed vs x visible change//
2. warmed in Fehlings reagent- blue –> brick-red vs x visible change

Fehling’s is blue ∵ Cu2+ ions

Chemistry Y12 (33 decks)

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