C Unit 2.7 Alcohols and Carboxylic acids Flashcards

1
Q

Chemical formula for industrial preparation of ethanol from ethene?
(hydration)

A

Steam and ethene are passed over a catalyst of phosphoric acid

CH2=CH2(g) + H2O(g) ⇌ CH3CH2OH(g) △H = -45 KJ mol-1

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2
Q

Ways to increase yield for industrial preparation of ethanol from ethene?

A

300°C - reaction is exothermic ∴ high yield would favour a low temp but reaction would be slow

Pressure of 60-70 atms - 2 moles of gas are converted into 1 mole of gas. High pressure favour high yield. However very high pressure required specialised and very expensive equipment

Phosphoric acid catalyst - just increases rate or reaction

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3
Q

How to make industrial preparation of ethanol from ethene for efficient conversion?

A
  • Steam and ethene recycled
  • Only about 5% conversion per pass
    (Theoretical atom economy is 100%)
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4
Q

Explain preparation of ethanol by fermentation

A
  • Sugar (glucose) from plant material
  • Is converted into ethanol and carbon dioxide
  • Takes place at temperatures of around 30°c
  • Enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen:
    C6H12O6 -> 2C2H5OH + 2CO2
  • Carbon dioxide escapes as a gas
  • Ethanol must be separated from the remaining liquid mixture
  • Boiling temp of ethanol = 80°C
  • ∴ separate from aqueous mixture through fractional distillation

Process widely used to produce ethanol for alcoholic drinks or bioethanol as a fuel for motor vehicles

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5
Q

What are biofuels?

A

A fuel that is produced through contemporary biological processes:
- Agriculture
- Anaerobic digestion

Rather than fuel produced by geological processes:
- Formation of fossil fuels such as:
Coal and petroleum, from prehistoric biological matter

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6
Q

Ethical issue with biofuels?

A
  • Crops can be used to feed people are instead being used to provide raw materials for bio fuels
  • Cause food shortages/increases price of food
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7
Q

Economic issues with biofuels?

A

Human resources - more people are needed to produce biofuels than are needed to produce petrol and diesel

Increased income - for farmers

Lower fuel prices - biofuels limit the demand for fossil fuels, helping to reduce increases in fuel prices

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8
Q

Environmental issues with biofuels?

A
  • Naturally contains little sulfur
  • Said to be carbon neutral:
    Amount of CO2 released when used is same as amount absorbed by plants as they
  • If so, reduces production of this greenhouse gas
  • However they produce less CO2 overall
  • Not carbon neutral
  • Cuz fossil fuels are used in their production e.g. making fertilisers
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9
Q

Explain dehydration of ethanol?

A

Many alcohols may be dehydrated to form an alkene:
CH3CH2OH(g) -> H2O(g) + CH2=CH2(g)

Reaction can be performed in lab by:
passing ethanol vapour over heated aluminium oxide

Alternatively the alcohol may be heated with concentrated sulfuric acid (in excess) at about 170°C:
CH3CH2CH2OH(g) -> CH3CH=CH2(g) + H2O(g)

Propan-1-ol w/ concentrated sulfuric acid = propene + water (steam)

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10
Q

How to identify primary alcohols? (1°)

A

Carbon which carries the -OH group only attached to one alkyl group (maximum of one other carbon)
e.g.
ethanol - no diagram…
propan-1-ol - “
2-methyl-propan-1-ol - “

  • Don’t matter how complicated the attached alkyl group is
  • Each case there’s only one linkage to an alkyl group from the CH2 group holding the -OH group

Exception:
Methanol, CH3OH, counted as a primary alcohol even though no alkyl groups attached to the carbon with the -OH group on it

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11
Q

How to identify secondary alcohols? (2°)

A

Carbon with the -OH group attached is joined directly to two alkyl groups(2 other carbons atoms), which may be same or different
e.g.
propan-2-ol - no diagram
butan-2-ol - “
pentan-3-ol - “

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12
Q

How to identify tertiary alcohols? (3°)

A

Carbon atom holding the -OH group is attached directly to three alkyl groups (3 other carbon atoms), which may be any combination of some or different
e.g.
2-methyl-propan-2-ol - no diagram ¬.¬
2-methyl-butan-2-ol - “

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13
Q

How is an alcohol oxidised?

A

Oxidising agent:
- Sodium
- Potassium dichromate(VI) acidified with dilute sulphuric acid

If oxidation occurs, orange solution reduced to green solution
Dichromate(VI) ions -> chromium(III) ions

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14
Q

Stage 1 of primary alcohol oxidising?
(ethanol -> ethanal (aldehyde))

A

Hydrogen atoms are lost - one from the OH and one from the adjacent carbon. This creates the carbon-oxygen double bond (a carbonyl bond)

On the edge of these groups:
From C-OH -> C-C=O & C-H (them 2 are together, if u know u know)

C2H5OH + [O] -> C2H4O

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15
Q

Stage 2 of of primary alcohol oxidising?
(aldehyde (ethanal) -> Carboxylic acid (ethanoic acid))

A

The aldehyde is oxidised further:

On the edge of these groups:
From C-C=O & C-H (if u know u know) -> C-C=O & C-OH

C2H4O + [O] -> C2H4O2

-> = reflux

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16
Q

Ending remarks of primary alcohol oxidising?

A

Primary alcohols can form aldehydes if you distill the product immediately after formation (diagram 2), the carboxylic acid will form if the alcohol is refluxed (diagram 1)

Refer to pg. 10 of booklet ¬.¬

17
Q

Explain secondary alcohols (2°) oxidising?

A
  • Oxidised to ketones (and that’s it)
    E.g.
  • Heat secondary alcohol propan-2-ol
    w/ sodium/potassium dichromate (VI) solution acidified with dilute sulphuric acid
  • Propanone formed

Playing around with the reaction condition s makes no difference whatsoever to the product

H-C-C-C-H + [O] -> H-C-C-C-H + H2O

1st one’s second C has OH above (propan-2-ol)
2nd one’s second C has C=O above (ketone/propanone/acetone ) if u know u know

18
Q

Explain tertiary alcohols (3°) oxidisng?

A
  • Aren’t oxidised by acidified sodium/potassium dichromate(VI) solution
  • Therefore no reaction whatsoever
  • The oxidising agent usually removes hydrogen from -OH group
  • And a hydrogen from the carbon atom attached to the -OH
  • Tertiary alcohols don’t have a hydrogen atom attached to that carbon
19
Q

What color change do u get when testing primary/secondary alcohols?

A

Orange -> Green

20
Q

What colour change do u get when testing tertiary alcohols?

A

No colour change

21
Q

Explain hydrogen carbonate test for carboxylic acids?

A

Sodium hydrogen carbonate is a chemical opposite of a carboxylic acid that will react producing a salt, carbon dioxide and water
(Acid + metal carbonate -> “)

If you pour some dilute ethanoic acid onto some white sodium carbonate or sodium hydrogen carbonate crystals, there is an immediate fizzing as a carbon dioxide is produced. You end up with a colourless solution of sodium ethanoate:

CH3COOH + NaHCO3 -> CH3COONa + CO2 + H2“O
Ethanoic acid + Sodium hydrogen carbonate -> Sodium ethanoate + Carbon dioxide + water

(S’pose relate to MASH?)

22
Q

Explain carboxylic acids reaction with bases

A
  • Simple neutralisation reactions
  • Same as another other reaction which hydrogen ions from an acid react with hydroxide ions

If you mix dilute ethanoic acid with sodium hydroxide solution, for example, you simply get a colourless solution containing sodium ethanoate. The only sign that a change has happened is that the temperature of the mixture will have increased (no visible change)

acid + alkali -> salt + water
CH3 CH3COONa(aq) + H2O(l)

For bases (ethanoic acid + copper(II) oxide):
CH3COOH(l) + CuO(s) -> C(H3COO)2Cu + H2O(l)
acid + base -> salt + water

23
Q

Explain carboxylic acids reaction with carbonates and hydrogencarbonates

A
  • Salt formed with carbon dioxide and water

If you pour some dilute ethanoic acid onto some white sodium carbonate or sodium hydrogencarbonate crystals, there is an immediate fizzing as carbon dioxide is produced. You end up with a colourless solution of sodium ethanoate (as discussed in carboxylic acids w/ bases)

C2H5CO2H + K2CO3 -> 2CH3CH2COOK + CO2 + H2O

or CH3CH2COOH or C2H5COOH

24
Q

A test to identify carbon dioxide gas produced?

A

Pass gas through lime water, if solution milky it’s present

25
Q

Explain esterification
(It’s more about the chemical formula, but obviously better to understand basic principles)

A

When an alcohol and a carboxylic acid react, they form a compound known as an ester (a sweet-smelling substance) and a small molecule (usually water). Sulfuric acid is used as a catalyst and the mixture is **heated to about 70°C*. The reaction is reversible

Ethanol + Ethanoic acid ⇌ Ethyl ethanoate + Water
I wish i can add visuals
(low-key just like biology… right?)
ester function group -> -C-O- (above C is =O)

26
Q

How to name esters?

A

e.g.
methanol + propanoic acid -> methyl propanoate + water

First part of the name comes from the alcohol
Second part from the carboxylic acid

27
Q

Equipment needed for distillation?

A
  • Round bottom flask
  • Reflux condenser
  • Ain’t there more????
28
Q

How does distillation work for producing esters?

A

First from basic:
- Distillation apparatus heats up the reaction mixture
- Substance with lowest boiling point (often the target molecule)
- Condensed and collected as the distillate

To make small ester (ethyl ethanoate):
1. Gently heat a mixture of ethanoic acid and ethanol
in the presence of concentration sulphuric acid
2. Distill off the ester as soon as it is formed

  • Prevents the reverse reaction happening
  • Works well cuz ester has lowest boiling point of anything present
  • Ester only thing in mixture which doesn’t form hydrogen bonds
  • Has weakest intermolecular forces
29
Q

I don’t feel too good about this one :v

A

D:

30
Q

Refresher

A

????