Unit 2.7 Alcohols and carboxylic acids

Question 1

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

Answer 1

Steam and ethene are passed over a catalyst of phosphoric acid

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

Explain preparation of ethanol by fermentation

Answer 4

• 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

Question 5

What are biofuels?

Answer 5

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

Question 6

Ethical issue with biofuels?

Answer 6

• 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

Question 7

Economic issues with biofuels?

Answer 7

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

Question 8

Environmental issues with biofuels?

Answer 8

• 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

Question 9

Explain dehydration of ethanol?

Answer 9

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)

Question 10

How to identify primary alcohols? (1°)

Answer 10

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

Question 11

How to identify secondary alcohols? (2°)

Answer 11

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 - “

Question 12

How to identify tertiary alcohols? (3°)

Answer 12

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 - “

Question 13

How is an alcohol oxidised?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Ending remarks of primary alcohol oxidising?

Answer 16

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 ¬.¬

Question 17

Explain secondary alcohols (2°) oxidising?

Answer 17

• 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

Question 18

Explain tertiary alcohols (3°) oxidisng?

Answer 18

• 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

Question 19

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

Answer 19

Orange -> Green

Question 20

What colour change do u get when testing tertiary alcohols?

Answer 20

No colour change

Question 21

Explain hydrogen carbonate test for carboxylic acids?

Answer 21

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?)

Question 22

Explain carboxylic acids reaction with bases

Answer 22

• 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
CH_{3</sub<COOH(l) + NaOH(s) -> CH3COONa(aq) + H2O(l)}

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

Question 23

Explain carboxylic acids reaction with carbonates and hydrogencarbonates

Answer 23

• 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

Question 24

A test to identify carbon dioxide gas produced?

Answer 24

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

Question 25

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

Answer 25

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)

Question 26

How to name esters?

Answer 26

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

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

Question 27

Equipment needed for distillation?

Answer 27

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

Question 28

How does distillation work for producing esters?

Answer 28

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

Question 29

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

Answer 29

D: