Alcohol

Question 1

Hydration of ethene

Answer 1

Production of ethanol by the vapour phase hydration of ethene (from fossil fuels) in the presence of an acidic catalyst (H3PO4), CH2CH2 (g) + H20 (g) <—> CH3CH2OH Enthalpy= -45kJ (exothermic), 1 pass only yields around 5% ethanol meaning unreacted ethene is recycled and the process repeats to get around 95% conversion after 20 passes

Question 2

Optimal conditions for the hydration of ethene

Answer 2

Moderate temperature, High pressure, Phosphoric acid catalyst

Question 3

Steps of hydration of ethene

Answer 3

Excess ethene (shifts equilibrium forward) is mixed with steam at 300 degrees and 60-70 atm, Gases are cooled and become liquid, Distillation is used to purify ethanol (remove water), Some ethene remains a gas and is recycled

Question 4

Fermentation

Answer 4

Most commonly used (93%), * C6H12O6 (aq) –yeast–> 2 CH3CH2OH (aq) + 2 CO2 (g), CH3CH2OH is poison and kills off competitors however this means a yield of only 15% as the enzyme starts to die, Distillation is used to purify ethanol to 96%

Question 5

Fermentation ingredients and steps

Answer 5

Usually uses starches and sugars as raw materials but cellulose (found in biomass) can be used, Biomass is kept at a temperature of around 35 degrees until fermentation is complete as the yeast is living and a higher temperature would kill it, Oxygen mut be excluded to ensure anaerobic respiration and no further oxidation of the ethanol to ethanoic acid

Question 6

Temperature of fermentation vs hydration of ethene

Answer 6

Fermentation- low
Hydration- moderate (needs more energy)

Question 7

Pressure of fermentation vs hydration of ethene

Answer 7

Fermentation- normal
Hydration- high which increases cost

Question 8

Catalyst used in fermentation vs hydration of ethene

Answer 8

Fermentation- Amylase and cellulase help produce simple sugars and yeast enzymes for fermentation
Hydration- Phosphoric acid

Question 9

Purification of fermentation vs hydration of ethene

Answer 9

Fermentation- many distillations required which increases cost
Hydration- Limited distillation required

Question 10

Raw materials used in fermentation vs hydration of ethene

Answer 10

Fermentation- monosaccharides from grains and other plant materials
Hydration- Ethene from crude oil

Question 11

Fermentation vs hydration of ethene regarding renewable

Answer 11

Fermentation- yes, uses bio mass
Hydration- No

Question 12

Cost of fermentation vs hydration of ethene

Answer 12

Fermentation- low
Hydration- high

Question 13

Use of ethanol

Answer 13

Used for alcoholic beverages, solvents or biofuels, If not used in alcoholic beverages, can be sold as methylated spirits but is poisoned with methanol and pyridine (makes it taste bad)

Question 14

Green chemistry

Answer 14

Overarching philosophy related to sustainable and environmentally friendly chemical practices

Question 15

Principles of green chemistry (12)

Answer 15

Prevent waste, Maximise atom economy (contains maximum proportion of starting materials), Design less hazardous chemical syntheses, Design safer chemicals and products, Use safer solvents and reaction conditions, Increase energy efficiency, Use renewable raw materials (biomass), Avoid chemical derivatives (waste), Use catalysts instead of excess reactants, Design biodegradable chemicals and products, Analyse in real time to prevent pollution, Minimise the potential for accidents

Question 16

Primary alcohol

Answer 16

Carbon atatched to hydroxyl group is attached to one other carbon

Question 17

Secondary alcohol

Answer 17

Carbon attached to hydroxyl group is attached to two carbons

Question 18

Tertiary alcohol

Answer 18

Carbon attached to hydroxyl group is attached to three carbons

Question 19

Melting and boiling points of alcohol

Answer 19

Higher than the corresponding alkane, As chain length increases, melting and boiling point increases due to the increased molecular mass and dispersion forces, Primary > secondary > tertiary

Question 20

Comparison of different types of alcohol melting and boiling point

Answer 20

Primary alcohols of the same size as other alcohols have the highest boiling point as they have a large surface area, Tertiary alcohols have the lowest boiling point as they have a decreased surface area meaning they are harder to interact with

Question 21

Solubility of alcohol in water

Answer 21

Alcohols are soluble in water and small alcohols are infinitely soluble, As chain length increases, solubility in water decreases, In shorter chains the strongest intermolecular force is hydrogen bonds, In longer chains the strongest intermolecular force is dispersion forces which is weaker than the hydrogen bonding thus decreasing solubility

Question 22

Solubility of alcohol in organic solvents

Answer 22

Alcohols are not very soluble in organic solvents, As chain length increases, solubility increases due to dispersion forces

Question 23

Combustion reactions of alcohol

Answer 23

Redox reaction, Burn rapidly in air and are very exothermic, CH3CH2OH (l) + 3 O2 (g) —> 2 CO2 (g) + 3 H2O (g)

Question 24

Alcohols reaction with sodium

Answer 24

Alcohols are less acidic then water as they undergo less self-ionisation to produce hydrogen ions (2 OH + ROH <—> ROH2+ (alkanoxide) + RO-), Longer the chain, the slower the reaction, General formula- 2 Na + 2 ROH —> 2 Na+RO- + H2

Question 25

Oxidation of all alcohols

Answer 25

Oxidise with strong oxidising agents (acidified KMnO4 and K2Cr2O7), Aldehydes can be removed using distillation but assume they have not unless stated

Question 26

Oxidation of primary alcohols

Answer 26

Primary alcohols oxidise to at first form aldehydes and then further oxidise to carboxylic acid (RCH2OH —> RCHO —> RCOOH)

Question 27

Oxidation of secondary alcohols

Answer 27

Secondary alcohols oxidise to form ketones (can’t be acid due to the carbon-carbon bonds) (RCHOHR’ —> RCOR’)

Question 28

Oxidation of tertiary alcohols

Answer 28

Tertiary alcohols don’t react with potassium dichromate and potassium permanganate due to the carbon-carbon bond that can’t break