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Y12 AS Chemistry > Ethanol production > Flashcards

Ethanol production Flashcards

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1
Q

What are the two ways to make ethanol?

A

Hydrating alkenes and fermenting sugars

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2
Q

What is the standard industrial method for producing alcohols?

A

Hydrate an alkene

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3
Q

What are the conditions for hydrating an ethene?

A

Hydrate using steam
Acid catalyst - solid phosphoric acid catalyst concentrated
300 degrees Celsius
60 atm

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4
Q

What is the general equation for a hydration of an alkene?

A

CnH2n + H2O + (acid catalyst) -> CnH2n+1OH

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5
Q

What is hydration the opposite mechanism of?

A

Dehydration

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6
Q

What is the equation for the hydration of ethene?

A

CH2=CH2 + H2O -> CH3CH2OH

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7
Q

Is the hydration of an alkene reversible or irreversible?

A

Reversible

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8
Q

Although the yield of the hydration of an alkene is low (5%), what can be done to improve this?

A

The unreacted ethene gas can be recycled which causes the yield to become 95%

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9
Q

Why will producing ethanol by fermentation become important in the future?

A

Ethene comes from crude oil and supplies may run out in the future

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10
Q

What type of process is fermentation?

A

Exothermic

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11
Q

What carries out fermentation?

A

Yeast in anaerobic conditions

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12
Q

What is the equation for fermentation?

A

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

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13
Q

What condition is needed for fermentation?

A

Anaerobic conditions

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14
Q

How does fermentation work?

A

The yeast produce enzymes which convert glucose into ethanol and carbon dioxide

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15
Q

What is the optimum temperature for the enzymes in fermentation to work at?

A

30-40 degrees celsius

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16
Q

What happens to the enzymes if the temperature is too high?

A

They will become denatured and the reaction will no longer work

17
Q

What happens if the temperature is too low?

A

The reaction will be too slow

18
Q

At what percentage of ethanol does the yeast die?

A

15%

19
Q

What is used to increase the concentration of the ethanol?

A

Fractional distillation

20
Q

What is the rate of reaction for the hydration of ethene?

A

Very fast

21
Q

What is the rate of reaction for fermentation?

A

Very slow

22
Q

What is the quality of the product from the hydration of ethene?

A

Pure

23
Q

What is the quality of the product from fermentation?

A

Very impure - needs further processing with fractional distillation which increases costs and time

24
Q

What is the raw material used in the hydration of ethene?

A

Ethene from oil which is a finite resource

25
Q

What is the raw material used in fermentation?

A

Glucose/sugars - renewable resource

26
Q

What is the process and the costs like for the hydration of ethene?

A

Continuous process
Expensive equipment needed
Low labour costs

27
Q

What is the process and the costs like for fermentation?

A

Batch process
Cheap equipment
High labour costs

28
Q

What is a biofuel?

A

A fuel thats made from biological material thats recently died

29
Q

What are advantages of using biofuel?

A

Biofuels are renewable resources
More sustainable
They only release the same amount of carbon dioxide that was taken in when the crop plant was growing - carbon neutral

30
Q

What are disadvantages of biofuel?

A
  • When land is being used to grow crops for fuel, it cant be being used to grow food
  • Trees may be cut down to create more land - deforestation destroys habitats and trees cut down are burnt which releases more carbon dioxide
  • Fertilisers are often added and this means that waterways can be polluted
  • Practical issues with switching from fossil fuels to biofuel
31
Q

What is carbon-neutral?

A

When the fuel is burnt produced from the plant only releases the same amount of carbon dioxide which they took in in the first place

32
Q

What are three equations to support the idea that ethanol as a biofuel is carbon neutral and explain them?

A

1 ) 6CO2 + H2O -> C6H12O6 + 6O2 (6 moles of carbon dioxide taken In to produce 1 mole of glucose during photosynthesis)

2) C6H12O6 -> 2C2H5OH + 2CO2 ( 2 moles of carbon dioxide are made when 1 mole of glucose is converted into 2 moles of ethanol)
3) 2C2H5OH + 6O2 -> 4CO2 + 6H2O (4 moles of carbon dioxide are made when 2 moles of ethanol are completely burned)

33
Q

What do the three equations show?

A

6 moles of CO2 are taken in and 6 moles are then given out = carbon neutral

34
Q

Why might ethanol as a biofuel not be carbon neutral?

A

Fossil fuels need to be burnt to power the machinery to make the fertilisers for the crops and power the machinery to harvest them.
Refining and transporting biofuels also needs energy

Y12 AS Chemistry (48 decks)

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