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a level chemistry > Alcohol production > Flashcards

Alcohol production Flashcards

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1
Q

Wha

A
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2
Q

What will we produce if we react Z-pent-2-ene with water?

A

pentan-2-ol or pentan-3-ol

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3
Q

These are examples of

A

addition reactions bcs we are adding a molecule (water) can also be called hydration reaction

& when a molecule loses water it’s a dehydration reaction

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4
Q

How do industries carry out hydration reaction?

A
  1. they add the alkene in its gas phase into the reactor
  2. they add water in the form of steam (g)
  3. add an acid catalyst (H+) to start the reaction
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5
Q

What can sulfuric acid act as?

A

electrophile

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6
Q

What happens if we react propene with water using sulfuric acid as our catalyst knowing that sulfuric acid acts as an electrophile?

A

carbon carbon bond breaks and a carbon hydrogen bond forms
causing H-O to break
making the electron pair go to Oxygen making it a long pair

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7
Q

Between these 2 molecules (propen-2-ene and propen-1-ene) what molecule would likely form

A

First molecule (propen-2-ene) as secondary carbocations are more stable than primary carbocations meaning the secondary carbocation would form majority of the time

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8
Q

Knowing that secondary is more stable, what would happen next in the mechanism?

A

because we are also reacting water
a water bond would form between the carbocation like this
arrow telling us C—O bond forms

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9
Q

What happens next after water bonds with the molecule of propene

A

The Lone pair attracts one of the H+ ions and forms a bond breaking the H—O bond

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10
Q

The complete mechanism memorise

from propene to propan-2-ol

A
  1. catalyst H forms a bond with the double bond of carbon forming a carbocation
  2. carbocation forms a bond with water
  3. lone pair of catalyst forms a bond of one Hydrogen and that hydrogen breaks the bond with oxygen
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11
Q

Because sulfuric acid is a reagent at the beginning of the reaction and a product at the end, its acting as a

A

catalyst

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12
Q

because H2SO4 (sulfuric acid) is acting as an electrophile, this is an example

A

of electrophilic addition reaction

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13
Q
A

mechanism of all reactions using sulfuric acid

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14
Q

How do we simplify this to make it easier rather than writing whole sulfuric acid out?

A

H+

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15
Q

What’s the most appropriate mechanism for this reaction?

A

As the acid wasn’t specified this is the correct answer

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16
Q

What’s wrong with this mechanism?

A

1) arrow is the other way around
2) Oxygen is missing a lone pair
3) Oxygen is missing a + bcs it has 3 bonds

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17
Q

What’s the equation for this reaction

A

CH2=CHCH2CH2CH3+H2O <=> CH3CH(OH)CH2CH2CH3

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18
Q

What’s the equation for the hydration of butene?

A

C4H8 + H2O <=> C4H9OH

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19
Q

What do we do when writing equations for ethene, propene and ethanol?

A

we just write their molecular formula as they don’t have position isomer

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20
Q

What’s the equation for the hydration of propene to propan-1-ol

A

C3H6 + H2O <=> CH3CH2CH2OH

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21
Q

Industries use a degree of 300 celsius which is a compromised temperature why is that so?

A

this reaction is exothermic as stated (-45 kJmol)
so if we lower the temperature the equilibrium position will shift to the right
and increase the yield of ethanol
However low temperatures also decrease the rate of reaction so industries use 300 as a compromise between yield and rate

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22
Q

Why does ethanol form in this reaction?

& when does it form a liquid

A

because of the high temperature which causes the ethanol to come out as a gas
it forms a liquid when it leaves the reactor and enters the condenser when it’s a liquid

23
Q

To produce ethanol from ethene industries use

A

H3PO4 (phosphoric) as a catalyst
compromised Temperature of 300
compromised Pressure if 6000 kPA

24
Q

What’s the equation for the hydration of ethene?

A

C2H4 + H2O <=> C2H5OH

25
Q

What’s the equation for the hydration of but-2-ene to butan-2-ol?

A

A

26
Q

which of these molecules is the major product in the dehydration reaction of pent-1-ene?
and why

A

C
to form pentan-1-ol, a primary carbocation intermediate must form. however to form pentan-2-ol, a secondary carbocation must form.

27
Q

what do catalyst do industries use to produce ethanol from ethene.
what are the conditions?

A

catalysts use Phosphoric acid H3PO4
they use compromised temperatures between 300 and 600
and compromised pressures between 5000 and 10000

28
Q

Why do industries use compromised temperatures and pressure when producing ethanol from ethene?

A

The higher the pressure, the more dangerous the conditions, the higher the yield of ethanol, the more expensive the conditions
The higher the temperature, the lower the ethanol yield, the faster the rate of reaction, the more expensive the conditions

The reaction of ethene with water is exothermic. industries use a compromised temperature for ethanol because high temperatures increase the rate of reaction but lower the yield of ethanol.
In the reaction of ethene with water, there are 2 moles of reactants and one mole of product. Industries use a compromise pressure because high pressure increase the yield of ethanol but they also increase the risk of explosion

29
Q

How can else can ethanol be produced?

A

By fermentation where ethanol can be produced from sugar
To produce ethanol from sugar we add warm water to sugar and add a single cell fungus (yeast) and make sure that there’s no oxygen in the system so we seal the mixture
we call ethanol produced from fermentation a biofuel

leave the mixture to produce ethanol and carbon dioxide

30
Q

why do we can ethanol produced from fermentation a biofuel?

A

because it’s made from biological resources

31
Q

What’s the sugar called in fermentation?

A

Sucrose

32
Q

When sucrose is added to warm water what does it break into?

A

it breaks into 2 molecules

glucose and fructose

33
Q

Out of the sugars it broke down in,

what forms ethanol in the process of fermentation?

A

glucose reacts to form ethanol and carbon dioxide

34
Q

What is the balanced equation for fermentation?

A
35
Q

What in yeast makes the glucose break down

A

enzymes produce by yeast catalyst reaction of glucose to produce ethanol and carbon dioxide

36
Q

Above a certain concentration, ethanol is toxic to yeast. So what concentration do we need?

A

To keep our yeast alive and working we need a low concentration of ethanol
We do this by removing ethanol when it’s formed.

37
Q

What can we use to seperate ethanol from the reaction?

A

distillation,
because ethanol has a lower boiling point than our sugars solution. We seperate ethanol from out reaction mixture using distillation

38
Q

What do we need to ensure during fermentation?

A

that there’s no oxygen present in the system

fermentation is carried out in the absence of oxygen

39
Q

What are the conditions of fermentation reactions?

A

we carry them out in the absence of water and keep the temperatures between 25-40 degrees celsius

40
Q

Ethanol produced by hydration is made from

A

crude oil which is a non renewable fossil fuel

41
Q

ethanol produced from fermentation is made from

A

plants which are renewable

42
Q

Why is the equipment used for fermentation much cheaper?

A

to produce ethanol from hydration we need to extract it from the ground, then undergoes fractional distillation and then cracked which are all expensive requirements

whereas to produce ethanol from fermentation we just need to grow and harvest the plants and produce yeast

so overall fermentation is much cheaper equipment wise

43
Q

Compared to fermentation, why is hydration less sustainable?

A

Fermentation only requires plants which won’t run out, whilst hydration requires crude oil which will run low
so fermentation is more sustainable

44
Q

Compared to hydration and fermentation, which one is energy sufficient

A

hydration requires temperatures of 300 C and 6000 kPA
whereas fermentation only requires 25-40 degree and standard pressure conditions
meaning we need far less energy to manage fermentation and cost will be way cheaper

45
Q

What are the advantages of hydration compared to fermentation?

A

Temperatures used for fermentation (25-40) is much lower than hydration (300) meaning hydration will have a higher rate of reaction so hydration produces ethanol quicker than fermentation (slower)

when we produce ethanol from fermentation we produce ethanol and carbon dioxide whereas if we produce ethanol from hydration we just produce ethanol meaning hydration has a higher atom economy (100%) so hydration is more efficient at producing ethanol than fermentation ( <100%)

when fermentation (batch process) is being done we need to clean it each time so we need to manually stop and keep going & only collect ethanol in batches 
whereas hydration when ethene is added to water in the reactor n reacts with acid catalyst ethanol is seperated and condensed and any remaining ethene or steam returns to the reactor so it means it can run continuously without stopping
hydration = continuous process which is another reason why its faster
46
Q

compare fermentation and hydration,

what process is better?

A

fossil fuel will run out

in the long term fermentation is better

47
Q

what’s the molecular form for glucose

A

C6H12O6

48
Q

when fuels completely combust what does it form?

A

CO2 and H2O

49
Q

What is carbon neutral defined as in terms of biofuels

A

No overal CO2 emission into the atmosphere

50
Q

What’s the equation for photosynthesis

A

6CO2 + 6H2O —> C6H12O6 + 6O2

51
Q

What’s the equation of fermentation

A

C6H12O6 —> 2C2H5OH + 2CO2

52
Q

What’s the equation for complete combustion

A

2C2H5OH + 6O2 —> 4CO2 + 6H2O

53
Q

What if we combine all photosynthesis, fermentation and complete combustion equation what would it look like ?

A

bcs of the repeat Carbon dioxide
bio-ethanol is carbon neutral

but in reality it’s not completely due to CO2 being released during fertiliser production, when it’s transported and when plants are harvested

54
Q

state the meaning of the term biofuel

A

biological resources 

a level chemistry (12 decks)

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