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Chem > Alcohols > Flashcards

Alcohols Flashcards

1
Q

Functional group in alcohol

A

OH
hydroxyl

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2
Q

Alcohols are either

A

Primary
Secondary or tertiary

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3
Q

Explain primary secondary and tertiary alcohols

A

Primary - this is when the carbon with OH group attached is attached to 1 carbon
Secondary - this is when the carbon with OH group attached is attached to 2 other carbons
Tertiary - this is when carbon with the OH group attached is attached to 3 other carbons

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4
Q

How to make alcohols to alkenes

A

Dehydration reaction
Elimination of water

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5
Q

General equation for dehydration

A

CnH2n+1OH —> CnH2n + H2O

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6
Q

How are alcohols produced?

A

Hydration of alkenes

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7
Q

Conditions for hydration

A

High temp (300•c)
High pressure (70atm)
Have to say concentrated Phosphoric acid catalyst or sulphuric acid

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8
Q

How can ethanol be produced

A

Fermentation of glucose
Hydration of ethene with steam

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9
Q

Advantages of hydration of ethanol with ethene

A

Faster production
Continuous process
Virtually pure product

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10
Q

Disadvantages of hydration of ethene

A

Ethene is non renewable - comes from crude oil fractions
Crude oil will run out and ethene will be expensive
And expensive initial costs

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11
Q

Is fermentation endo or Exothermic

A

Exothermic

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12
Q

Conditions of fermentation

A

Addition of yeast
Anaerobic conditions
Temp of 35 degrees

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13
Q

Equation for fermentation

A

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

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14
Q

Why is yeast added during fermentation

A

Yeast produces an enzyme which converts sugars such as glucose into ethanol and carbon dioxide

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15
Q

Why is temp of fermentation done in 35 degrees (30-40)

A

The enzyme works at this optimum temp
If too cold the reaction is slow
If too hot enzyme denatured damaged

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16
Q

In fermentation what happens when ethanol is formed

A

It’s separated from the rest of the mixture by fractional distillation

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17
Q

Advantages of fermentation

A

It’s low tech
Uses cheap equipment
Uses renewable resources (sugar)

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18
Q

Disadvantages of fermentation

A
  • The last fractional distillation step that’s needed to purify ethanol takes extra time and money
  • Batch process
19
Q

What kind of fuel is ethanol

A

Biofuel

20
Q

What is a biofuel

A

A fuel that’s been made from biological material (plants) that’s recently died

21
Q

Advantages of biofuel

A

Renewable energy resource - won’t run out so more sustainable
They’re carbon neutral (they produce co2 when burnt however plants take in same amount of co2 during photosynthesis)

22
Q

Disadvantages of biofuels

A

When switching from fossil fuel to biofuel in cars - they’re car engines would have to be modified to use fuels with high concentrations of ethanol
Land used to grow crops for fuel cannot be used to grow food
If countries use land to grow biofuel crops instead of food they may be unable to feed everyone in a country

23
Q

Explain why bioethanol (biofuel) is carbon neutral using equations

A

So burning biofuel produces CO2, the same amount of CO2 is taken in by plants when growing so bio ethanol carbon neutral

Plants take in carbon dioxide to produce glucose by photosynthesis…..
6CO2 + 6H2O —> C6H12O6 + 6O2 ….. 6 mol of co2 taken in from atomosphere to produce one mol of glucose

In fermentation process, glucose converted to ethanol …
C6H12O6 —> 2C2H5OH + 2CO2 … 2 mol of co2 rel into atmosphere when 1 mol of glucose converted to 2 mol of ethanol

When Ethanol is burned CO2 and water are produced…
2C2H5OH + 6O2 —> 4CO2 + 6H2O … 4 mol of CO2 released when 2 mol of ethanol are burned completely

So therefore If you combine all 3 equations exactly 6 mol of co2 are taken in and exactly 6 mol of co2 are given out

24
Q

Why isn’t fermentation method to produce bioethanol completely carbon neutral

A

Fossil fuels will need to be burnt to power the machinery used to make fertilisers for crops, harvest the crops and refine and transport the bioethanol, this produces co2. So using bioethanol made by fermentation isn’t completely carbon neutral.

25
Q

Describe the mechanism for formation of an alcohol by the reaction of an alkene with steam in presence of an acid catalyst

A

Starting with Ethene … curly arrow from double bond to H+
Leaves carbocation intermediate … curly arrow from lone pair on oxygen on H20 to carbocation
O has + Beneath it Arrow from middle of the O - H bond to the O with a + beneath it
Then alcohol is formed + H+ ion

26
Q

Hydration of Ethene equation

A

C2H4 + H2O —> CH3CH2OH
<—

27
Q

Equation for combustion of ethanol

A

2C2H5OH + 6O2 —> 4CO2 + 6H2O

28
Q

Why is ethanol as a biofuel carbon neutral

A

6 mol of co2 in during photo synthesis
2 mol of co2 out during fermentation plus 4 mol of co2 out during combustion
= 6 mol of co2 out
So no net release of co2

29
Q

Types of alcohols

A

Primary
Secondary
Tertiary

30
Q

What is a primary alcohol

A

The carbon attached to OH group is attached to one other carbon

31
Q

What is a secondary alcohol

A

The carbon attached to OH is attached to 2 other carbons

32
Q

What is a tertiary alcohol

A

The carbon attached to the OH group is attached to 3 other carbons

33
Q

What are products during oxidation of primary, secondary and tertiary alcohols

A

Primary - alcohols and carboxylic acids
Secondary - ketones
Tertiary - cannot be oxidised

34
Q

Oxidising agent for alcohols

A

Acidified potassium dichromate
K2Cr2O7

35
Q

Colour change for oxidation of alcohol

A

Orange to green when oxidation has occurred

36
Q

Oxidising agent represented as

A

[O]

37
Q

What is byproduct in oxidation of alcohol

A

H20

38
Q

When oxidising an alcohol eg ethanol into ethanal how do you stop it turning into carboxylic acid

A

To prevent into ethanooic acid you heat and distill
Condenser is diagonal

39
Q

When oxidising an 1 alcohol into ethanooic acid what apparatus do you use

A

Heat under reflux
Condenser is vertical

40
Q

Test for aldehydes

A

Tollens reagent (ammoniacal silver nitrate)
Aldehyde - silver mirror
Ketone - no change

41
Q

Fehlings solution

A

aldehydes - orange precipitate
Ketones - no change

42
Q

Dehydration cannot occur in alcohol if …

A

Carbon adjacent to carbon bonded to OH isn’t bonded to Any Hydrogens as H2O mol cannot be eliminated
Eg if carbon bonded to 3 methyl groups

43
Q

Define molecular ion

A

Molecule with one electron lost

Chem (15 decks)

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