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Alcohols Flashcards

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1
Q

What are the functional groups of alcohols?

A

OH

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2
Q

What is the general formula of alcohols?

A

CnH2n+2

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3
Q

What type of series are alcohols?

A

Homologous

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4
Q

What are primary alcohols?

A

An alcohol with the carbon with the OH group only has one other carbon attached to it

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5
Q

What are secondary alcohols?

A

An alcohol with two carbons attached to the carbon with the OH group

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6
Q

What are tertiary alcohols?

A

Alcohols with three carbons attached to the carbon with the OH group

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7
Q

What are the two types of intermolecular forces between alcohol molecules?

A

Van der Waals forces and hydrogen bonding

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8
Q

Where are van der Waals forces present in alcohols?

A

Along the carbon chain of the alcohol

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9
Q

Why are van der Waals forces weaker in secondary and tertiary alcohols?

A

Their structures mean that they can’t lie as closely together

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10
Q

Where are hydrogen bonds present in alcohols?

A

Between the lone pair on the oxygen of one OH group of one molecule and the hydrogen in the OH group of another molecule

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11
Q

Why can hydrogen bonding be found in alcohols?

A

Because the OH groups are polar so there’s an attractive force between them

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12
Q

How can we increase the strength of the van der Waals forces?

A

Increasing the chain length

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13
Q

Which is stronger; hydrogen bonding or van der Waals forces?

A

Hydrogen bonding

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14
Q

What must happen before an alcohol can boil?

A

Enough energy has to be transferred from the surroundings to overcome intermolecular forces

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15
Q

Why are alcohols stronger than alkanes?

A

Alcohols have van der Waals and hydrogen bonding but alkanes just have van der Waals forces

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16
Q

Why are short chain alcohols soluble in water?

A

Because of the OH group

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17
Q

Why are alkanes insoluble in water?

A

Because they don’t have the OH group

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18
Q

What are the two ways in which ethanol can be produced?

A

Hydration of ethene and fermentation of glucose

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19
Q

What is the equation for the hydration of ethene?

A

C2H4 + H20 —> C2H5OH

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20
Q

What are the conditions used in hydration of ethene?

A

600K
pressure of 6000-7000Pa
phosphoric(V) acid catalyst in silica pellets
excess ethene for high yield

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21
Q

What is the equation for the fermentation of glucose?

A

C6H12O6 —-> 2C2H5OH + 2CO2

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22
Q

What are the conditions used in fermentation?

A

Absence of oxygen, presence of yeast and sugar solution and a temperature of 37-40

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23
Q

Why is yeast needed?

A

To produce enzymes which convert sugars into methanol

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24
Q

Why are anaerobic conditions needed in fermentation?

A

To prevent oxidation of ethanol into ethanoic acid

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25
Why is a temperature of 35 needed in fermentation?
Because below 25 the reaction is too slow but above 40 the enzymes denature
26
When ethanol is formed after fermentation, what is done to it and why?
Yeast is killed by ethanol of a too high % of ethanol so it's removed from the reaction mixture by fractional distillation and used to make biofuel
27
What are the disadvantages of fermentation/
Batch process (ineffiecient bc new equipment set up), very slow rate of reaction and impure ethanol produced which needs further purification
28
What are the advantages of fermenation?
Uses a renewable source and uses gentle temp and pressure
29
What are the disadvantages of hydration?
Uses finite sources and lot of energy to heat
30
What are the advantages of hydration?
Continuous flow process (flow over a catalyst) so more efficient, fast and purer ethanol
31
What is a biofuel?
Any fuel made from living organisms or their waste (biomass)
32
Why may biofuel not actually be carbon neutral?
Production of fertilisers and pesticide requires energy, transportation of ethanol produces CO2 and fractional distillation of ethanol requires CO2
33
Advantages of biofuel
Carbon-neutral and sustainable bc using renewable source of energy
34
Disadvantages of biofuel
Food crops used for fuel - ethical issues Food crops subject to climate Growing crops takes time Gotta purify the ethanol
35
What is an example of an oxidising agent?
Acidified potassium dichromate (VI) solution
36
What can the oxidation of a primary alcohol produce?
An aldehyde or a carboxylic acid
37
What is the functional group of an aldehyde?
CHO
38
How can you get an aldehyde from a primary alcohol?
Excess primary alcohol | Distill product immediately to prevent further oxidation
39
How can you get a carboxylic acid from a primary alcohol?
Excess of acidified potassium dichromate solution | Reflux gently
40
What is the product from the oxidation of a secondary alcohol?
A ketone
41
What are the conditions for ketones to be formed?
Refluxed with excess potassium dichromate (VI) solution
42
What is the functional group of a ketone?
CO
43
Why can't tertiary alcohols be oxidised?
Because they have no hydrogens attached to the carbon with the OH group attached
44
What is the C=O group called?
Carbonyl group
45
What is Tollen's reagent?
A colourless solution of silver nitrate and dilute ammonia
46
How does the silver mirror test work?
Tollen's reagent added to aldehyde and warmed gently, oxidising aldehyde to a carboxylic acid. Silver ions are reduced to atoms which are deposited on the sides to create a silver mirror effect.
47
What does Tollen's reagent do in the presence of a ketone?
Does not react and the mixture stays colourless
48
What is in Fehling's 1?
Copper sulphate
49
What's in Fehling's 2?
Sodium hydroxide
50
How is Fehling's used to test for aldehydes?
Heated with the aldehyde and the blue colour disappears and an orange-red precipitate of copper oxide is formed
51
What is an elimination reaction?
Where a small molecule is removed from the reactant molecule
52
What is a dehydration reaction?
When a molecule of water is eliminated
53
What conditions are needed for the dehydration of alcohols?
Concentrated sulfuric acid catalyst at a temp. of 170 or alcohol vapour over heated aluminium oxide catalyst at 600C
54
How are alcohols formed?
from the hydration of alkenes with an acid catalyst
55
Explain what refluxing is?
The continuous boiling, evaporation and condensing of a mixture over a long period of time to ensure a reaction takes place
56
Why do you add reactants slowly during reflux?
Because reaction is exothermic. Adding slowly dissipates the heat
57
What are anti-bumping granules?
Small rough pieces of silica which provide a surface for gas bubbles to build up on - promotes smooth and even boiling
58
Why is a vertical condenser needed in reflux?
To condense evaporated gases back into the reaction mixture - ensures no vapour escapes
59
Why is there no stopper in the condenser in the reflux equipment?
So that the pressure doesn't build up
60
What is the purpose of distillation?
To separate products
61
Which equations would you use to show that biofuel is carbon neutral?
photosynthesis fermentation combustion
62
How do anti-bumping granules prevent violent boiling?
They provide a surface for gas bubbles to form - prevent large gas bubbles from building up
63
Define carbon neutral
No net emission of CO2 into the atmosphere
64
How can you make a more concentrated solution of ethanol from fermentation?
Fractional distillation
65
Give an equation for the oxidation of a primary alcohol to an aldehyde
Primary alcohol + [O] ----> aldehyde + H2O
66
Give an equation for the oxidation of a primary alcohol to a carboxylic acid
Primary alcohol + 2[O] ---> carboxylic acid + H2O
67
Give an equation for the oxidation of a secondary alcohol to a ketone
Secondary alcohol + {O] ----> ketone + H2O

AS Chemistry (14 decks)

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