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AS Chemistry > Alcohols > Flashcards

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
Q

Why is a temperature of 35 needed in fermentation?

A

Because below 25 the reaction is too slow but above 40 the enzymes denature

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26
Q

When ethanol is formed after fermentation, what is done to it and why?

A

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

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27
Q

What are the disadvantages of fermentation/

A

Batch process (ineffiecient bc new equipment set up), very slow rate of reaction and impure ethanol produced which needs further purification

28
Q

What are the advantages of fermenation?

A

Uses a renewable source and uses gentle temp and pressure

29
Q

What are the disadvantages of hydration?

A

Uses finite sources and lot of energy to heat

30
Q

What are the advantages of hydration?

A

Continuous flow process (flow over a catalyst) so more efficient, fast and purer ethanol

31
Q

What is a biofuel?

A

Any fuel made from living organisms or their waste (biomass)

32
Q

Why may biofuel not actually be carbon neutral?

A

Production of fertilisers and pesticide requires energy, transportation of ethanol produces CO2 and fractional distillation of ethanol requires CO2

33
Q

Advantages of biofuel

A

Carbon-neutral and sustainable bc using renewable source of energy

34
Q

Disadvantages of biofuel

A

Food crops used for fuel - ethical issues
Food crops subject to climate
Growing crops takes time
Gotta purify the ethanol

35
Q

What is an example of an oxidising agent?

A

Acidified potassium dichromate (VI) solution

36
Q

What can the oxidation of a primary alcohol produce?

A

An aldehyde or a carboxylic acid

37
Q

What is the functional group of an aldehyde?

A

CHO

38
Q

How can you get an aldehyde from a primary alcohol?

A

Excess primary alcohol

Distill product immediately to prevent further oxidation

39
Q

How can you get a carboxylic acid from a primary alcohol?

A

Excess of acidified potassium dichromate solution

Reflux gently

40
Q

What is the product from the oxidation of a secondary alcohol?

A

A ketone

41
Q

What are the conditions for ketones to be formed?

A

Refluxed with excess potassium dichromate (VI) solution

42
Q

What is the functional group of a ketone?

A

CO

43
Q

Why can’t tertiary alcohols be oxidised?

A

Because they have no hydrogens attached to the carbon with the OH group attached

44
Q

What is the C=O group called?

A

Carbonyl group

45
Q

What is Tollen’s reagent?

A

A colourless solution of silver nitrate and dilute ammonia

46
Q

How does the silver mirror test work?

A

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
Q

What does Tollen’s reagent do in the presence of a ketone?

A

Does not react and the mixture stays colourless

48
Q

What is in Fehling’s 1?

A

Copper sulphate

49
Q

What’s in Fehling’s 2?

A

Sodium hydroxide

50
Q

How is Fehling’s used to test for aldehydes?

A

Heated with the aldehyde and the blue colour disappears and an orange-red precipitate of copper oxide is formed

51
Q

What is an elimination reaction?

A

Where a small molecule is removed from the reactant molecule

52
Q

What is a dehydration reaction?

A

When a molecule of water is eliminated

53
Q

What conditions are needed for the dehydration of alcohols?

A

Concentrated sulfuric acid catalyst at a temp. of 170 or alcohol vapour over heated aluminium oxide catalyst at 600C

54
Q

How are alcohols formed?

A

from the hydration of alkenes with an acid catalyst

55
Q

Explain what refluxing is?

A

The continuous boiling, evaporation and condensing of a mixture over a long period of time to ensure a reaction takes place

56
Q

Why do you add reactants slowly during reflux?

A

Because reaction is exothermic. Adding slowly dissipates the heat

57
Q

What are anti-bumping granules?

A

Small rough pieces of silica which provide a surface for gas bubbles to build up on - promotes smooth and even boiling

58
Q

Why is a vertical condenser needed in reflux?

A

To condense evaporated gases back into the reaction mixture - ensures no vapour escapes

59
Q

Why is there no stopper in the condenser in the reflux equipment?

A

So that the pressure doesn’t build up

60
Q

What is the purpose of distillation?

A

To separate products

61
Q

Which equations would you use to show that biofuel is carbon neutral?

A

photosynthesis
fermentation
combustion

62
Q

How do anti-bumping granules prevent violent boiling?

A

They provide a surface for gas bubbles to form - prevent large gas bubbles from building up

63
Q

Define carbon neutral

A

No net emission of CO2 into the atmosphere

64
Q

How can you make a more concentrated solution of ethanol from fermentation?

A

Fractional distillation

65
Q

Give an equation for the oxidation of a primary alcohol to an aldehyde

A

Primary alcohol + [O] —-> aldehyde + H2O

66
Q

Give an equation for the oxidation of a primary alcohol to a carboxylic acid

A

Primary alcohol + 2[O] —> carboxylic acid + H2O

67
Q

Give an equation for the oxidation of a secondary alcohol to a ketone

A

Secondary alcohol + {O] —-> ketone + H2O

AS Chemistry (14 decks)

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