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C15- ALCOHOLS > 15.3- THE REACTION OF ALCOHOLS > Flashcards

15.3- THE REACTION OF ALCOHOLS Flashcards

1
Q

What must there be enough of for alcohols to burn completely?

A

enough oxygen available

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2
Q

What do alcohols burn completely to?

A

carbon dioxide and water

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3
Q

What happens when alcohols do not burn completely?

A

incomplete combustion- carbon monoxide or carbon produced

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4
Q

What is the equation for the complete combustion of ethanol?

A

C2H50H (l) + 302 (g) = 2CO2 (g) + 3H20 (l)

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5
Q

What is ethanol often used as?

A

fuel

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6
Q

Example of when ethanol is used a fuel?

A

in picnic stoves that burn methylated spirits

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7
Q

What is methylated spirits?

A

ethanol with a small percentage of poisonous methanol added to make it unfit to drink

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8
Q

Why is poisonous methanol added to methylated spirits?

A

so it can be sold without tax which is levied on alcoholic drinks

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9
Q

What dye is added to methylated spirits?

A

purple dye

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10
Q

Why is purple dye added to methylated spirits?

A

to show that it should not be drunk

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11
Q

What are elimination reactions?

A

ones in which a small molecule leaves the parent molecule

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12
Q

In the case of alcohol elimination reactions, what is the small molecule that leaves the parent molecule?

A

water

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13
Q

What is the water from the elimination reaction of alcohol made from?

A

-OH group and a hydrogen atom from the carbon next to the -OH group

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14
Q

So, what are the elimination reactions of alcohols always?

A

dehydration

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15
Q

What can alcohols be dehydrated with? (2)

A

excess hot concentrated sulfuric acid OR by passing their vapours over heated aluminium oxide

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16
Q

What is formed when an alcohol is dehydrated?

A

alkene

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17
Q

What is an alternative dehydrating agent?

A

phosphoric(V) acid

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18
Q

What type of reaction is combustion usually?

A

complete oxidation

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19
Q

How can alcohols be also oxidised?

A

gently and in stages

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20
Q

What are primary alcohols oxidised to?

A

aldehydes, RCHO

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21
Q

What can aldehydes be further oxidised to?

A

carboxylic acids, RCOOH

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22
Q

What are secondary alcohols oxidised to?

A

ketones, R2CO

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23
Q

Are ketones oxidised further?

A

no

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24
Q

Are tertiary alcohols oxidised easily?

A

no

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25
Q

Why are tertiary alcohols not oxidised easily?

ketones not oxidised further for same reason

A

because oxidation would need a C-C bond to break, rather than a C-H bond (which is what happens when an aldehyde is oxidised)

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26
Q

What sort of smell do many aldehydes and ketones have?

A

pleasant smells

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27
Q

What solution is often used to oxidise alcohols to aldehydes and ketones?

A

solution of potassium dichromate, acidifies with dilute sulfuric acid

28
Q

What is the oxidising agent when alcohols are oxidised to aldehydes and ketones?

A

the solution

29
Q

When alcohols are oxidised to aldehydes and ketones, what happens to the dichromate (IV) ions?

A

orange dichromate (VI) ions reduced to green chromium (III) ions

30
Q

What is used to oxidise ethanol (primary alcohol) to ethanal- an aldehyde?

A

dilute acid and less potassium dichromate (VI) than needed for complete oxidation to carboxylic acid used

31
Q

What is done to the mixture? (oxidise ethanol (primary alcohol) to ethanal- an aldehyde)

A

heated gently

32
Q

What is done to the receiver? (to oxidise ethanol (primary alcohol) to ethanal- an aldehyde)

A

cooled in ice to reduce evaporation of product

33
Q

What happen to ethanal when it forms? (oxidise ethanol (primary alcohol) to ethanal- an aldehyde)

A

vaporises as soon as it’s formed and distils off

34
Q

As the ethanal is vaporised and distils off as soon as it’s formed, what does this stop it from? (oxidise ethanol (primary alcohol) to ethanal- an aldehyde)

A

stops it from being oxidised further to ethanoic acid

35
Q

What happen to unreacted ethanol?

oxidise ethanol (primary alcohol) to ethanal- an aldehyde

A

remains in flask

36
Q

What is the notation [O] often used to represent?

A

oxygen from the oxidising agent

37
Q

What is the equation for ethanol (primary alcohol) to ethanal- an aldehyde?

A

CH3CH2OH (l) + [O] = CH3CHO (g) + H20 (l)

38
Q

What is used to oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid?

A

concentrated sulfuric acid + more than enough potassium dichromate (VI) used for complete reaction (dichromate (VI) in excess)

39
Q

What is done to the mixture? (oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid)

A

refluxed

40
Q

What does reflux mean?

A

vapour condenses and drips back into reaction flask

41
Q

What happens while the reaction mixture is refluxing? (oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid)

A

any ethanol or ethanal vapour will condense and drip back into the flask until, eventually, it’s all oxidised to the acid

42
Q

When can you rearrange the apparatus to distil off the ethanoic acid along with any water? (oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid)

A

after refluxing for around 20 minutes

43
Q

What is the equation for oxidising ethanol (primary alcohol) to ethanoic acid- carboxylic acid?

A

CH3CH20H (l) + 2[O] = CH3COOH (g) + H20 (l)

44
Q

What are secondary alcohols oxidised to ketones by?

A

acidified dichromate

45
Q

What group do aldehydes and ketones both have?

A

C=O group

46
Q

What is the C=O group called?

A

carbonyl group

47
Q

Where is the carbonyl group in aldehydes?

A

at the end of the hydrocarbon chain

48
Q

Where is the carbonyl group in ketones?

A

in the body of the hydrocarbon chain

49
Q

What suffix are aldehydes usually names using?

A

suffix -al

50
Q

What suffix are ketones usually names using?

A

suffix -one

51
Q

Are the physical properties of ketones and aldehydes similar?

A

yes

52
Q

What two tests can tell aldehydes and ketones apart?

A

Tollen’s (silver mirror) test

Fehling’s test

53
Q

What does the Tollen’s test and Fehling’s test both involve?

A

involve gentle oxidation

54
Q

What are aldehydes oxidised to?

A

carboxylic acids

RCHO + [O] = RCOOH

55
Q

Are ketones changed by gentle oxidation?

A

no

56
Q

What is Tollens’s reagent? (hint- agent)

A

gently oxidising agent

57
Q

What is Tollens’s reagent? (what it’s made of)

A

solution of silver nitrate in aqueous ammonia

58
Q

What does Tollens’s reagent do?

A

oxidises aldehydes

59
Q

What does Tollens’s reagent do to ketones?

A

no affect on ketones

60
Q

What does Tollens’s reagent contain?

A

colourless silver(I) complex ions, containing Ag+

61
Q

What happens to the Ag+ ions in Tollens’s reagent when aldehyde oxidised?

A

reduced to metallic silver Ag

62
Q

What happens on warming an aldehyde with Tollens’s reagent?

A

deposit of metallic silver formed on insides of test tube- silver mirror

63
Q

What is the Fehling’s reagent? (hint-agent)

A

gentle oxidising agent

64
Q

What does Fehling’s reagent contain?

A

blue copper (II) complex ions which will oxidise aldehydes but not ketones

65
Q

What happens during oxidation with Fehling’s reagent?

A

blue solution gradually changed to brick red precipitate of copper(I) oxide

Cu2+ + e- -> Cu+

66
Q

What happens on warming an aldehyde with blue Fehling’s solution?

A

brick red precipitate gradually form

C15- ALCOHOLS (3 decks)

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