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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
Why are tertiary alcohols not oxidised easily? | ketones not oxidised further for same reason
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)
26
What sort of smell do many aldehydes and ketones have?
pleasant smells
27
What solution is often used to oxidise alcohols to aldehydes and ketones?
solution of potassium dichromate, acidifies with dilute sulfuric acid
28
What is the oxidising agent when alcohols are oxidised to aldehydes and ketones?
the solution
29
When alcohols are oxidised to aldehydes and ketones, what happens to the dichromate (IV) ions?
orange dichromate (VI) ions reduced to green chromium (III) ions
30
What is used to oxidise ethanol (primary alcohol) to ethanal- an aldehyde?
dilute acid and less potassium dichromate (VI) than needed for complete oxidation to carboxylic acid used
31
What is done to the mixture? (oxidise ethanol (primary alcohol) to ethanal- an aldehyde)
heated gently
32
What is done to the receiver? (to oxidise ethanol (primary alcohol) to ethanal- an aldehyde)
cooled in ice to reduce evaporation of product
33
What happen to ethanal when it forms? (oxidise ethanol (primary alcohol) to ethanal- an aldehyde)
vaporises as soon as it's formed and distils off
34
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)
stops it from being oxidised further to ethanoic acid
35
What happen to unreacted ethanol? | oxidise ethanol (primary alcohol) to ethanal- an aldehyde
remains in flask
36
What is the notation [O] often used to represent?
oxygen from the oxidising agent
37
What is the equation for ethanol (primary alcohol) to ethanal- an aldehyde?
CH3CH2OH (l) + [O] = CH3CHO (g) + H20 (l)
38
What is used to oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid?
concentrated sulfuric acid + more than enough potassium dichromate (VI) used for complete reaction (dichromate (VI) in excess)
39
What is done to the mixture? (oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid)
refluxed
40
What does reflux mean?
vapour condenses and drips back into reaction flask
41
What happens while the reaction mixture is refluxing? (oxidise ethanol (primary alcohol) to ethanoic acid- carboxylic acid)
any ethanol or ethanal vapour will condense and drip back into the flask until, eventually, it's all oxidised to the acid
42
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)
after refluxing for around 20 minutes
43
What is the equation for oxidising ethanol (primary alcohol) to ethanoic acid- carboxylic acid?
CH3CH20H (l) + 2[O] = CH3COOH (g) + H20 (l)
44
What are secondary alcohols oxidised to ketones by?
acidified dichromate
45
What group do aldehydes and ketones both have?
C=O group
46
What is the C=O group called?
carbonyl group
47
Where is the carbonyl group in aldehydes?
at the end of the hydrocarbon chain
48
Where is the carbonyl group in ketones?
in the body of the hydrocarbon chain
49
What suffix are aldehydes usually names using?
suffix -al
50
What suffix are ketones usually names using?
suffix -one
51
Are the physical properties of ketones and aldehydes similar?
yes
52
What two tests can tell aldehydes and ketones apart?
Tollen's (silver mirror) test Fehling's test
53
What does the Tollen's test and Fehling's test both involve?
involve gentle oxidation
54
What are aldehydes oxidised to?
carboxylic acids RCHO + [O] = RCOOH
55
Are ketones changed by gentle oxidation?
no
56
What is Tollens's reagent? (hint- agent)
gently oxidising agent
57
What is Tollens's reagent? (what it's made of)
solution of silver nitrate in aqueous ammonia
58
What does Tollens's reagent do?
oxidises aldehydes
59
What does Tollens's reagent do to ketones?
no affect on ketones
60
What does Tollens's reagent contain?
colourless silver(I) complex ions, containing Ag+
61
What happens to the Ag+ ions in Tollens's reagent when aldehyde oxidised?
reduced to metallic silver Ag
62
What happens on warming an aldehyde with Tollens's reagent?
deposit of metallic silver formed on insides of test tube- silver mirror
63
What is the Fehling's reagent? (hint-agent)
gentle oxidising agent
64
What does Fehling's reagent contain?
blue copper (II) complex ions which will oxidise aldehydes but not ketones
65
What happens during oxidation with Fehling's reagent?
blue solution gradually changed to brick red precipitate of copper(I) oxide Cu2+ + e- -> Cu+
66
What happens on warming an aldehyde with blue Fehling's solution?
brick red precipitate gradually form

C15- ALCOHOLS (3 decks)

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