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Chemistry > CH15 Alcohols > Flashcards

CH15 Alcohols Flashcards

1
Q

Functional group of an alcohol

A

Hydroxyl group -OH

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2
Q

General formula

A

CnH2n+1OH

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3
Q

Prefix and suffix of naming alcohols

A

Hydroxyl- or -OH

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4
Q

Intermolecular forces do alcohols have - why

A

Hydrogen bonding - electronegativity difference in OH bond

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5
Q

Alcohols MP and BP compared to hydrocarbons of similar C chain lengths - why

A

Higher - hydrogen bonding is stronger than van der Waals forces

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6
Q

Are alcohols soluble in water - why does solubility depend on chain length

A

Soluble when short chain - OH hydrogen bonds to hydrogen bond in water
Insoluble when long chain - non-polarity of C-H bond takes precedence

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7
Q

What makes a primary alcohol

A

C bonded to OH is only bonded to 1 other C atom

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8
Q

What makes an alcohol secondary

A

C bonded to OH is bonded to 2 other C atoms

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9
Q

What makes an alcohol tertiary

A

C bonded to OH is bonded to 3 other C atoms

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10
Q

How can ethanol be made from crude oil

A

Hydration of ethene via electrophilic addition

phosphoric acid catalyst

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11
Q

What are the advantages and disadvantages of this method

A

Advantages - fast, continuous process, ethanol ha a high purity
Disadvantages - not renewable as from crude oil

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12
Q

How can ethanol be made by fermentation

A

Plant carbohydrates broken down and fermented in yeast –> ethanol

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13
Q

What conditions are needed for this reaction to take place

A

Enzymes in yeast as catalyst, 3 degrees C, anaerobic conditions

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14
Q

Equation for this reaction

A

C6H12O6 (aq) –> 2C2H5OH + 2CO2

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15
Q

Advantages and disadvantages of this method

A

Advantages - renewable as from plants
Disadvantages - slow, batch process, enzymes stop working at 15% alcohol so solution is not pure, needed to be fractionally distilled

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16
Q

In the future, how might most ethene be made - why is it not made like this at the moment

A

Dehydrate ethanol made by fermentation

Not economically viable

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17
Q

Define carbon neutral

A

No net addition of CO2 to the atmosphere - carbon dioxide released when combusted = carbon dioxide absorbed as a plant

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18
Q

Explain how using ethanol in petrol engines could be considered to be carbon neutral

A

Carbon dioxide released in fermentation and combustion = carbon dioxide absorbed when growing

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19
Q

Why would it probably not be entirely carbon neutral to use ethanol

A

Other “carbon costs” associated with it (transport)

20
Q

What is a commercial fuel that uses ethanol? What else does it contain and why

A

Methylated spirits - methanol

21
Q

Equation for combustion of ethanol

A

C2H5OH (l) 3O2 (g) –> 2CO2 (g) + 3H2O (l)

22
Q

What is an elimination reaction

A

The removal of a smaller molecule from a larger one

23
Q

Which group leaves the parent molecule in the case of alcohols

A

OH and a H

24
Q

What physical conditions needed for the elimination reaction from alcohols to alkenes

A

Excess hot concentrated sulphuric acid or pass vapour of hot aluminium oxide

25
Q

What forms if you partially oxidise a primary alcohol

A

An aldehyde

26
Q

What conditions are needed to partially oxidise a primary alcohol

A

Dilute sulphuric acid, potassium dichromate (VI), distill product as it’s produced, gentle heating

27
Q

Equation for partial oxidation of ethanol

A

CH3CH3OH (l) + [O] –> CH3CHO (g) + H2O (l)

28
Q

What forms if you fully oxidise a primary alcohol

A

A carboxylic acid

29
Q

What conditions are needed for this reaction

A

Concentrated sulphuric acid
Potassium dichromate (VI)
Reflux
Strong heating

30
Q

Equation for full oxidation of ethanol

A

CH3CH2OH (l) + 2[O] –> CH3COOH (g) + H2O (l)

31
Q

What forms if you oxidise a secondary alcohol

A

Ketone

32
Q

Why can it not be oxidised further and why can’t a tertiary alcohol be oxidised

A

A C-C bond would have to break

33
Q

What conditions are needed for the oxidation of a secondary alcohol

A

Concentrated sulphuric acid
Potassium dichromate (VI)
Reflux
Strong heating

34
Q

Equation for oxidation of propan-2-ol

A

CH3CH(OH)CH3 (l) + [O] –> CH3COCH3 (g) + H2O (l)

35
Q

What is an aldehyde - functional group

A

Molecule with C=O (carbonyl) group at the end of a carbon chain

36
Q

Suffix of aldehydes

A

-al

37
Q

What is a ketone - functional group

A

Molecule with C=O (carbonyl) group in the middle of carbon chain

38
Q

Suffix of ketones

A

-one

39
Q

What is a carboxylic acid - functional group

A

Molecule with COOH (carboxyl) group at the end of a carbon chain

40
Q

Suffix of carboxylic acids

A

-oic acid

41
Q

What does Tollen’s test give a positive result for

A

Aldehydes

42
Q

What is in Tollen’s reagent

A 
Silver nitrate in NH3 (aq) - oxidises aldehydes but not ketones
Complex silver (I) ions reduced to Ag (s)
43
Q

Result of the Tollen’s test for aldehydes and ketones

A

Aldehydes - silver mirror forms

Ketones - no visible change

44
Q

What does Fehling’s solution give a positive result for

A

Aldehydes

45
Q

What is in Fehling’s reagent

A 
Blue copper (II) complex ions - gentle oxidising agent
Reduced to Cu+ ions (brick red)
46
Q

Conditions needed with Fehling’s solution

A

Heat

Chemistry (18 decks)

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