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A Level Organic Chemistry > 3.5 Alcohols > Flashcards

3.5 Alcohols Flashcards

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1
Q

What is the functional group of an alcohol?

A

Hydroxyl group -OH

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2
Q

What is the general formula of an alcohol?

A

CnH2n+1OH

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3
Q

How do you name alcohols

A

Hydroxyl or OH

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4
Q

What kind of intermolecular forces do alcohols have? Why?

A

Hydrogen bonding, due to the electronegativity difference in the OH bond

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5
Q

How do alcohols m.p and b.p compare to other hydrocarbons of similar C chain length? Why?

A

Higher because they have hydrogen bonding—> 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 an alcohol primary?

A

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

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8
Q

What makes an alcohol secondary?

A

C bonded to OH is bonded to two other C atoms

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9
Q

What makes an alcohol tertiary?

A

C bonded to OH is bonded to three other C atoms

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10
Q

How can ethanol be made from crude oil?

A

Hydration of ethene via electrophilic addition

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11
Q

What are the advantages and disadvantages of this method?

A

Advantages- fast, continuous process, ethanol has a high purity

Disadvantage- 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 by enzymes in yeast—> ethanol

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13
Q

What conditions are needed for this reaction to take place?

A

Enzymes is yeast as catalyst 35 degree Celsius anaerobic conditions

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14
Q

Write an equation for the reaction which take place

A

C6H12O6(aq) —> 2C2H5OH + 2CO2

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15
Q

What are the 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 fractional 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 —> ethene

Not economical at the moment

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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 e.g. transport

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20
Q

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

A

Methylated spirits- methanol (toxic-can’t be drunk)

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21
Q

Write an equation for the 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 H (to form water)

24
Q

What physical conditions are needed for the elimination reaction from alcohols to alkenes? (2 alternatives)

A

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

25
Q

Draw a mechanism for the dehydration of ethanol

A

Slide 52

26
Q

Draw a method for dehydration of ethanol in the lab

A

Slide 54

27
Q

What forms if you partially oxidise a primary alcohol

A

An aldehyde

28
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

29
Q

Write an equation for the partial oxidation of ethanol

A

CH3CH2OH (l) + [O] —> CH3CHO (g) + H2O (l)

30
Q

What forms of you fully oxidise a primary alcohol

A

A carboxylic acid

31
Q

What conditions are needed for this reaction

A

Concentrated sulphuric acid, potassium dichromate (VI), reflux done for about 20 minutes, strong heating

32
Q

Write an equation for the full oxidation of ethanol

A

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

33
Q

What forms of you oxidise a secondary alcohol

A

A ketone

34
Q

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

A

A carbon-carbon bond would have to break

35
Q

What conditions are needed for the oxidation of a secondary alcohol

A

Concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating

36
Q

Write an equation for the oxidation of propan2-ol

A

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

37
Q

What is an aldehyde. What is its functional group?

A

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

38
Q

How do you name aldehydes? Give an example

A

Suffix - al

e.g. ethanal

39
Q

What is a ketone? What is its functional group?

A

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

40
Q

How do you name ketones? Give an example?

A

Suffix -one

e.g. propanone

41
Q

What is a carboxylic acid? What is its functional group?

A

Molecule with a COOH group, which has to be at the end of a carbon chain

Carboxyl functional group ( made up of carbonyl C=O and hydroxyl -OH group)

42
Q

How do you name carboxylic acids? Give an example

A

Suffix -oic acid

e.g. propanoic acid

43
Q

What does the tollens test give a positive result for

A

Aldehyde

44
Q

What is in tollens reagents?

How does this react with the substance to be tested

A

Silver nitrate in NH3 (aq) - oxidises aldehydes but not ketones

Complex silver (I) ions reduced to Ag(S)

45
Q

How do you carry out the tollens test

A

Add equal volumes of substances being tested and tollens reagent to a test tube, leave in water bath for 10mins and observe any changes

46
Q

What is the result of the tollens test for aldehydes and ketones

A

Aldehydes - silver mirror forms (solid Ag)

Ketones - no visible change

47
Q

What does Fehlings solution give a positive test result for

A

Aldehydes

48
Q

What is in Fehlings ? How does this react with the substance to be tested?

A

Blue copper (II) complex ions - gentle oxidising agent

Reduced to Cu+ ions (brick red)

49
Q

What conditions do you need to use the Fehlings solution

A

Heat

50
Q

What result do aldehydes and ketones give in the Fehlings test

A

Aldehydes - brick red ppt

Ketones - no visible change

A Level Organic Chemistry (16 decks)

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