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Chemistry revision > Alcohols > Flashcards

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

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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4
Q

How do alcohols’ m.p. And b.p. Compare to other

hydrocarbons’ of similar C chain lengths? Why?

A

Higher, because they have hydrogen bonding → stronger than Van der Waals forces

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5
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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6
Q

What makes an alcohol primary?

A

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

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7
Q

What makes an alcohol

secondary?

A

C bonded to OH is bonded to two other C atoms

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8
Q

What makes an alcohol

tertiary?

A

C bonded to OH is bonded to three other C atoms

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9
Q

How can ethanol be made

from crude oil?

A

Hydration of ethene via electrophilic addition

phosphoric acid catalyst H₃PO₄

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10
Q

What are the advantages of ethene hydration?

A

fast, continuous process, ethanol has a high purity

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11
Q

What are the disadvantages of ethene hydration?

A

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 fermentation?

A

Enzymes in yeast as catalyst, 35°C, anaerobic

conditions

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14
Q

Write an equation for the

reaction which takes place. during fermentation

A

C6H12O6 (aq) → 2C2H5OH + 2CO2

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15
Q

What are the advantages of fermentation?

A

Renewable as from plants

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16
Q

What are the disadvantages of fermentation?

A

slow, batch process, enzymes stop working at 15% alcohol so solution is not pure, needed to be fractionally distilled

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17
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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18
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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19
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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20
Q

Why would it probably not

be entirely carbon neutral to use ethanol?

A

Other “carbon costs” associated with it e.g.

Transport

21
Q

What is a commercial fuel

that uses ethanol? What else does it contain and why?

A

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

22
Q

Write an equation for the

combustion of ethanol.

A

C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (l)

23
Q

What is an elimination reaction?

A

The removal of a smaller molecule from a larger one

24
Q

Which group leaves the
parent molecule in the case
of alcohols?

A

OH and a H (to form water)

25
Q

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

A

Excess hot concentrated sulphuric acid or pass

vapour over hot aluminium oxide

26
Q

What forms if you partially

oxidise a primary alcohol?

A

An aldehyde

27
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

28
Q

Write an equation for the

partial oxidation of ethanol

A

CH3CH2OH (l) + [O] → CH3CHO (g) + H2O (l)

29
Q

What forms if you fully

oxidise a primary alcohol?

A

A carboxylic acid

30
Q

What conditions are needed

to fully oxidise a primary alcohol?

A

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

31
Q

Write an equation for the full

oxidation of ethanol

A

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

32
Q

What forms if you oxidise a

secondary alcohol?

A

A ketone

33
Q

Why can secondary alcohols not be oxidised further and why can’t a tertiary alcohol be oxidised?

A

A carbon-carbon bond would have to break

34
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

35
Q

Write an equation for the

oxidation of propan-2-ol.

A

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

36
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)

37
Q

How do you name
aldehydes? Give an
example.

A

Suffix -al

e.g. ethanal

38
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)

39
Q

How do you name ketones? Give an example?

A

Suffix -one

e.g. propanone

40
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)

41
Q

How do you name carboxylic acids? Give an

example

A

Suffix -oic acid

e.g. propanoic acid

42
Q

What does the Tollens’ test

give a positive result for?

A

aldehydes

43
Q

What is in Tollens’ reagent?
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)

44
Q

How do you carry out the

Tollens’ test?

A

Add equal volumes of substance being tested

and tollen’s reagent to a test tube, leave in water bath for 10mins and observe any changes

45
Q

What is the result of the
Tollen’s test for aldehydes
and ketones?

A

Aldehydes - silver mirror forms (solid Ag)

Ketones - no visible change

46
Q

What does Fehling’s solution give a positive test

result for?

A

aldehydes

47
Q

What is in Fehling’s? 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)

48
Q

What conditions do you
need to use the Fehling’s
solution?

A

Heat

49
Q

What result do aldehydes
and ketones give in the
fehlings test?

A

Aldehydes- brick red ppt

Ketones- no visible change

Chemistry revision (46 decks)

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