Alcohols Flashcards

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
What physical conditions are needed for the elimination reaction from alcohols to alkenes?
Excess hot concentrated sulphuric acid or pass | vapour over hot aluminium oxide
26
What forms if you partially | oxidise a primary alcohol?
An aldehyde
27
What conditions are needed to partially oxidise a primary alcohol?
Dilute sulphuric acid, potassium dichromate (VI), distill product as it’s produced, gentle heating
28
Write an equation for the | partial oxidation of ethanol
CH3CH2OH (l) + [O] → CH3CHO (g) + H2O (l)
29
What forms if you fully | oxidise a primary alcohol?
A carboxylic acid
30
What conditions are needed | to fully oxidise a primary alcohol?
Concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating
31
Write an equation for the full | oxidation of ethanol
CH3CH2OH (l) + 2[O] → CH3COOH (g) + H2O (l)
32
What forms if you oxidise a | secondary alcohol?
A ketone
33
Why can secondary alcohols not be oxidised further and why can’t a tertiary alcohol be oxidised?
A carbon-carbon bond would have to break
34
What conditions are needed for the oxidation of a secondary alcohol?
Concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating
35
Write an equation for the | oxidation of propan-2-ol.
CH3CH(OH)CH3 (l) + [O] → CH3COCH3 (g) + H2O (l)
36
What is an aldehyde? What is its functional group?
Molecule with C=O group at the end of a carbon chain, carbonyl functional group (C=O)
37
How do you name aldehydes? Give an example.
Suffix -al | e.g. ethanal
38
What is a ketone? What is | its functional group?
Molecule with C=O group in the middle of a carbon chain, carbonyl functional group (C=O)
39
How do you name ketones? Give an example?
Suffix -one | e.g. propanone
40
What is a carboxylic acid? | What is its functional group?
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
How do you name carboxylic acids? Give an | example
Suffix -oic acid | e.g. propanoic acid
42
What does the Tollens’ test | give a positive result for?
aldehydes
43
What is in Tollens’ reagent? How does this react with the substance to be tested?
Silver nitrate in NH3 (aq) - oxidises aldehydes but not ketones Complex silver (I) ions reduced to Ag(s)
44
How do you carry out the | Tollens’ test?
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
What is the result of the Tollen’s test for aldehydes and ketones?
Aldehydes - silver mirror forms (solid Ag) | Ketones - no visible change
46
What does Fehling’s solution give a positive test | result for?
aldehydes
47
What is in Fehling’s? How does this react with the substance to be tested?
Blue copper (II) complex ions - gentle oxidising agent Reduced to Cu+ ions (brick red)
48
What conditions do you need to use the Fehling’s solution?
Heat
49
What result do aldehydes and ketones give in the fehlings test?
Aldehydes- brick red ppt | Ketones- no visible change