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A-Level Chemistry > 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

Cn H2n+1 OH

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3
Q

How do you name alcohols (one prefix, one suffix)?

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’ melting point and boiling point 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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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 (phosphoric acid catalyst H₃PO₄)

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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.

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 by enzymes 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, 35°C, anaerobic conditions.

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14
Q

Write an equation for the reaction which takes 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 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 → 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, so it can’t be drunk).

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 a 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

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

Write an equation for the partial oxidation of ethanol

A

CH3CH2OH (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 for about 20 mins, strong heating.

30
Q

Write an equation for the full oxidation of ethanol

A

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

31
Q

What forms if you oxidise a secondary alcohol?

A

A ketone

32
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

33
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.

34
Q

Write an equation for the oxidation of propan-2-ol.

A

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

35
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)

36
Q

How do you name aldehydes? Give an example.

A

Suffix -al
e.g. ethanal

37
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).

38
Q

How do you name ketones? Give an example?

A

Suffix -one
e.g. propanone

39
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).

40
Q

How do you name carboxylic acids? Give an example

A

Suffix -oic acid
e.g. propanoic acid

41
Q

What does the Tollens’ test give a positive result for?

A

aldehydes

42
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)

43
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.

44
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.

45
Q

What does Fehling’s solution give a positive test result for?

A

aldehydes

46
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).

47
Q

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

A

Heat

48
Q

What result do aldehydes and ketones give in the Fehling’s test?

A

Aldehydes- brick red ppt.

Ketones- no visible change

A-Level Chemistry (16 decks)

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