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chemistry > alcohols (organic) > Flashcards

alcohols (organic) Flashcards

1
Q

What is the functional group of an alcohol?

A

Hydroxyl group -OH

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2
Q

General formula of an alcohol

A

CnH2n+1OH

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3
Q

How do you name alcohols (1 prefix, 1 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 points 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 1 other carbon atom

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8
Q

What makes an alcohol secondary?

A

C bonded to OH is bonded to 2 other carbon atoms

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9
Q

What makes an alcohol tertiary?

A

C bonded to OH is bonded to 3 other carbon 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? (hydration)

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 fermentation to take place?

A

Enzymes in yeast as catalyst, 35’C, anaerobic conditions

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14
Q

Write an equation for fermentation?

A

C612O6(aq) > 2C2H5OH + 2CO2

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15
Q

What are 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 ethene be made? Why is it not 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 as fuel?

A

Other ‘carbon costs’ associated with it (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

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 alohols?

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 sulfuric 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 sulfuric acid, potassium dichromate (VI), distill product as its produced, gentle heating

27
Q

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 to fully oxidise a primary alcohol?

A

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

30
Q

equation for full oxidation for 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 a secondary alcohol not be oxidised further / why cant a tertiary alcohol not 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 sulfuric acid, potassium dichromate (VI), reflux for about 20 minutes, strong heating

34
Q

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 (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 group (C=O)

38
Q

How do you name ketones? Give an example

A

Suffix -one (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 (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 tollens reagent to a test tube, leave in water bath for 10 minutes and observe any changes

44
Q

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

A

Aldehydes - silver mirror forms (solid Ag)
Ketones - no visible change

45
Q

What does Fehlings solution give a positive test result for?

A

aldehydes

46
Q

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

A

Blue copper (II) complex ions - gentle oxidising agent.
Reduced Cu+ ions (brick red)

47
Q

what conditions do you need to use the Fehlings solution?

A

heat

48
Q

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

A

Aldehydes - brick red ppt
Ketones - no visible change

chemistry (34 decks)

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