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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

Cn H2n+1 OH

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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 boning, due to the electronegative 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 hydrogen bond in water

Insoluble when long chain- non-polarity of C-H bond takes precedence

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7
Q

What make 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 making ethanol from crude oil?

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 carbo hydrates broken down and fermented by enzymes in yeast —> ethanol

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13
Q

What conditions are needed for ethanol to be formed by fermentation?

A

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

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14
Q

Write an equation for the reaction which takes place when ethanol is being formed by fermentation

A
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15
Q

What are the advantages and disadvantages of making ethanol by fermentation?

A

Advantages- renewable as from plants

Disadvantages- slow, batch process, enzymes stop working at 15% alcohol so the solution is not pure, needs 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)

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21
Q

Write an equation for the combustion of ethanol?

A
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22
Q

What is an elimination reaction?

A

The removal of a smaller molecule from a larger one

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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

Draw a mechanism for the dehydration of ethanol

A
26
Q

Draw a method for dehydration of ethanol in the lab

A
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
30
Q

What forms if you fully oxidise a primary alcohol?

A

A carboxylic acid

31
Q

What conditions are needed for a primary alcohol to be fully oxidised?

A

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

32
Q

Write an equation for the full oxidation of ethanol

A
33
Q

What forms if 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
A
36
Q
A
37
Q
A
37
Q
A
37
Q
A
38
Q
A
39
Q

How do you name aldehydes?

A

Suffix - al
e.g ethanal

40
Q

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

A
40
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=0)

41
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)

42
Q

How do you name ketones?

A

Suffix -one
e.g propanone

43
Q

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

A

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

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

44
Q
A
45
Q

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

A

Aldehydes

45
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)

46
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 mins and observe any changes

47
Q

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

A

Aldehydes- silver mirror forms
Ketones- no visible change

48
Q

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

A

aldehydes

49
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)

50
Q

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

A

Heat

51
Q

What result do aldehydes and ketone five in the Fehling’s test?

A

Aldehydes- brick red ppt
Ketones- no visible change

52
Q
A

Organic Chemistry (17 decks)

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