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Organic Chemistry 1 > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

General formula of an alcohol?

A

C(n)H(2n+1)OH

Often shortened to ROH

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2
Q

What functional group do alcohols have?

A

—OH attached to a hydrocarbon chain

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3
Q

How is the ethanol is alcoholic drinks absorbed by the body?

A

It’s absorbed through the walls of the stomach and small intestine into the bloodstream.
Some is eliminated unchanged in urine and in breath.
The rest is broken down by the liver.

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4
Q

Describe what antifreeze is

A

Main ingredient = ethane-1,2-diol
These are added to water in the cooling systems of motor vehicles so that the resulting coolant mixture does not freeze at winter temperatures

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5
Q

How are alcohols classified?

A

Primary, secondary, or tertiary according to how many other R groups are bonded to the carbon that has the -OH group

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6
Q

Describe the physical properties of alcohols

A

The -OH group means that hydrogen bonding occurs between the molecules. So they have higher melting and boiling points than alkanes of similar RMM.

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7
Q

Describe the physical properties of alcohols (solubility)

A

The -OH group in alcohols can hydrogen bond to water molecules, but the non-polar hydrocarbon chain cannot. This means that the alcohols with short hydrocarbon chains are soluble in water because the hydrogen bonding predominates. In longer-chain alcohols the non-polar hydrocarbon chain dominates and the alcohols become insoluble in water.

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8
Q

What is the molecular formula for ethanol?

A

C2H5OH

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9
Q

Draw the mechanism for making ethanol from crude oil

A

Book (P233)

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10
Q

How is ethanol made from ethene?

A

Ethene (made from cracking crude oil) is reacted with steam, using a catalyst of phosphoric acid.
Ethene is hydrated which means that water is added across the double bond.

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11
Q

Is is ethanol made by fermentation?

A

Carbohydrates from plants are broken down into sugars and then converted into ethanol by the action of yeast.
The key step is the breakdown of sugar in a process called anaerobic respiration.

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12
Q

Can you make any alcohol (besides ethanol) using fermentation?

A

No (but you can with ethene)

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13
Q

Why does fermentation of ethanol take place in anaerobic conditions?

A

Air is kept out of the fermentation vessels to prevent oxidation of ethanol to ethanoic acid

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14
Q

State what is meant by the term biofuel

A

A fuel derived or produced from renewable biological sources

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15
Q

During fermentation of alcohols why does the process stop after the fermenting solution contains about 15% ethanol?

A

Because then the enzymes are unable to function

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16
Q

What 2 methods could be used to produce ethanol?

A

Cracking and hydration (of ethene)

Fermentation and distillation

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17
Q

Compare the rate of reaction for fermentation vs hydration.

Ethanol production

A

Fermentation is very slow; hydration of ethene is very rapid

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18
Q

Compare the type of process for fermentation vs hydration.

Ethanol production

A

Fermentation is a batch process. Everything is put into a container and then left until fermentation is complete. That batch is then cleared out and a new reaction is set up. This is inefficient.

Hydration is a continuous process. A stream of reactants is passed continuously over a catalyst. This is a more efficient way of doing things.

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19
Q

Compare the purity of what fermentation produces vs what hydration produces.
(Ethanol production)

A

Fermentation = aqueous solution of ethanol is produced

Hydration = essentially pure

20
Q

Why is ethanol made by fermentation considered carbon neutral?

A

The carbon dioxide released when it is burnt is balanced by the carbon dioxide absorbed by the plant from which it was originally obtained, during photosynthesis.

21
Q

Draw the mechanism for dehydrating ethanol to make ethene.

A

Book (P234)

22
Q

Give a renewable source of ethene

A

Ethene can be produced by dehydrating ethanol made from sugar

23
Q

At present, what is the main source of ethene?

A

Crude oil

24
Q

What is the catalyst used when making ethanol from crude oil?

A

Phosphoric acid

Catalyst used is solid silicon dioxide coated with phosphoric acid

25
Q

Is the reaction for manufacture of ethanol from ethene reversible?

A

Yes

26
Q

How can ethanol, produced by fermentation, be separated from its aqueous solution?

A

By distillation. The ethanol has a lower boiling temperature than water and would distill off first.

27
Q

Explain why fermentation and distillation can only take place as a batch process rather than continuously.

A

Fermentation takes place at a relatively low temperature and distillation at a much higher one. So the two cannot occur at the same time.

28
Q

What do complete combustion of alcohols produce? What about incomplete combustion?

A

Complete = carbon dioxide and water

Incomplete = carbon monoxide (or even carbon) and water

29
Q

In order to be dehydrated what does an alcohol need to have?

A

A hydrogen atom on a carbon next to the -OH group.

30
Q

What are elimination reactions?

A

Ones in which a small molecule leaves the parent molecules.

31
Q

In elimination reactions of alcohols, what is the molecule that always leaves the parent molecule?

A

Water.
The water is made from the -OH group and a hydrogen atom from the carbon next to the -OH group.
So the elimination reactions of alcohols are always dehydrations.

32
Q

What is formed when alcohols are dehydrated?

A

Alkene and water

33
Q

Draw the mechanism for dehydrating propan-1-ol

A

Book (P235)

34
Q

What catalysts can be used to dehydrate alcohols?

A

Hot concentrated sulphuric or phosphoric acid

35
Q

Draw and label a diagram to show how primary alcohols are oxidised.

A

Book (P236)

36
Q

What is the oxidation agent used to oxidise alcohols?

A

A solution of potassium dichromate, acidified with dilute sulphuric acid.

In the reaction, the orange dichromate ions are reduced to green chromium ions.

37
Q

Draw and label oxidation of secondary alcohols

A

Book (P236)

38
Q

Draw a distillation diagram with labels

A

Book (P237)

39
Q

Draw and label a reflux apparatus

A

Book (P237)

40
Q

What conditions are needed to oxidise primary alcohols to carboxylic acid straightaway?

A

Heat under reflux and use excess oxidising agent

Then distil

41
Q

What conditions are needed to oxidise primary alcohols to an aldehyde and stop?

A

Distil product off straight away

42
Q

What do aldehydes and ketones have in common?

A

Both have carbonyl groups (C=O group)

43
Q

What is the difference between aldehydes and ketones?

A

Aldehyde - the carbonyl group is at the end of the hydrocarbon chain)

Ketone - the carbonyl group is in the body of the hydrocarbon chain

44
Q

Name 2 tests that could be used to distinguish between aldehydes and ketones (+ why it works)

A

The Tollens’ (silver mirror) test or the Fehling’s test

  • Both tests involve gentle oxidation
  • Aldehydes are oxidised to carboxylic acid
  • Ketones are not changed by gentle oxidation
45
Q

Describe the Tollens’ (silver mirror) test

A

Tollens’ reagent is a gentle oxidising agent. It is a solution of silver nitrate in aqueous ammonia. It contains colourless silver complex ions, containing Ag+, which are reduced to metallic silver, Ag, as the aldehyde is oxidised.

It oxidises aldehydes but has no affect on ketones.

On warming an aldehyde with Tollens’ reagent, a deposit of metallic silver is formed on the inside of the test tube - the silver mirror.

46
Q

Describe the Fehling’s test

A

The Fehling’s reagent contains blue copper complex ions which will oxidise aldehydes but not ketones.

During oxidation, the blue solution gradually changes to brick red precipitate of copper oxide.

On warming with an aldehyde with blue Fehling’s solution a brick red precipitate gradually forms.

Organic Chemistry 1 (7 decks)

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