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Chemistry > 15 - Alcohols > Flashcards

15 - Alcohols Flashcards

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1
Q

What is an alcohol?

A

The functional group OH attached to a hydrocarbon chain.

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2
Q

What is the general formula of an alcohol?

A

CnH2n+1OH

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3
Q

What is the suffix for alcohols?

A

ol
more than one OH group - diol, triol.

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4
Q

What is the melting/ boiling point of alcohols like?

A

High m.p and b.p compared to alkanes with a similar Mr.
Due to hydrogen bonding between molecules because of the OH group.

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5
Q

What is the solubility of alcohols like?

A

Short chain alcohols are soluble.
Long chain alcohols are insoluble.

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6
Q

Why are short chain alcohols more soluble in water?

A

Due to the ability of the OH group to hydrogen bond to water molecules.

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7
Q

Why are long chain alcohols insoluble in water?

A

Due to the non-polar hydrocarbon chain dominating over the polar OH group.

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8
Q

What is ethanol used for?

A

As an intermediate in the manufacturing of other organic chemicals.
As a solvent.

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9
Q

What are 2 ways of producing ethanol?

A

Fermentation
Hydration of ethene.

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10
Q

How does the hydration of ethene work?

Reacts and conditions

A

Ethene reacts with steam in the presence of a H3PO4 catalyst at high temperature and pressure.

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11
Q

What are the advantages of hydration of ethene?

A

Fast rate of reaction
Continuous process (efficient)
Ethanol produced is essentially pure.

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12
Q

How does fermentation work?

A

The carbohydrates from plants are broken down into glucose, which are converted into ethanol by the action of enzymes from yeast. (Anaerobic respiration).
Ethanol distilled from the mixture by fractional distillation.

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13
Q

What are the conditions of fermentation?

A

Rate affected by temperatures as low temp is too slow but high temp may denature enzymes.
Air kept out to prevent oxidation to ethanoic acid.

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14
Q

What is the formula for ethanol?

A

C2H5OH

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15
Q

What is the equation for fermentation?

A

C6H12O6(aq) –> 2C2H5OH(aq) + 2CO2(g)

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16
Q

What are the disadvantages of fermentation?

A

Slow rate of reaction
Batch process
Aqueous solution of ethanol produced.

17
Q

What are biofuels?

A

Fuels derived from renewable biological sources.

18
Q

What does carbon neutral mean?

A

When overall there is not an increase in carbon dioxide in the atmosphere.
CO2 absorbed = CO2 released.

19
Q

Why is fermentation carbon neutral?

A

Carbon dioxide released by fermentation and the combustion of ethanol = carbon dioxide absorbed by photosynthesis.

20
Q

Can alcohols be combusted?

A

Yes
Often used for fuels.

21
Q

What is methylated spirits?

A

Ethanol + little methanol

21
Q

What are the conditions for an elimination reaction/ dehydration of an alcohol?

A

Reacts with excess hot concentrated sulphuric acid.
or
Vapours passed over heated aluminium oxide.

22
Q

What is [O]?

A

An oxidising agent.

23
Q

What happens when primary alcohols are oxidised?

A

Oxidised to aldehydes then can be further oxidised to carboxylic acids.

23
Q

What is reflux?

A

When a mixture is continuously heated to boiling with the vapour condensing back into the vessel to prevent loss of substances.

24
Q

How can an aldehyde be produced from a primary alcohol?

A

The alcohol is oxidised using acidified potassium dichromate (K2Cr2O7). Distillation is used to distil the aldehyde off to prevent oxidation to carboxylic acids.
The orange dichromate is reduced to green chromium(III) ions.

25
Q

How can an carboxylic acid be produced from a aldehyde ?

A

The aldehyde is oxidised using double the amount of acidified potassium dichromate (K2Cr2O7).
The mixture is then refluxed to produce a carboxylic acid.

26
Q

What happens when secondary alcohols are oxidised?

A

Oxidised into ketones which aren’t oxidised further due to oxidation needing a C-C bond to break.

26
Q

What happens when tertiary alcohols are oxidised?

A

They are not easily oxidised as C-C bonds need to break.

27
Q

What are the two tests for aldehydes?

A

Tollens’s reagent
Fehling’s solution

28
Q

What is Tollens’s reagent test?

A

A solution of ammoniacal silver nitrate oxidises aldehydes and not ketones.
It contains silver ions which are reduced to silver when aldehydes are oxidised causing a metallic silver to form.

29
Q

What is Fehling’s reagent test?

A

Contains copper ions which will oxidise aldehydes but not ketones.
The blue solution will gradually change to a brick red precipitate of copper(I) oxide when warmed.

Chemistry (17 decks)

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