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A-Level Chemistry > 14 Alcohols > Flashcards

14 Alcohols Flashcards

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1
Q

What functional group do all alcohols contain?

A

-OH (hydroxyl group)

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2
Q

What is the functional group responsible for?

A

Physical and chemical properties of the alcohol

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3
Q

How do you name an alcohol?

A

Suffix -ol added to the stem name of the longest carbon chain
Position of -OH indicated

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4
Q

State the different in physical properties of the alcohols with alkanes (with the same number of carbon atoms)

A

Alcohols are:
Less volatile
Higher melting points
Greater water solubility

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5
Q

What happens to the difference in physical properties as the length of the carbon chain increases?

A

Become smaller

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6
Q

Define volatile

A

How readily something turns into a gas

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7
Q

Why do alcohols have higher melting points and are less volatile?

A

-Weak London forces
- Hydrogen bonds (strongest intermolecular bond relatively large amount of energy required to break)

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8
Q

Describe the polarity and intermolecular forces in alcohols

A

Polar O-H because of electronegativity difference so alcohol molecules are polar
Hence, also have stronger hydrogen bonds between the O-H groups

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9
Q

Why are alcohols soluble in water?

A

Hydrogen bonds form between the polar -OH group and the water molecules

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10
Q

Explain what happens to the solubility of alcohols as the chain increases

A

As the alkyl chain gets longer, the influence of the -OH group on the properties becomes less important
So bigger alcohols are more like corresponding alkane (solubility decreases)

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11
Q

What are the 3 classifications of alcohols?

A

Primary, secondary and tertiary

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12
Q

How do you classify alcohols as primary, secondary or tertiary?

A

Primary: carbon bonded to the -OH is bonded to 1 alkyl group and 2 hydrogens
Secondary: carbon bonded to the -OH is bonded to 2 alkyl group and 1 hydrogens
Tertiary: carbon bonded to the -OH group is bonded to 3 alkyl groups

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13
Q

What are the 4 reactions of alcohols?

A

Combustion
Oxidation (not adding oxygen!)
Dehydration
Substitution

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14
Q

Describe the combustion of alcohols and write a chemical equation for ethanol

A

Useful fuels
Burned in a plentiful supply of oxygen, energy released
C2H5OH +3O2 –> 2CO2 + 3H2O

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15
Q

What happens to the energy released in a combustion reaction as the chain increases?

A

As the number of carbon atoms in the chain gets bigger, the amount of energy released per mole also increases

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16
Q

What is the colour change if an alcohol is oxidised?

A

Orange to green

17
Q

What is the oxidising agent for the oxidation of alcohols?

A

Potassium dichromate (VI) in sulphuric acid

18
Q

What do primary alcohols oxidised on gentle heating and distillation?

A

Aldehyde

19
Q

Give the displayed formula for the gentle heating of ethanol with potassium dichromate (VI) with sulphuric acid

A

OH H O
| | ||
CH3–C—H + [O] –> H–C–C—-H +H2O
| |
H H

Ethanol –> Ethanal

20
Q

What do primary alcohol oxidise to under reflux and excess acidified potassium dichromate?

A

Carboxylic acid

21
Q

Draw an equation for the oxidation of propanol-1-ol under reflux

A

CH3CH2CH2(OH) +2[O] –> CH3CH2COOH + H2O

Propanoic acid

22
Q

Why does there need to be excess acidified potassium dichromate (VI) and reflux?

A

Excess ensures that all the alcohol reacts
Heating under reflux ensures that the aldehyde undergoes further oxidation all the way to the carboxylic acid

23
Q

What do secondary alcohols oxidise and under what conditions?

A

Ketones
Reflux - guarantee reaction is finished
Not possible to oxidise ketones any further

24
Q

Draw an equation for the oxidation of propan-2-ol

A

CH3CH(OH)CH3 + [O] –> CH3COCH3 +H2O

25
Q

What do tertiary alcohols oxidise to and why?

A

Do not undergo oxidation!!!
Would require breaking of a C-C bond

26
Q

What is dehydration of alcohols?

A

Involves losing a molecule of water to form an alkene

27
Q

What are the conditions for dehydration?

A

Concentrated phosphoric acid as a catalyst

28
Q

Draw an equation for the dehydration of propan-1-ol

A

CH3CH2CH2(OH) –> CH3CH2CH2 + H2O
Propan-1-ol –> propene and water

29
Q

What type of reaction is a dehydration?

A

Elimination (opposite of an addition reaction)

30
Q

What are the 2 reactions for a substitution reaction?

A

Heated under reflux with sulfuric acid and sodium bromide, generating the HBr in situ (NaBr + H2SO4 –> NaHSO4 + HBr)
Then:
CH3CH2CH2(OH) +HBR –> CH3CH2CH2BR +H2O

A-Level Chemistry (15 decks)

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