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A-Level Chemistry > Chapter 14 Alcohols > Flashcards

Chapter 14 Alcohols Flashcards

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1
Q

Alcohol homologous series

A

They all contain the -OH group (known as the hydroxyl group) which is responsible for both the physical and chemical properties of alcohols

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2
Q

Advantages of methanol

A

CH3OH - used as high-performance fuel because of its efficient combustion ; it is also an important chemical feedstock (starting material in many industrial syntheses) - can be converted into polymers, paints, solvents, adhesives and insulation

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3
Q

Where is ethanol used?

A

Alcoholic drinks and as a fuel ; homologous group increase by CH2

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4
Q

Draw 2-methylbutane-2,3-diol

A

DRAWN pg 222

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5
Q

What to keep in mind when comparing?

A

Physical properties of alcohols with alkanes with the same number of carbon atoms

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6
Q

Difference between alcohol and alkanes

A

Alcohols are less volatile and have higher melting point as well as greater water solubility than the corresponding alkanes - THESE DIFFERENCES BECOME SMALLER AS THE LENGTH OF CARBON CHAIN INCREASES

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7
Q

Why are there these differences?

A

The polarity of the bonds in both alkanes and alcohols and strength of these intermolecular forces

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8
Q

Alkanes Polarity and implications

A

Alkanes have non polar bonds because the electronegativity of hydrogen and carbon are very similar therefore alkanes molecules are non-polar THEREFORE ONLY WEAK LONDON FORCES

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9
Q

Alcohol IM and implications

A

Have a polar OH bond because of the difference in electronegativity of oxygen and hydrogen therefore they are polar and can take part in much stronger hydrogen bonds between these polar groups - weak London forces AND ALSO much stronger hydrogen bonds

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10
Q

As chain length increases

A

Contribution of OH groups decreases and therefore the alcohols resemble the alkanes more closely

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11
Q

Volatility of Alcohols/Alkenes

A

In liquid state - intermolecular hydrogen bonds hold the alcohol molecules together and thus requires a lot more energy to overcome them and turn the alcohols into gas ; more energy is required than overcoming the weak London forces in alkanes so alcohols have a lower volatility than the alkanes with the same number of carbon atoms

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12
Q

Higher the boiling point

A

Lower the volatility

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13
Q

Solubility of alcohols in water

A

Alkanes are non-polar therefore they cannot form hydrogen bonds with water. Alcohols like methanol and ethanol are completely soluble in water as hydrogen bonds form between the OH group and the water molecules. As hydrocarbon chain increases in size, influence of OH becomes smaller and solubility of longer chain becomes more like that of alkanes - solubility decrease

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14
Q

3 classifications of alcohols

A

Primary
Secondary
Tertiary

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15
Q

Primary alcohols

A

OH group is attached to a carbon atom that is attached to two hydrogen atoms and one alkyl group

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16
Q

What is methanol classified as?

A

STILL A PRIMARY EVEN THOUGH 3 HYDROGENS

17
Q

Secondary alcohol

A

The OH group is attached to a carbon atom that is attached to two alkyl groups and 1 hydrogen atom

18
Q

Tertiary alcohols

A

OH group is attached to a carbon that is attached to no hydrogen atoms and 3 alkyl groups

19
Q

Why is it important to recognise the 3 different classes of alcohol?

A

To predict how the alcohol will react with oxidising agents

20
Q

Alcohol combustion

A

Burn completely in a plentiful supply of oxygen to produce CO2 and H2O - reaction is exothermic, releasing a lot of energy in the form of heat. Number of carbon atoms in the alcohol chain increases, the quantity of heat released per mole also increases

21
Q

Usual oxidising mixture

A

Solution of potassium dichromate (VI) K2Cr2O7 acidified with dilute H2SO4

22
Q

If alcohol is oxidised then

A

Orange solution containing dichromate ions is reduced to green solution containing chromium(iii) ions

23
Q

Equation for reduction of dichromate ions

A

Cr2O7(2-) -> Cr(3+)

24
Q

Oxidation of primary alcohols

A

Oxidised to aldehydes or Cabo your acids - product of oxidation depends on reaction conditions because aldehydes oxidise themselves to COOH

25
Q

Preparation of aldehydes

A

Gentle heating of primary alcohols with acidified potassium dichromate forms an aldehyde - to ensure that the aldehyde is prepared rather than the carboxylic acid, the aldehyde is distilled out of the reaction mixture as it forms. This prevents any further reactions with the oxidising agent

26
Q

Butan-1-ol + [O]

A

Butanal + water

27
Q

Preparation of carboxylic acids

A

If a primary alcohol is heated strongly under reflux with an excess of acidified potassium dichromate (VI) - a carboxylic acid is formed. Excess ensures all the alcohol is oxidised and heating under reflux means any aldehyde initially formed also undergoes oxidation to the carboxylic acid

28
Q

Equation of oxidation of Butan-1-ol to Butanoic acid

A

But an-1-ol + 2[O] -> Butanoic acid + H2O

29
Q

How does reagent and conditions influence product formed

A

Aldehyde = distillation to remove aldehyde

Carboxylic acid = heat under reflux

30
Q

Oxidation of secondary alcohols

A

Using acidified dichromate ions - they are oxidised to Ketones - heated under reflux with oxidising mixture and colour change again from organs to green.

31
Q

Oxidation of Propan-2-ol

A

DRAW Equation

32
Q

Oxidation of tertiary

A

Do not undergo oxidation and remain orange

33
Q

Dehydration reaction

A

WATER MOLECULE IS REMOVED - alcohol heated under reflux in presence of an acid catalyst such as H2SO4/H3PO4 ; PRODUCES AN ALKENE

34
Q

What type of reaction is dehydration

A

Elimination (saturated to unsaturated)

35
Q

Equation of dehydration of cyclohexanol

A

Drawn - cyclohexene + water

36
Q

Where are atoms taken away from in dehydration

A

Adjacent carbon atoms - OH and H

37
Q

2 steps to substitution reaction of alcohols

A

1) Sodium halide + H2SO4 react to produce hydrogen halide and salt
2) hydrogen halide reacts with alcohol to produce the haloalkane - SUBSTITUTION

38
Q

Overall equation for propan-2-ol substitution

Starting with Soidum halide and acid

A

DRAWN AND TOTAL EQUATION

A-Level Chemistry (28 decks)

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