Chapter 14 - Alcohols Flashcards

1
Q

What is the functional group of an alcohol?

A

OH

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2
Q

What does the OH group in an alcohol determine?

A

The physical and chemical properties of it

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3
Q

Why is methanol used as a fuel?

A

It combusts efficiently

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4
Q

What is methanol used for? (2)

A

Fuel

Chemical feedstock - it can be made into polymers, solvents and adhesives

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5
Q

What is ethanol used for? (3)

A

Fuel
Drinks
Solvent

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6
Q

How are alcohols named?

A

-ol is added to the prefix and the position of the OH group is indicated using a number

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7
Q

Physical properties of alcohols compared to alkanes

A

Less volatile
Higher melting points
Greater water solubility

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8
Q

Why are the physical properties of alcohols and alkanes very different?

A

Whilst alkanes are on-polar, alcohols are polar. This means that whilst there are still weak London forces present in alcohols, there are also strong hydrogen bonds

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9
Q

Why are alkanes non-polar?

A

Hydrogen and carbon have very similar electronegativities

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10
Q

What forces are present in alkanes?

A

Weak London forces

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11
Q

Why are alcohols polar?

A

The O-H bond - oxygen and hydrogen have very different electronegativities

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12
Q

Why are alcohols less volatile than alkanes?

A

The strong hydrogen bonds in alcohol molecules require much more energy to overcome in order to turn the alcohol into a gas than the weak London forces in alkanes

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13
Q

Why are alcohols soluble in water but alkanes aren’t?

A

Hydrogen bonds form between the OH group of an alcohol and the water molecule. This can’t occur in alkanes because they are non-polar

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14
Q

Why does solubility decrease as the hydrocarbon chain increases?

A

The influence of the OH group decreases

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15
Q

What are the three types of alcohols?

A

Primary, secondary, tertiary

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16
Q

What is the general formula for an alcohol?

A

Cn H2n+1 OH

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17
Q

What are primary alcohols?

A

The OH group is attached to a carbon that is attached to two hydrogens and one alkyl group

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18
Q

What is a secondary alcohol?

A

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

19
Q

What is a tertiary alcohol?

A

The OH group is attached to a carbon atom that is attached to no hydrogen atoms and three alkyl groups

20
Q

What is produced when alcohols completely combust?

A

CO2 and H2O

21
Q

What type of reaction is combustion?

A

Exothermic

22
Q

What happens to the amount of energy released when an alcohol combusts as chain length increases?

A

It increases

23
Q

How do you oxidise a primary or secondary alcohol?

A

Add an oxidising agent

24
Q

What oxidising agent do we use?

A

Potassium dichromate (K2Cr2O7) and dilute sulfuric acid (H2SO4)

25
What colour change occurs when an alcohol is oxidised?
Orange to green
26
Why does the solution go green when an alcohol is oxidised?
The dichromate (VI) ions are reduced to chromium (III) ions
27
What are the two products that can form when a primary alcohol is oxidised?
Carboxylic acids and aldehydes
28
What is produced when a primary alcohol is heated and the product distilled immediately?
An aldehyde and water
29
What is the general formula for both ketones and carboxylic acids?
CnH2nO
30
What is produced when a primary alcohol is heated under reflux?
A carboxylic acid and water
31
How to prepare an aldehyde?
Use distillation to remove the aldehyde from the reaction mixture
32
How to prepare a carboxylic acid?
Heat a primary alcohol under reflux
33
What is produced when secondary alcohols are oxidised?
Ketones and water
34
How to prepare a ketone?
Heat a secondary alcohol under reflux
35
Suffix for a ketone
-one
36
Suffix for an aldehyde
-al
37
What will happen when a tertiary alcohol is oxidised?
They can't be oxidised so the solution stays orange
38
What is dehydration of an alcohol?
When a molecule of water is removed
39
What type of reaction is dehydration?
Elimination
40
How do you dehydrate an alcohol?
Heat it under reflux in the presence of an acid catalyst - either sulfuric or phosphoric acid
41
What is produced when an alcohol is dehydrated?
An alkene and water
42
What is produced when an alcohol reacts with hydrogen halide?
A haloalkane and water
43
How to prepare a haloalkane?
Heat the alcohol under reflux with sulfuric acid and a sodium halide and a hydrogen halide is produced