Chapter 14: Alcohols

Question 1

What is the functional group of an alcohol?

Answer 1

• The hydroxyl group

- OH

Question 2

What is the simplest alcohol?

What is it used for?

Answer 2

Methanol

• It is used as a high performance fuel because of its efficient combustion

Question 3

What are other important uses of methanol?

Answer 3

• It is an important chemical feedstock
• The starting material in many industrial synthesis
• It can be converted into polymers, paints solvents, insulation, adhesives and many other useful products

Question 4

State some properties of alcohols (compared to alkanes)

Answer 4

• Less volatile
• Have higher boiling points
• Greater solubility

Question 5

Explain the properties of alcohols (and alkanes)

Answer 5

• The alkanes have non-polar bonds because the electro-negativity of hydrogen and carbon are very similar
• The alkane molecules are therefore non-polar
• The intermolecular forces between non-polar molecules are very weak non-polar London forces
• Alcohols have a polar O-H bond because of the difference in electro-negativity of the oxygen between the oxygen and hydrogen atoms
• Alcohol molecules are therefore polar
• The intermolecular forces will be very weak London forces but there will also be much stronger hydrogen bond between the polar O-H

Question 6

Volatility and boiling points (alkanes vs alcohols)

Answer 6

• Intermolecular hydrogen bonds hold the alcohol molecules together
• These bonds must be broken in order to change the liquid alcohol into a gas
• This requires more energy than overcoming the weaker London forces in alkanes so alcohols have a lower volatility than alkanes of the same number of carbon atoms

Question 7

Solubility in water (Alkanes vs alcohols)

Answer 7

• Alkanes are non-polar molecules and cannot form hydrogen bonds with water
• Alcohols are completely soluble in water, as hydrogen bonds form between the polar -OH group of the alcohol and the water molecules

Question 8

What happens as the hydrocarbon chain increases in size

Answer 8

-The influence of the -OH group becomes relatively smaller, and the solubility of the longer-chain alcohols becomes more like that of hydrocarbons-solubility decreases

Question 9

How are alcohols classified?

Answer 9

• Depends on the number of hydrogen atoms and alkyl groups attached to the carbon atom that contains the alcohol functions group

Question 10

What are primary alcohols?

Answer 10

• The OH group is attached to a carbon atom that is attached to one alkyl group

Question 11

What are secondary alcohols?

Answer 11

• The OH group is attached to a carbon atom that is attached to two alkyl groups

Question 12

What are tertiary alcohols?

Answer 12

• The OH group is attached to a carbon atom that is attached to three alkyl groups

Question 13

What do alcohols burn in a plentiful supply of oxygen to produce?

Answer 13

• carbon dioxide and water

Question 14

What kind of reaction is the combustion of alcohols?

Answer 14

• Exothermic

- It releases a large quantity of energy in the form of heat

Question 15

Name an oxidising agent

Answer 15

• Potassium dichromate

Question 16

What will be observed if the alcohol is oxidised using potassium dichromate?

Answer 16

A colour change from orange to green

Question 17

What can primary alcohols be oxidised to?

Answer 17

Alcohols or carboxylic acids

Question 18

Preparation of aldehydes:

Answer 18

On gentle heating of primary alcohols with acidified potassium dichromate, an aldehyde is formed

Question 19

How do you ensure that a aldehyde is produced instead of a carboxylic acid?

Answer 19

• The aldehyde is distilled out of the reaction mixture as it forms
• This prevents any further reaction with the oxidising agent

Question 20

Preparation of carboxylic acids?

Answer 20

• If a primary alcohol is heated strongly under reflux, with an excess of acidified potassium dichromate, a carboxylic acid is formed

Question 21

How can you ensure that all of the alcohol is oxidised?

Answer 21

• Use of an excess of acidified potassium dichromate

Question 22

What does heating under reflux ensure?

Answer 22

• It ensures that any aldehyde formed initially in the reaction also undergoes oxidation to carboxylic acid

Question 23

What does oxidation of a secondary alcohol produce?

Answer 23

A Keytone

Question 24

What can be done to ensure that oxidation of secondary alcohol goes to completion?

Answer 24

It is heated under reflux with the oxidising agent

Question 25

What is produced during the oxidation of tertiary alcohols?

Answer 25

Tertiary alcohols do not undergo oxidation reactions

-The acidified dichromate remains orange when added to a tertiary alcohol

Question 26

What is dehydration?

Answer 26

-Any reaction in which a water molecule is removed from the starting material

Question 27

How can an alkene be produced from an alcohol?

Answer 27

• Heat the alcohol under reflux

- In the presence of an acid catalyst such as concentrated sulfuric acid or phosphoric acid

Question 28

Dehydration of an alcohol is an example of what kind of reaction?

Answer 28

An elimination reaction

Question 29

How can a haloalkane be produced from an alcohol?

Answer 29

• The alcohol is heated under reflux with sulfuric acid and a sodium halide
• It is formed in situ