4.2.1 Alcohols

Question 1

What is the general formula of an alcohol?

Answer 1

CnH2n+1 OH

Question 2

Describe the volatility of alcohols compared to alkanes

Answer 2

alcohols are less volatile
* as alcohols contain hydrogen bonds
* which require more energy to overcome than the induced dipole-dipole interactions in alkanes

Question 3

Describe the melting point of alcohols compared to alkanes

Answer 3

alcohols have a higher melting point
* due to hydrogen bonds

Question 4

Describe the solubility of alcohols compared to alkanes

Answer 4

alcohols are more soluble
* contain polar -OH functional group
* hydrogen bonds can form between the OH group and water molecules
* solubility decreases as the molecules get larger as there is a greater proportion of non-polar carboms

Question 5

Define primary alcohol and give examples

Answer 5

OH group is attached to the carbon atom with only one alkyl group
(methanol and ethanol - methanol is an exception as the whole thing is basically a big alkyl group)

Question 6

Define secondary alcohol and give examples

Answer 6

-OH group is attached to a carbon atom with two alkyl groups
(propan-2-ol and pentan-3-ol)

Question 7

Define tertiary alcohol and give examples

Answer 7

-OH group is attached to a carbon atom with three alkyl groups
(2-methyl-propan-2-ol and 2-methyl-butan-2-ol)

Question 8

What is the typical oxidising agent for alcohol oxidation?
What colour change will be seen?

Answer 8

potassium dichromate acidifided with dilute sulfuric acid
* orange solution containing dichromate (VI) ions will be reduced to form a green solution with chromium (III) ions

Question 9

Describe how aldehydes can be prepared from primary alcohols

Answer 9

• alcohol is gently heated with acidified potassium dichromate - forms the aldehyde
• aldehyde is distilled out of the reaction mixture as it forms to prevent any further reaction with the oxidising agent
• colour changes from orange to green

Question 10

Describe how carboxylic acids can be prepared from primary alcohols

Answer 10

• primary alcohol is heated under reflux with excess acidified potassium dichromate - carboxylic acid forms
  (using excess ensures all the alcohol is oxidised)
  (Heating under reflux ensures any aldehyde formed also undergoes oxidation into a carboxylic acid)

Question 11

Describe how Ketones are prepared from secondary alcohols

Answer 11

• alcohol is heated under reflux with the oxidising agent
• orange to green colour change
  (Ketones can not be easily oxidised so no further reactions occur)

Question 12

Do tertiary alcohols undergo oxidation reactions?

Answer 12

No - acidifided dichromate (VI) will remain orange

Question 13

What conditions are required for the dehydration of alcohols?
What are the products?

example?

Answer 13

• alcohol is heated under** reflux with an acid catalyst** (such as conc sulfuric/phosphoric acid)
• produces an alkene and molecule of water

cyclohexanol turns into cyclohexene and water

Question 14

What conditions are required for the substitution reaction of alcohols?
What are the products?

Answer 14

1. alcohol is heated under reflux with sulfuric acid and a sodium halide and the** hydrogen halide** is formed in situ (in place)
2. Hydrogen halide reacts with the alcohol to form a haloalkane