4.4 ALCOHOLS

Question 1

What is a primary alcohol?

Answer 1

A primary alcohol is where the OH group is attached to a carbon that is bonded to 2 hydrogens and 1 alkyl group.

Question 2

What is a secondary alcohol?

Answer 2

A secondary alcohol is where the OH group is attached to a carbon that is bonded to 1 hydrogen and 2 alkyl groups.

Question 3

What is a tertiary alcohol?

Answer 3

A tertiary alcohol is where the OH group is attached to a carbon that is bonded to 3 alkyl groups.

Question 4

What are the products of combustion with alcohols?

Answer 4

During complete combustion with alcohols, CO2 and H2O are formed.
During incomplete combustion with alcohols, CO/C and H2O are formed.

Question 5

What is dehydration of alcohols?

Answer 5

Dehydration of alcohols is the elimination of water.
- forms alkenes
- alcohol heated under reflux in the presence of a catalyst (usually concentrated sulfuric acid or phosphoric acid)
- produces an alkene and water

Question 6

What is the substitution of alcohols?

Answer 6

Substitution reaction of alcohols:
-alcohols react with hydrogen halides to form haloalkanes
step 1-
- alcohol is heated under reflux with sulfuric acid and a sodium halide
step 2-
- this forms the hydrogen halide which then reacts with the alcohol to form a haloalkane (OH replaced with halogen atom)

e.g 1. NaBr + H2SO4 = NaHSO4 + HBr
2. C3H7OH + HBr = C3H7Br + H2O

Question 7

What colour do primary, secondary and tertiary alcohols turn when oxidised with dichromate?

Answer 7

Oxidation of alcohols (colour change):
primary - orange to green
secondary - orange to green
tertiary - stays orange

Question 8

What is formed when primary alcohols are oxidised?

Answer 8

The oxidation of primary alcohols is a two step reaction, and can form aldehydes and carboxylic acids and water. To oxidise into an alcohol, distillation is used with excess alcohol, to oxidise into a carboxylic acid, the alcohol is heated under reflux with excess acidified potassium dichromate.

Question 9

What is formed when secondary alcohols are oxidised?

Answer 9

Secondary alcohols can be heated under reflux to form ketones and water, but cannot be further oxidised.

Question 10

What is formed when tertiary alcohols are oxidised?

Answer 10

Tertiary alcohols are resistant to oxidation, so no reaction takes place, as carbon can only make 4 bonds and there is no space for another atom.