Unit 2- Organic chemistry

Question 1

Explain a primary, secondary and tertiary alcohol

2.10.1.b

Answer 1

• A primary alcohol has the functional group at the end of chain where the carbon attached to the functional group is only attached to one other carbon
• A secondary alcohol has the functional group along the chain where the carbon attached to the functional group is attached to two other carbons
• A tertiary alcohol has the functional group along the chain attached to a branch where the carbon attached to the funcational group is attached to three other carbons

Question 2

Explain the combustion of an alcohol

2.10.1.c

Answer 2

• Burns in oxygen
• Complete combustion produces carbon dioxide and water
• Forms a clean colourless flame

Question 3

Explain the reaction of an alcohol with sodium

2.10.1.c

Answer 3

• Reaction of sodium with an alcohol produces a steady steam of hydrogen gas
• Sodium does not melt
• The products formed from ethanol and sodium is sodium ethoxide and hydrogen
• Alcohol and water react similarly due to the -OH group present in water and alcohol

Question 4

Explain the reaction to form halogenoalkanes from an alcohol

2.10.1.c

Answer 4

• A substitution reaction where the -OH is replaced by the halogen
• More rapid with tertiary while least rapid with primary alcohols
• e.g. Ethanol with concentrated hydrochloric acid where the -OH is replaed by the Cl and water is formed

Question 5

Explain the reaction of an alcohol with phosphorus pentachloride

2.10.1.c

Answer 5

• Phosphorus pentachloride (PCl₅) reacts with the -OH of alcohols
• Produces hydrogen chloride gas
• Rapid reaction
• Can be used as a test to identify whether the -OH group is present
• Forms POCL₃ + HCl + the alcohol substituted with -Cl instead of -OH

Question 6

Explain the reaction of potassium dichromate (VI) with alcohols

2.10.1.c

Answer 6

• Oxidation reaction
• In a reflux condensor where the alcohol is heated
• Potassium dichromate oxidides the alcohol
• Only primary and tertiary alcohol is oxidised
• Primary alcohol forms into an aldehyde followed by a carboxylic acid
• Secondary alcohol forms into a ketone
• Potassium dichromate goes from orange to green when oxidised
• Helps to distinguish between primary, secondary and tertiary alcohols