topic 6E

Question 1

bond angles in alcohols

Answer 1

• H-C-H bonds and C-O-C are 109.5
• H-O-C bond is 104.5

Question 2

primary, secondary & tertiary alcohols

Answer 2

• primary: 1 carbon atom attached to carbon adjoining oxygen
• secondary: 2 carbons attached to carbon adjoining oxygen
• tertiary: 3 carbons attached to carbon adjoining oxygen

Question 3

combustion of alcohols

Answer 3

CH3CH2OH + 3O2 -> 2CO2 + 3H2O

Question 4

reaction of alcohol with PCl5
- reaction formula
- observation

Answer 4

• CH3CH2OH + PCl5 -> CH3CH2Cl + POCl3 + HCl
• misty fumes of HCl produced

Question 5

reaction of alcohols to produce bromoalkane
- reagents
- equation

Answer 5

• 50% concentrated sulfuric acid and KBr
• CH3CH2OH + HBr -> CH3CH2Br + H2O

Question 6

reaction of alcohols to produce iodoalkanes
- reagent
- equation
- how is it produced

Answer 6

• phosphorus (III) iodide
• PI3 + 3CH3CH2OH -> 3CH3CH2I + H3PO3
• phosphorus (III) iodide produced in situ by reacting in red phosphorus and iodine

Question 7

why can HI not be produced by the reaction between KI and conc H2SO4

Answer 7

• the sulfuric acid will oxidise the hydrogen halides to other products

Question 8

partial oxidation reaction of primary alcohols
- reaction
- reagent
- conditions
- observation

Answer 8

• reaction: primary alcohol to aldehyde
• reagent: potassium dichromate and dilute sulfuric acid
• conditions: use a limited amount of dichromate, warm gently & distil out the aldehyde as it forms
• observation: orange dichromate ion reduced to green Cr3+ ion

Question 9

what is seen when testing for an aldehyde using Benedict’s/Fehling’s solution
- conditions
- observation

Answer 9

• conditions: heat gently
• observation: blue solutions form a red precipitate

Question 10

full oxidation reaction of primary alcohols
- reaction
- reagent
- conditions
- observation

Answer 10

• primary alcohol to carboxylic acid
• potassium dichromate solution and dilute sulfuric acid
• excess dichromate and heat under reflux
• orange to green

Question 11

oxidation reaction of secondary alcohols
- reaction
- reagent
- conditions
- observation

Answer 11

• secondary alcohol to ketone
• potassium dichromate and dilute sulfuric acid
• heat under reflux
• orange to green

Question 12

why can tertiary alcohols not be easily oxidised?

Answer 12

• carbon chain would have to be broken which requires a lot of energy

Question 13

reaction of alcohols with dehydrating agents
- reaction
- reagent
- conditions
- role of reagent
- type of reaction

Answer 13

• alcohol to alkene
• conc phosphoric acid
• warm (under reflux)
• dehydrating agent
• acid catalysed elimination