Alcohols

Question 1

general formula for alcohols

Answer 1

CnH2n+1OH

Question 2

methods for making ethanol (2)

Answer 2

hydration of ethene

fermentation of sugars

Question 3

hydration of ethene

conditions, positives, negatives, how to overcone low yield

Answer 3

Conditions: 300°C, 60atm, concentrated H3PO4 catalyst

100% purity, continuous process, fast rate of reaction

Uses finite resources, high temperatures and pressures, not carbon neutral, expensive technology

Low yield but unreacted ethene is recycled

Question 4

fermentation of sugars

conditions, negatives, positives,

Answer 4

• Conditions: ~35°C , pH 7, anaerobic, enzymes from yeast
• Low purity (further distillation), batch process, slow rate of reaction, less land for crops -> famine
• Uses renewable crops, low temperatures and pressures, carbon neutral, high yield

Question 5

carbon neutral

Answer 5

an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere (photosynthesis, fermentation of glucose, combustion of ethanol balance CO2)

Question 6

biofuel

Answer 6

a fuel produced from plants

Question 7

oxidation of alcohols

Answer 7

Reagents: Acidified K2Cr2O7 and dilute H2SO4

Colour of oxidising reagent reduces from orange Cr2O72- -> green Cr3+

Question 8

Partial 1° oxidation conditions and equation

Answer 8

warm gently, distil out aldehyde

1° alcohol (OH) + [O] -> aldehyde (COH) + H2O

Question 9

Full 1° oxidation conditions and equation

Answer 9

heat under reflux with excess dichromate

1° alcohol (OH) + [O] -> aldehyde (COH) + H2O

Aldehyde (COH) + [O] -> carboxylic acid (COOH)

Question 10

Anti-bumping granules

Answer 10

prevents vigorous, uneven boiling by making small bubbles form instead of large bubbles

Question 11

2° oxidation conditions and equation

Answer 11

heat under reflux

2° alcohol (OH) -> ketone (C=O) + H2O

Question 12

why does 3° alcohol does not oxidise

Answer 12

No C-H bond attached to C of functional group

Question 13

ways to distinguish between aldehydes and ketones

Answer 13

1. Oxidise using acidified K2Cr2O7 and dilute H2SO4
2. Tollen’s reagent
3. Fehling’s reagent

Question 14

Distinguishing between aldehydes and ketones
Oxidise using acidified K2Cr2O7 and dilute H2SO4

results

Answer 14

 Aldehyde [O] into carboxylic acid

 Ketone will not [O] as there is no C-H bond attached to the C of function group

Question 15

Distinguishing between aldehydes and ketones
Tollen’s reagent

what it is, conditions, results

Answer 15

 Aqueous ammonia and silver nitrate [Ag(NH3)2]+
 Conditions: heat gently
 Aldehyde: colourless -> silver mirror formed (Ag+(aq) + e- -> Ag(s))
 Ketone: no visible change observed

Question 16

Distinguishing between aldehydes and ketones
Fehling’s reagent

what it is, conditions, results

Answer 16

 Blue Cu2+ ions
 Conditions: heat gently
 Aldehyde: brick red precipitate forms in a blue solution (Cu2+(aq) + e- -> Cu+(s)) CuSO4 -> Cu2O
 Ketone: no visible change observed

Question 17

test for carboxylic acids (3)

Answer 17

add sodium carbonate produces CO2

add sodium produces H2

add any carbonate produces CO2

Question 18

mechanism of dehydration of alcohol

equation, conditions, why its good

Answer 18

elimination
Alcohol alkene + water

Conditions: 180°C under reflux, concentrated H3PO4 catalyst/ dehydrating agent

Produce polymers from alkenes without being derived from crude oil