3.3.5 Alcohols

Question 1

Alcohol hydration

Answer 1

Electrophilic addition reaction of an alkene
300˚C, 70 atm, phosphoric acid catalyst

Question 2

Fermentation of glucose conditions

Answer 2

30˚C
Yeast

Question 3

Disadvantage of fermentation of glucose

Answer 3

Ethanol produced is not pure so has to go through fractional distillation to remove impurities

Question 4

Advantages of fermentation of glucose

Answer 4

Cheap conditions
Raw materials and equipment are cheap

Question 5

Biofuel definition

Answer 5

A fuel derived from living matter, typically plants or algae, and renewable and sustainable

Question 6

Why is ethanol produced by fermentation supposedly carbon neutral

Answer 6

Photosynthesis takes in 6 CO2
6 CO2 + 6 H2O –> C6H12O6 + 6 O2
Anaerobic respiration releases 2 CO2
C6H12O6 –> 2 C2H5OH + 2 CO2
Combustion of ethanol releases 4 CO2 (for two mol of ethanol)
2 C2H5OH + 6 O2 –> 4CO2 + 6H2O
6 moles of CO2 taken in, 6 releases so carbon neutral
However doesn’t take into account transportation, irrigation of plants or fractional distillation

Question 7

Oxidation of propan-1-ol equation

Answer 7

CH3CH3CH2OH + [O] –> CH3CH3COH (propanal)

Question 8

Justify the conditions of fermentation of glucose

Answer 8

Enzymes in the yeast catalyse the reaction, converting glucose into ethanol and carbon dioxide
At lower the temperatures the reaction is too slow and at higher temperatures the enzymes are denatured

Question 9

What are primary alcohols oxidised to

Answer 9

1˚Alcohol –> Aldehyde –> Carboxylic acid

Question 10

What are secondary alcohols oxidised to

Answer 10

2˚Alcohol –> Ketone

Question 11

What are tertiary alcohols oxidised to

Answer 11

They are not easily oxidised

Question 12

What is the oxidising agent for alcohols

Answer 12

Acidified potassium dichromate

Question 13

Test to distinguish aldehydes and ketones

Answer 13

Tollens reagent - Forms a silver mirror with aldehydes, no visible change with ketones
Fehlings solution - Forms a bricked red ppt with aldehydes, no visible change with ketones
Acidified potassium dichromate - goes from orange to green for aldehydes, no colour change for ketones

Question 14

Steps of elimination of an alcohol

Answer 14

1. Alcohol is protonated by acid catalyst (phosphoric acid)
2. Positive charge on oxygen attracts electrons away from adjacent carbon
3. Water molecule is lost forming an unstable carbocation
4. Carbocation intermediate loses a proton
5. Forming an alkene

Question 15

Dehydration of alcohols conditions

Answer 15

High temperature
Phosphoric acid catalyst

Question 16

RP5 distillation of a product from a reaction method

Answer 16

1. Pour 20 cm3 of cyclohexanol into a 50 cm3 pear-shaped flask that ha been weighed. Reweigh the flask and the mass of cyclohexanol.
2. Using a plastic graduated dropping pipette, carefully add approximately 8.0 cm3 of concentrated phosphoric acid to the flask.
3. Add a few anti-bumping granules to the flask and assemble the
   semi-micro distillation apparatus, so that the contents of the flask may be distilled. Heat the flask gently, distilling over any liquid which boils below 100 °C.
4. Pour the distillate into a separating funnel and add 50 cm of saturated sodium chloride solution. Shake the mixture and allow the two layers to separate.
5. Carefully run off the lower layer into a beaker (for later disposal) and then transfer the upper layer, which contains the crude cyclohexene, into a small conical flask.
6. Add a few lumps of anhydrous calcium chloride or to the crude
   cyclohexene to remove water. Stopper the flask, shake the contents
   and allow this to stand until the liquid becomes clear.
7. Decant the liquid into a clean, dry sample container that has been
   weighed.