Alcohols

Question 1

what is an alcohol

Answer 1

an organic molecule containing an -OH functional group

Question 2

molecular and display formula for ethanol

Answer 2

Question 3

what would you name this molecule

Answer 3

propan-2-ol

Question 4

structural formula of ethanol

Answer 4

Question 5

what are the two methods of making ethanol and what is the main reason for choosing one

Answer 5

• hydration of ethene
• fermentation of glucose

which method gets used depends mostly on the availability of crude oil or sugar cane in different parts of the world

Question 6

what is the raw material used in the hydration of ethene

Answer 6

crude oil (provides the ethene)

Question 7

advantages of the hydration of ethene method for creating ethanol

Answer 7

• makes pure ethanol (and therefore produces no waste products)
• can run continuously
• fast rate of reaction

Question 8

disadvantages of the hydration of ethene method for creating ethanol

Answer 8

• conditions require a lot of energy
• non-renewable raw material used

Question 9

how to perform the hydration of ethene method for creating ethanol

Answer 9

Ethene is made when alkanes undergo cracking, then ethene gas is mixed with steam under the following conditions:

300*C
65 atm pressure
phosphoric acid catalyst

Question 10

what raw material is used in the fermentation of glucose

Answer 10

sugar cane

Question 11

disadvantages of the fermentation method for creating ethanol

Answer 11

• makes impure ethanol
• must be done in individual batches
• slow process (20-60hours)
• CO2 gas is released

Question 12

advantages of the fermentation method for creating ethanol

Answer 12

• renewable raw material used
• conditions do not require a lot of energy

Question 13

how is the fermentation method for creating ethanol carried out

Answer 13

glucose is fermented microbiologically under the conditions:

• yeast present (provides enzymes)
• 30*C (enzymes optimum temperature)
• anaerobic (prevents oxidation)

Question 14

during the fermentation of glucose what would happen if there was no bung or air trap

Answer 14

the ethanol will be oxidised and form ethanoic acid

Question 15

during the fermentation of glucose why do we use an air trap instead of a solid bung

Answer 15

it lets gas out but not in - avoids the co2 building up and causing an explosion

Question 16

what do you have to do to the product of the fermentation of glucose

Answer 16

fractional distillation - to separate the ethanol and the water.

water has a higher boiling point than ethanol so as they both rise up the column it cools and condenses and fall back down while the ethanol reaches the top of the fractionating column and enters the condenser

Question 17

what are the three ways that ethanol can be oxidised

Answer 17

• combustion
• microbial oxidation
• chemical oxidation

Question 18

how does microbial oxidation work

Answer 18

microorganisms such as bacteria and fungi can use the oxygen in the air to oxidise ethanol into ethanoic acid

Question 19

how does chemical oxidation occur and how can we observe it

Answer 19

When we want to deliberately oxidise ethanol in the lab, we heat it with a mixture of:
* Potassium dichromate
* Dilute sulfuric acid

the reaction is always accompanied by the same colour change because the orange dichromate ions are turned into green chromium ions.