3.3.5 Alcohols

Question 1

What is the suffix and prefix used when naming alcohol?

Answer 1

-ol, hydroxyl-

Question 2

What are the two different methods for producing ethanol?

Answer 2

Fermentation, direct hydration.

Question 3

How does fermentation produce ethanol, under what conditions?

Answer 3

Produced by using living yeast to convert glucose sugars into ethanol and CO2. Atmospheric pressure, 35-37C, anaerobic.

Question 4

Why does fermentation need to happen under anaerobic conditions?

Answer 4

Prevents oxidation of ethanol to ethanoic acid.

Question 5

What is the equation for fermentation?

Answer 5

C6H12O6 —–(yeast)—-> 2C2H5OH + 2CO2

Question 6

How does direct hydration produce ethanol, under what conditions?

Answer 6

Ethene reacts with steam, at 300C, at pressure of 6.5 x 10^3 KPa and with phosphoric acid as a catalyst.

Question 7

What is the equation for direct hydration?

Answer 7

CH2=CH2 + H2O(g) —-phosphoric acid catalyst—> C2H5OH

Question 8

What happens in the mechanism for the reaction from direct hydration?

Answer 8

The = breaks to give the e- to the H+ ion (from the acid), this forms C2H5 with a carbocation and the O from the H2O donates an e- to the carbocation, the C2H5 then bonds to the H2O making O a + ion as it has too many bonds. One of the Hs from the H2O donates an electron to the O forming C2H5OH and a H+ (proton).

Question 9

Explain why the phosphoric acid catalyst isn’t used up in direct hydration.

Answer 9

Because the H+ ions are used up at the start of the reaction and then given back out at the end.

Question 10

What are the speeds of the methods to form ethanol?

Answer 10

Hydration is fast, fermentation is slow.

Question 11

What are the purities of the methods to form ethanol?

Answer 11

Hydration is pure (around 100%), fermentation is impure (max. 20%).

Question 12

What are the raw materials used in the methods to form ethanol, which are renewable?

Answer 12

Hydration uses ethene from crude oil (non-renewable), fermentation uses sugars/biomass (renewable).

Question 13

What are the types of processes used in the methods to form ethanol?

Answer 13

Hydration is continuous, fermentation is batch.

Question 14

What are the costs for the methods to form ethanol?

Answer 14

Hydration is cheap on manpower, expensive on equipment. Fermentation is expensive on manpower, cheap on equipment.

Question 15

What are alcohols classified as?

Answer 15

Primary, secondary or tertiary.

Question 16

What is the oxidising agent used to oxidise alcohols? What is it usually represented as?

Answer 16

Acidified potassium dichromate (VI) solution/ acidified K2Cr2O7.
Usually represented as [O].

Question 17

What can primary alcohols be oxidised to? What are the conditions?

Answer 17

Aldehydes. Room temp, ethanal must be removed by distillation to prevent further oxidation.

Question 18

What is the equation for oxidising an alcohol to an aldehyde?

Answer 18

. H H H
| | [O] |
H - C - C - OH ——> H - C - C = O + H2O
| | | |
H H H H

CH3CH2OH(l) + [O] -> CH3CHO(l) + H2O(l)

Question 19

What can primary alcohols be oxidised further into? What are the conditions?

Answer 19

Carboxylic acids. Higher temperature, must be refluxed.

Question 20

What is the equation for the oxidation of a primary alcohol into a carboxylic acid?

Answer 20

. H H H
| | 2[O] |
H - C - C - OH ——> H - C - C = O + H2O
| | | |
H H H OH

CH3CH2OH(l) + 2[O] -> CH3COOH(l) + H2O(l)

Question 21

What are secondary alcohols oxidised to?

Answer 21

Ketones.

Question 22

What is the equation for oxidising a secondary alcohol into a ketone?

Answer 22

. H H H H H H
| | | [O] | | |
H - C - C - C - H ——> H - C - C - C - H + H2O
| | | | || |
H OH H H O H

CH3CH(OH)CH3(l) + [O] -> CH3COCH3(l) + H2O(l)

Question 23

What do we oxidise tertiary alcohols into?

Answer 23

Nope. Can’t oxidise because oxidation means a C-C bond has to be broken, needs lots of energy, no H atoms available for oxidation.

Question 24

What are the 3 chemical tests used to distinguish between aldehydes and ketones?

Answer 24

Acidified potassium dichromate (VI), Tollen’s reagent, Fehling’s solution.

Question 25

What are the results for the potassium dichromate test?

Answer 25

Aldehyde colour change = orange to green solution

Ketone = no change.

Question 26

What are the results for the Tollen’s reagent?

Answer 26

Only reacts with aldehydes, silver atoms coat the test tube to make a silver mirror.

Question 27

What are the results for the Fehling’s solution test?

Answer 27

Only reacts with aldehydes, produces a brick red precipitate on warming.

Question 28

What do elimination reactions involve?

Answer 28

The loss of water from a molecule.

Question 29

What is an elimination reaction often called?

Answer 29

Dehydration.

Question 30

What are the conditions for acid catalysed elimination?

Answer 30

Heated (180C) with H2SO4 or H3PO4. OR vapours heated (600K) over aluminum oxide catalyst.

Question 31

What is produced from acid catalysed elimination? How is it collected?

Answer 31

Ethene product is collected over water.

Question 32

Why is ethene useful?

Answer 32

It’s the starting point for plastic manufacturing (making polymers).

Question 33

What is the mechanism for an elimination reaction?

Answer 33

Curly arrow starts from lone pair on the O of the alcohol and goes to a proton (H+). Next step, arrow starts from C-H bond and goes to C-C bond, other arrow goes from C-O bond to the O+. Last step, alkene formed along with H2O and H+.

Question 34

What could acid catalysed elimination be used to replace?

Answer 34

Replace making polymers from crude oil, ethanol from plants could be used to make the alkane monomers.