Chemistry Extended Response 2

Question 1

How much percent of the world’s ethanol is produced by fermentation synthesis?

Answer 1

~93%

Question 2

How long does synthesising by fermentation take?

Answer 2

~2 to 3 days

Question 3

What has been the longest use of synthesis by fermentation?

Answer 3

Used for alcoholic beverage production for thousands of years.

Question 4

Why is cooling required in synthesis by fermentation?

Answer 4

Because it is an exothermic reaction and so it ie required because excessive heating denatures the enzymes

Question 5

What produces enzymes and what do they do?

Answer 5

Yeast produces enzymes capable of catalysing the conversion of plant carbohydrates such as starch or sugar into ethanol.

Question 6

What sort of agricultural products are used to produce ethanol?

Answer 6

Corn, wheat, or sugar cane

Question 7

What are the two major chemical reactions that produce ethanol by fermentation?

Answer 7

1. Hydrolysis of sucrose to glucose and fructose (isomers of C6H12O6). The reaction is catalysed by the yeast enzyme invertase or sucrase.
2. Fermentation of the glucose/fructose to ethanol and carbon dioxide. Catalysed by the yeast enzyme zymase.

Question 8

What are molasses

Answer 8

Waste products of sugar refining

Question 9

What is required if molasses are used as yeast for fermentation?

Answer 9

Dilution is required to produce a 10-15% sucrose solution

Question 10

What temperature and pH is normally used for synthesis by fermentation

Answer 10

A temperature of 25 - 37 degrees is used with a pH range of 3-5 to kill bacteria and favour yeast growth.

Question 11

What is an advantage of hydration of ethene rather than fermentation

Answer 11

It is quicker.

Question 12

What is one use of hydration of ethene?

Answer 12

They are used as a feedstock for the manufacture of industrial chemicals.

Question 13

Describe the process of hydration of ethene.

Answer 13

Uses acid catalysed addition of water to ethene and is easily adapted as a continuous process.

Involves passing a mixture of steam and ethene through a catalyst bed made of silica particles coated with pure phosphoric acid as the catalyst.

Question 14

What temperature and pressure are used for the hydration of ethene?

Answer 14

• Temperature of ~300deg and pressure of 6-7 MPa (60-70 atm) is used.

Question 15

Is the hydration of ethene exothermic or endothermic?

Answer 15

The reaction is exothermic and so products are favoured.

Question 16

What is usually done to maximise the rate of reaction and yield in the hydration of ethene?

Answer 16

A compromise between maximising rate (high temp) and maximising yield (low temp) is used. High pressure favours both high yield and fast rate while the use of a catalyst H3PO4 increases rate while having no effect on yield.

Question 17

What is the ethene-to-water ratio?

Answer 17

1:0.6

Question 18

What is the initial concentration of ethanol produced and how is it maximised?

Answer 18

A conversion to ethanol of 5% occurs as the reagents quickly pass through the catalyst bed
Then the ethanol is separated from the mixture and continually recycling the unreacted ethene and steam creates an overall yield of 95%.

Question 19

What are the 3 issues with the hydration of the ethene process?

Answer 19

o Does not have environmental advantages such as bioethanol
o Produced from non-renewable resources
o Contributes to increasing atmospheric CO2.

Question 20

Why would the ethanol mixture be distilled with water?

Answer 20

The resulting ethanol can be distilled to separate any water or other impurities.

Question 21

Draw 3 comparisons between the hydration of ethene and fermentation of yeast processes

Answer 21

Synthesis by Fermentation
- Uses a biofuel manufactured using biomass
- Conducted at Atmos. Pressure and uses temp of 25-35deg and moderate pH
- Uses renewable resources (biomass)

Hydration of Ethene
- Uses non-renewable resources (fossil fuels)
- Uses pressures 60-70x greater than atmos. pressure and corrosive acid catalyst (e.g.H3PO4)
- Originates from fossil fuels

Question 22

How do enzymes react to changes in temperature and pH?

Answer 22

Enzymes are sensitive to both temperature and pH, can be denatured by high temperatures and unsuitable pH.

Question 23

Describe how the respiratory process of yeast enables it to produce ethanol.

Answer 23

Initially the yeast respires aerobically and reproduces quickly and deplete the available oxygen. By removing air from the fermentation vat the mixture soon becomes anaerobic (no oxygen). This forces yeast to respire anaerobically by converting glucose to ethanol rather than to water and carbon dioxide (aerobic respiration).

Question 24

What do nutrients do for the yeast in the fermentation process?

Answer 24

Nutrients are added to promote the initial growth and reproduction of the yeast. E.g. diammonium hydrogenphosphate (NH4)2HPO4.

Question 25

What occurs at a ethanol concentration of 8-14% in the fermentation process?

Answer 25

At an ethanol concentration of 8-14% fermentation ceases because the yeast have been poisoned by their produced ethanol.

Question 26

How is the yield of ethanol maximised in the fermentation process?

Answer 26

Yeast is separated from the fermentation mixture and distillation is used to raise the alcohol concentration to 95% (by mass).

Question 27

What occurs at an ethanol separation beyond 95.6%?

Answer 27

Ethanol separation beyond 95.6 causes the formation of an azeotrope a mixture with a constant composition and boiling temperature.

Question 28

List the steps that are taken to produce ethanol via fermentation from starch products. What are some examples of these products?

Answer 28

Ethanol can also be produced from the fermentation of starch products like wheat or corn:
1.Starch is mixed with water and adjusted to pH ~ 6

2.In the presence of alpha amylase, the mixture is heated ~ 90deg breaking it down to simple sugars.

3.The mixture is then cooled to about 33deg.

4.Glucoamylase enzyme and a yeast is added. The enzyme further breaks down the sugars to glucose and other simple sugars which are then fermented as normal.