Green Chemistry

Question 1

What are the 12 principles of green chemistry? 
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Answer 1

• prevent waste
• design less hazardous chemical syntheses
• Use renewable raw materials (Use renewable feedstocks)
• use catalysts, not excess reactants
• avoid chemical derivatives
• Maximise atom economy
• design safer chemicals and products
• use safer solvents and reaction conditions
• increase energy efficiency
• design chemicals and products that are biodegradable
• analyse in real time to prevent pollution
• minimise the potential for accidents

Question 2

Describe the principle of preventing waste

Answer 2

Design chemical processes to prevent waste rather than treat waste or clean it up after it is formed
- eg. Taking CO2 from other process that produce it to expand the polystyrene and so less CO2 is produced in the environment

Question 3

Describe the principle of design less hazardous chemical syntheses

Answer 3

design less hazardous chemical syntheses

Design safer methods that use and generate substances with little or no toxicity to humans and the environment.

Question 4

Describe the principle of Use renewable raw materials (Use renewable feedstocks)

Answer 4

Use renewable raw materials (Use renewable feedstocks)
Use starting materials that are derived from renewable resources, such as plant materials, rather than form finite resources, such as fossil fuels
eg. instead of using crude oil for ink, soy based ink is used instead for recycling paper.

Question 5

Describe the principle of use catalysts, not excess reactants

Answer 5

Minimise waste by using small amounts of catalysts that can carry out a single reaction many times. Using a catalyst is preferable to using excess reactants, which creates waste.
Biocatalysts
enzymes or whole-cell microorganisms

Question 6

Describe the principle of avoid chemical derivatives

Answer 6

When a chemical has to be produced from another chemical before it can be used, additional reagents are used and extra waste is generated.
time and energy and waste
Chemoselecting: only at a particular functional groups

Question 7

Describe the principle of Maximise atom economy

Answer 7

Design syntheses so that the final product contains the maximum proportion of the starting materials. There should be few, if any, wasted atoms
how efficiently a reaction occurs.
%Atom Economy= (FW of atoms ulilised/FW of all reactants) x100

Question 8

Describe the principle of design safer chemicals and products

Answer 8

Design chemical products to be fully effective, yet to have little or no toxicity

Question 9

What is the energy use of ethanol by fermentation?

Answer 9

conducted at room pressure and ambient temperature (~37C) so less energy is required to heat reagents or create high pressures

Question 10

What is the energy use of ethanol by addition?

Answer 10

Considered energy is needed to heat reagents (~300C) and raise pressure (60-70 atm) in order to achieve a satisfactory reaction rate and yield.

Question 11

What does ethanol by fermentation use to produced ethanol?

Answer 11

renewable biomass and biomass waste products

Question 12

What does ethanol by addition use to produced ethanol?

Answer 12

non-renewable fossil fuel based products

Question 13

Is the produce or use of toxic substances used in the production of ethanol by fermentation?

Answer 13

Neither sugar nor yeast are toxic reagents. While product CO2 occurs naturally in the environment. High concentrations of CO2 are asphyxiating in confined spaces

Question 14

Is the produce or use of toxic substances used in the production of ethanol by addition?

Answer 14

Ethene is a highly flammable hazardous gas. It is an asphyxiant (due to oxygen exclusion). The acid catalyst, pure phosphoric acid, is a corrosive and hazardous substance.

Question 15

Is safety violated during the production method of ethanol by fermentation?

Answer 15

Fermentation occurs in enclosed vats at ambient temperature and pressure and may be considered to pose few safety risk.

Question 16

Is safety violated during the production method of ethanol by addition?

Answer 16

Involves the use of high temperatures and pressures as well as the flammable gas ethene and the corrosive acid catalyst H3PO4. These reagents and conditions pose inherent safety risks.

Question 17

How is atom economy of ethanol by fermentation?

Answer 17

Fermentation has a low atom economy as a considerable amount of the reactant mass ends up as waste, ie. CO2

Question 18

How is atom economy of ethanol by addition?

Answer 18

Has 100% atom economy as all reactant atoms are incorporated into ethanol, ie there is no other product

Question 19

How is biodiesel obtained from the final reaction mixture and what further treatment of the biodiesel may be required? (2 steps)

Answer 19

biodiesel and glycerol are insoluble in one another therefore it forms two separate layers. Biodiesel is separated from the top layer while denser glycerol from a bottom layer. Most excess methanol (or other alcohol), base catalyst and any soap that may have formed remain in the glycerol layer with smaller amounts in the biodiesel.

Biodiesel is then washed with warm water to remove any residual methanol, catalyst, glycerol or soap it may contain. Impurities are very soluble in water while water is insoluble in diesel. The water along with the various impurities will settle as a bottom layer and pure diesel is removed from the top layer. The diesel may need further treatment to completely dry it.

Question 20

What other potentially valuable products are obtained from the final mixture?

Answer 20

Once refined of impurities (ie catalyst, soap and excess alcohol) glycerol becomes a valuable co-product of the transesterfication process

Question 21

In many industries in the past, waste materials were simply incinerated. What possible environmental impacts would this have had?

Answer 21

This would have caused air pollution as a result of incinerating waste, resulting in photochemical smog (due to the release of volatile organic compounds and oxides of nitrogen) and acid rain (due to the release of oxidise of sulfur and nitrogen)

Question 22

How can locally sourced resources reduce the environmental impact of an industrial process?

Answer 22

Using nearby resources reduces the requirement to transport large quantities of materials over large distances, which consumes a large amount of energy.

Question 23

Why is the use of catalysts integral to green chemistry?

Answer 23

Catalysts allow reactions to use less energy and to proceed at a rate that does not necessitate high concentrations, thereby using fewer resources.

Question 24

Why could changing to a ‘greener’ chemical synthesis make good economic sense for a company?

Answer 24

Storing, treating and disposing of waste costs significant amounts of money. Reducing the amount of waste produced would reduce running costs, thereby increasing profit margins. Also, using renewable materials means that production would not have to cease once a finite starting resource has been exhausted.

Question 25

What attributes would be required for an alternative chemical synthesis to be considered ‘green synthesis’?

Answer 25

Use fewer reagents, generate less waste, and use renewable materials and be more energy efficient

Question 26

Describe the principle of minimise the potential for accidents

Answer 26

Design chemical and their forms (solid, liquid or gas) to minimise the potential for chemical accidents, including explosions, fires and releases to the environment.

Question 27

Describe the principle of analyse in real time to prevent pollution

Answer 27

Include continuous monitoring and control during the process to minimise or eliminate the formation of by-products

Question 28

Describe the principle of design chemicals and products that are biodegradable

Answer 28

Design chemical products that break down to harmless substances after use, so that they do not accumulate in the environment

Question 29

Describe the principle of increase energy efficiency

Answer 29

Minimise energy requirements. Perform chemical reactions at room temperature and pressure whenever possible

Question 30

Describe the principle of use safer solvents and reaction conditions

Answer 30

Avoid using toxic solvents to dissolve reactants or extract products

Question 31

What is retrosynthetic analysis?

Answer 31

product is identified and chemists work backwards to choose the necessary reactants.

Question 32

What do you need to consider when deciding on the steps for multiple chemical reactions? (4)

Answer 32

Availability and cost of reactants
Conditions required, such as temperature and pressure
Other chemical required, including catalysts
Side reactions that may occur, producing unwanted products

Question 33

What is a linear pathway?

Answer 33

When a product is formed by starting with product A, using that to form B, then using B to form C and so on.

Question 34

What is a convergent pathway?

Answer 34

Two chemicals are made in independent reactions then combined to make the desired product

Question 35

What is one factor that limits the theoretical yield?

Answer 35

the limiting reactant

Question 36

What is the fermentation equation?

Answer 36

C6H12O6(aq) -> 2C2H5OH(aq) + 2CO2(g)

it is anaerobic reaction

Question 37

Atom economy=

Answer 37

mass of atoms in the desired product/ mass of atoms in the reactants X 100

Question 38

What are the first step of the purification of biodiesel? (2)

Answer 38

Biodiesel is then washed with warm water to remove any residual methanol, catalyst, glycerol or soap it may contain. Impurities are very soluble in water while water is insoluble in diesel.
The water along with the various impurities will settle as a bottom layer and pure diesel is removed from the top layer. The diesel may need further treatment to completely dry it.

Question 39

What is the second step of the purification of biodiesel?

2

Answer 39

Biodiesel is then washed with warm water to remove any residual methanol, catalyst, glycerol or soap it may contain.
Impurities are very soluble in water while water is insoluble in diesel. The water along with the various impurities will settle as a bottom layer and pure diesel is removed from the top layer. The diesel may need further treatment to completely dry it.

Question 40

Does biodiesel dissolve in glycerol?

Answer 40

no as biodiesel is non-polar which glycerol is polar.

Question 41

What happens if the base to triglyceride ratio approaches 3:1?

Answer 41

It produces soap molecules. If excess soap molecules is present them it allows micelles to stabilise each substance in the other and so the two liquids will mix and form an emulsion, significantly increasing the amount of time needed for the mixture to be distilled and may decrease the yield.