Gree n Chemist Ry

GreeGreennChemistChemistryry

Green ChemistryGreen Chemistry

• IntroductionIntroduction• Percentage yield vs. atom economyPercentage yield vs. atom economy• The 12 principles of green chemistryThe 12 principles of green chemistry• Application of green chemistry in practiceApplication of green chemistry in practice• Feasibility of green chemistry for daily lifeFeasibility of green chemistry for daily life

IntroductionIntroduction

What is green chemistry?What is green chemistry?• Green chemistry is the use of chemistry for Green chemistry is the use of chemistry for

prevention of pollution problemsprevention of pollution problems. It involves the . It involves the design of chemical products and processes that are design of chemical products and processes that are environmentally benignenvironmentally benign. Green chemistry covers . Green chemistry covers all aspects and types of chemical processes that all aspects and types of chemical processes that reduce negative impacts to human health and the reduce negative impacts to human health and the environmentenvironment..

• Green chemistry can be used in the following areas:Green chemistry can be used in the following areas: • AerospaceAerospace• AgriculturalAgricultural• AutomotiveAutomotive• BiotechnologyBiotechnology• Ceramics and MaterialsCeramics and Materials• ChemicalChemical• CommunicationsCommunications• Computer SystemsComputer Systems• Consumer ProductsConsumer Products• Dyes and PhotographyDyes and Photography• EducationalEducational• Electronics and Electrical EquipmentElectronics and Electrical Equipment• EnvironmentalEnvironmental• Food and BeverageFood and Beverage• Homeland SecurityHomeland Security• LeatherLeather• MedicalMedical

Percentage yield and Percentage yield and atom economyatom economy

Percentage yieldPercentage yield

It does not indicate how efficiently the reactants have been used in generating the desired product.

% Yield = Actual yield x 100% Theoretical yield

Calculating Percentage (%) YieldCalculating Percentage (%) Yield2.3g of sodium reacts with an excess of chlorine to produce 4.0g of sodium chloride.

(Ar reactants: Na=23 Cl=35.5 Mr product: NaCl= 58.5)

58.5 x 0.1 = Theoretical yield of NaCl = 5.85g

What is the percentage yield?


= 4.0g x 100% = 5.85g

68%

2Na(s) + Cl2(g) 2NaCl(s)

2.3g Na = 2.3 mol Na23

= 0.1 mol Na

Theoretically 0.1 mol Na should yield 0.1 mol NaCl

Calculating Percentage (%) YieldCalculating Percentage (%) YieldIf 1.2g of magnesium reacts with an excess of oxygen to produce 0.8g of magnesium oxide… What is the percentage yield?

% Yield = 0.8g x 100% = 2g

40%

2Mg(s) + O2(g) 2MgO(s)

(Ar reactants: Mg=24 O=16 Mr product: MgO= 40)

1.2g Mg = 1.2 mol Mg24

= 0.05 mol Mg

Theoretically 0.05 mol Mg should yield 0.05 mol MgO

40 x 0.05 = Theoretical yield of MgO = 2g


Calculating Percentage (%) YieldCalculating Percentage (%) YieldIf 2g of calcium carbonate reacts with an excess of hydrochloric acid to produce 1.11 g of calcium chloride….

What is the percentage yield?

% Yield = 1.11 x 100 = 2.22

50%

2HCl + CaCO3 H2O + CO2 + CaCl2

(Mr values are: CaCO3 = 100 CaCl2 = 111)

2g CaCO3 = 2 mol CaCO3100

= 0.02 mol CaCO3

Theoretically 0.02 mol CaCO3 should yield 0.02 mol CaCl2

111 x 0.02 = Theoretical Yield of CaCl2 = 2.22g


2008-Al Chem Paper II2008-Al Chem Paper II5(a) Upon irradiation of visible light, 0.450g of 2-4-dimethylpentan

e undergoes monochloro-substitution to gives 0.200g of 1-chloro-2,4-dimethylpentane. 0.167g of 2-chloro-2,4-dimethylpentane and 0,117g of 3-chloro-2,4-dimethylpentane.

(ii)(I) calculate the overall percentage yield for the monchlorinated products formed.

ANSTotal no. of moles of monochloroinated products = (0.2+0.167+0.117)/134.5= 3.60X10-3 No. of moles of 2-4-dimethylpentane = 0.45/100 = 4.5X10-3 Overall % yield = 3.60X10-3/4.5X10-3 = 80

1998-Al Chem Paper I1998-Al Chem Paper I

8(b) 20.0g of 4-nitrobenzoic acid reacted with PCl5 to give a product which reacted exothermically with ammonia to give T. After treatment with Br2 and NaOH(aq), T gave a soild. Crystallization of the soild from ethanol gave 9.3 g of U( C5H6N2O2)

(i)Calculate the % yield of U from 4-nitrobenzoic acid

ANSMolar mass of C7H5NO4 =167.12Molar mass of C5H6N2O2 = 138.128% yield = 9.3X 167.12 X100% 20.0X138.128 = 56.3%

Yield is not enough, because it

•Ignores auxiliaries (reagents, catalysts, solvents, etc.)•Ignores work-up and purification•Ignores energy used, hazards involved, and any toxic chemicals used or produced.

Sustainable Development and Atom Economy

the reaction may be reversible (the reactants might not be converted completely into the products)

the reaction may produce unexpected products

the products cannot be efficiently separated from the reactants

Sustainable Development and Atom EconomySustainable Development and Atom Economy

Developing chemical reactions with a high atom economy is therefore crucial in moving towards sustainable development. High atom economy also makes good economic sense. However, some chemical reactions have a limited atom economy because:

The atom economy is measure of the conversion of starting material (reactant) into desired product. It is different from percentage yield.

The atom economy is measure of the conversion of starting material (reactant) into desired product. It is different from percentage yield.

Sustainable Development and Atom EconomySustainable Development and Atom Economy

In an In an idealideal reaction, all the atoms of the reactants reaction, all the atoms of the reactants would end up as useful product. Such a reaction would end up as useful product. Such a reaction would produce no waste at all, but this is rarely would produce no waste at all, but this is rarely possible.possible.

Calculating Atom EconomyCalculating Atom Economy

The atom economy (also called atom utilisation) of a reaction, is a measure of the percentage of the starting materials that actually end up as useful products.

The atom economy can be calculated in the following way:

% atom economy = mass desired product(s) x 100% total mass of reactants

Calculating Atom EconomyCalculating Atom Economy

NH3(g) + HNO3(aq) NH4NO3(aq)

ammonia + nitric acid ammonium nitrate

In the production of ammonium nitrate...

…17g of NH3 and 63g of HNO3 produce 80g of NH4NO3

Calculate the atom economy for this reaction:

NH3= 17g HNO3 = 63g NH4NO3 = 80g

Atom economy = 80g80g

x 100 = 100%

As there are no waste products in this reaction, it has an atom economy of 100%.

Calculating Atom EconomyCalculating Atom EconomyExample 2:

iron oxide + carbon iron + carbon dioxide

In the smelting of iron:

…for every 320g of iron oxide 224g of iron is produced.

Calculate the atom economy for this reaction:

2Fe2O3= 320g 3C= 36g 3CO2 = 132g

Atom economy = 224g320 + 36g

x 100 = 63%

As the reaction produces carbon dioxide as a waste product, the reaction can not have an atom economy of 100%. The atom economy of this reaction could be improved, if a use could found for the waste carbon dioxide.

4Fe= 224g

2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)

Atom Economy and Percentage YieldAtom Economy and Percentage Yield

Nitrogen reacts with hydrogen to make ammonia.

N2 + 3H2 2NH3

a) Calculate the maximum theoretical mass of ammonia that can be made by reacting 90g of hydrogen with an excess of nitrogen.

b) In the reaction, only 153g of ammonia was produced. Calculate the percentage yield.

c) Calculate the atom economy to make ammonia from the reaction of nitrogen and hydrogen.

a) Calculate the maximum theoretical mass of ammonia that can be made by reacting 90g of hydrogen with an excess of nitrogen.

number of moles of H2 = 90/2 = 45moles

number of moles of NH3 = 2/3 x 45 = 30 moles

Maximum theoretical mass

= 30 x (14+3) = 510 g

b) In the reaction, only 153g of ammonia was produced. Calculate the percentage yield.

Percentage yield = (153/510) x 100% = 30%

c) Calculate the atom economy to make ammonia from the reaction of nitrogen and hydrogen.

Atom economy = 100% (since all the reactants converts to products)

Conclusion: Conclusion: High atom economy is not equal to high percentage yield.High atom economy is not equal to high percentage yield.

Reaction Type Description Atom Economy

AdditionAddition Different molecules join together to make a new substance

100% as all reactant atoms end up in the product

CondensationCondensation Two molecules join, with the production of a small molecule like water or ammonia

Always a little less than 100% as small molecules are produced, which are usually waste.

EliminationElimination A group of atoms is removed from a molecule, usually leaving a double or triple bond

Generally poor because an additional product is always formed

RearrangementRearrangement Atoms are rearranged to create a different substance with the same empirical formula

100% as the same atoms are present in the product as in the reactant

SubstitutionSubstitution A group of atoms on a molecule is replaced by a different group

The group replaced creates a product too, but as this may vary considerably, substitutions can be from fairly good to very poor

The 12 principles of green chemistryThe 12 principles of green chemistry

1. Prevent waste

2. Design safer chemicals and products

3. Design less hazardous chemical syntheses

4. Use renewable feedstocks

5. Use catalysts, not stoichiometric reagents

In 1998, the 12 principles of green chemistry were articulaIn 1998, the 12 principles of green chemistry were articulated by Anastas, P. T. & Warner, J.C. in the book ‘Green ted by Anastas, P. T. & Warner, J.C. in the book ‘Green Chemistry: Theory and practice.’Chemistry: Theory and practice.’

6. Avoid chemical derivatives7. Maximize atom economy 8. Use safer solvents and reaction conditions9. Increase energy efficiency 10. Design chemicals and products to degrade

after use11. Analyze in real time to prevent pollution 12. Minimize the potential for accidents

Applications of Applications of green chemistrygreen chemistry

Microscale ExperimentMicroscale Experiment

• a teaching method widely used at school and at university levels, working with small quantities of chemical substances

• use low-cost and even no-cost material

• less starting materials are required for testing the possibility of some unknown reactions

• very useful when the starting materials are very expensive• less reactant, less reagent and less solvent are required• lower cost• save time and money• use small amount of reactants can make the experiment

more safe• less chemical waste is deposited

Advantages of Microscale ExperimeAdvantages of Microscale Experimentnt

• equipment and textbooks about microscale experiment are • but the costs can be recovered in a relatively short period o

f time due to savings realized on purchase and disposal costs of reduced quantities of chemicals

Disadvantages of Microscale ExperiDisadvantages of Microscale Experimentment

Use of hydrogen peroxide as a Use of hydrogen peroxide as a bleaching agentbleaching agent

• Traditional chlorine bleach(active ingredient – hypochlorite OCl

-)

• Disadvantages:Disadvantages:1. Toxic chlorine gas may evolve

2NaOCl + 2NH3 2NaONH3 +Cl2

2. Poisonous chlorinated organic compounds may be found3NaOCl +NH3 3NaOH +NCl3

3.The reaction of byproducts hydrazine and monochloramine is highly exothermic NH3 + NaOCl NaOH + NH2Cl

NH3 + NH2Cl + NaOH N2H4 + NaCl +H2O

• Bleached by oxidation :H2O2(aq) + dye H2O(l) + (dye+O)

ApplicationApplications:s:• bleaching agent for hair • the bleaching of pulp for paper manufacturing• household disinfectant

• Hydrogen peroxide should be stored in a cool, dry, well-ventilated area and away from any flammable or combustible substances, it should be stored in a container composed of non-reactive materials such as stainless steel or glass

Use of fuel cellUse of fuel cell

• It is a device that converts fuel i.e. hydrogen into electrical energy

• The cell, the reactants flow in and products flow out electrolyte in the presence of electrolytes such as H2SO4

• The anode and cathode are coated with Pt, which acts as a catalyst.At anode : 2H2 4H

+ +4e

-

At cathode : O2 + 4e- + 4H

+ 2H2O

• The elctrons produred at the anode flow through the wire connecting the external circuit, electrical energy is generated

• At the end, pure water and heat are produced.

Advantages of using H-cell:Advantages of using H-cell:• they are environmentally friendly • no air pollutants are emitted• do not contribute to global warming as combustion of

fossil fuel is not involved• high efficiency• hydrogen is the most plentiful element in the universe

ApplicationApplicationss of H-cell: of H-cell:• fuel cell vehicles (still in development stage)• electrical system of rockets and shuttles

Manufacture of nylon-6,6 by Manufacture of nylon-6,6 by Beckmann rearrangementBeckmann rearrangement

oxime lactam Monomer for nylon-6

• a typical Beckmann rearrangement• The oxime from cyclohexanone has identical carbonyl sub

stituents and exists as a single isomer• The product of the rearrangement is a lactam (a cyclic a

mide), which can be hydrolyzed to an omega-amino acid • This lactam serves as an important industrial precursor t

o nylon-6

AdvantagesAdvantages• no wastage• water is a renewable source• rearrangement – 100% atom economy

Obtain saturated fats by catalytic Obtain saturated fats by catalytic hydrogenationhydrogenation

• adds hydrogen atoms at the double bonds of a fatty acid chain to produce an artificial fatty acid

• operate at pressures of 3 – 6 atm and temperatures of 100 – 180oC

• using nickel / palladium / nickel / rhodium as catalysts

Advantages of using catalytic hydrogenationAdvantages of using catalytic hydrogenation• cheaper than animal source fats• are available in a wide range of consistencies• increased oxidative stability• longer shelf life• a harder consistency• a higher melting point• better oxidation stability

Ionic liquidIonic liquid

• Ionic liquid is used to refer to a molten salt that is a liquid at ambient temperatures. They generally are compounds that have both a large anion and cation, and possess a low degree of symmetry.

Fig. 1 Examples of simple room temperature ionic liquid

Ionic liquids can be:• simple salts, or• binary ionic liquid

Example• 1-alkyl-3-methylimidazolium tetrafluoroborate salts are

miscible with water at 25 °C where the alkyl chain is less than 6, but at or above 6 carbon atoms, they are form a separate phase when mixed with water.

• This makes solvent extraction easier.

AdvantagesAdvantages• Prevent waste• Use renewable feedstocks• Use catalysts, not stoichiometric reagents• Avoid chemical derivative

BiofuelsBiofuels

• Fuels derived from organic biomass from recently living animals or plants or their byproducts, has transformed from a niche alternative to fossil fuels.

• Vegetable oils, animal fats, ethanol and biodiesel are biofuels.

• Landfill sites generate gases by anaerobic digestion. Landfill gas contains approximately 50% methane, the gas found in natural gas.

• Ethanol is produced by enzyme digestion fermentation of the sugars, distillation and drying.

AdvantagesAdvantages• Prevent waste

• Use renewable feedstocks

• Design chemicals and products to degrade after use

Haber process in the manufacture of Haber process in the manufacture of ammoniaammonia

• Area: Chemical + Ceramics and Materials• N2(g) + 3 H2(g) 2 NH3(g) (ΔH = −92.4 kJ·mol−1) • catalyst: a form of magnetite, iron oxide

• Preparation:• First, methane is cleaned to remove sulphur impurities t

hat will poison the catalysts.• Steam reforming: over a catalyst of nickel oxide

(CH4 + H2O → CO + 3 H2 )• Secondary reforming: addition of air to convert the met

hane that did not react during steam reforming.CH4 + O2 → 2 CO + 4 H2

CH4 + 2 O2 → CO2 + 2 H2O• Then the water gas shift reaction yields more hydrogen f

rom CO and steam.CO + H2O → CO2 + H2

• Last step: the gas mixture passing into a methanator, which converts most of the remaining CO into methane for recycling as carbon monoxide poisons the catalyst

CO + 3 H2 → CH2 + H2O

Use of supercritical carbon dioxide Use of supercritical carbon dioxide (e.g. decaffeinating coffee)(e.g. decaffeinating coffee)

Critical temp. (31.1 °C) and critical pressure (72.9 atm/7.39 Mp

a) are low

• In a fluid state while also being at or above both its critical temperature and pressure

• Yields rather uncommon properties, e.g. dissolving organic substances

• Low toxicity and environmental impact• An important commercial and industrial solvent• It replaces a chlorinated organic solvent tetrachloroethe

ne (Cl2C=CCl2) which may cause cancer in dry cleaning, metal cleaning and other polluting industrial processes.

HH22OO22 and O and O22 as environmentally beni as environmentally beni

gn oxidising agentsgn oxidising agents

• Many industrial processes involves oxidising agents, e.g. KMnO4, K2Cr2O7, conc. NHO3, etc.

• These oxidising agents are not green.

• Conc. NHO3 on reduction produces toxic N2O, which induces greenhouse effect and leads to ozone depletion

• H2O2 is one of the green replacement for these harmful oxidisng agents

• Aqueous hydrogen peroxide is an ideal oxidant, because the atom economy is excellent and water is the only theoretical side product

H2O2 [O] + H2O or 2H2O2 O2 + 2H2O

• Example• Cyclohexane is converted directly to pure, crystalline he

xanedioic acid in a very high yield

• Molecular oxygen is another environmental benign oxidising agent which has been used industrially, e.g.

RCH2OH RCOOH

• The product from the reduction of O2 is environmentally benign water

O2, catalyst, sunlight

BioplasticBioplastic

• Bioplastics (also called organic plastics) are a form of plastics derived from renewable biomass sources, such as vegetable oil, corn starch, or microbiota, rather than fossil-fuel plastics which are derived from petroleum.

• On the other hand, bioplastic can be made from agricultural byproducts and also from used plastic bottles and other containers using microorganisms.

Plastics made from corn are already on the market.

Advantages of bioplastic:Advantages of bioplastic:• Because of their biological degradability, the use of biopl

astics is especially popular for disposable items, such as packaging and catering items.

• In these areas, the goal is not biodegradability, but to create items from sustainable resources.

• The production and use of bioplastics relies less on fossil fuel as a carbon source and also introduces fewer greenhouse emissions if it biodegrades. They significantly reduce hazardous waste caused by oil-derived plastics, which remain solid for hundreds of years.

Disadvantages of bioplastic:Disadvantages of bioplastic:• There are fears that bioplastics will damage existing recy

cling projects. • Shelf life is limited because the plastic is permeable to w

ater - the bottles lose their contents and slowly deform.

Catalytic converterCatalytic converter

• used to reduce the toxicity of emissions from an internal combustion engine

• used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped machines

• provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances



Types of catalytic converter:Types of catalytic converter:

• Two-way

• Three-way

Two-way catalytic converterTwo-way catalytic converter

• There are two simultaneous tasks :

• Oxidation of carbon monoxide to carbon dioxide :

2CO + O2 → 2CO2

• Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water :

CxH2x+2 + 2xO2 → xCO2 + 2xH2O

• (a combustion reaction)

• Widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions

• However, cannot control amount of nitrogen oxides NOx

• There are three simultaneous tasks :

• Reduction of nitrogen oxides to nitrogen and oxygen : 2NOx → xO2 + N2

• Oxidation of carbon monoxide to carbon dioxide :

2CO + O2 → 2CO2

• Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water :

CxH2x+2 + 2xO2 → xCO2 + 2xH2O

Three-way catalytic converterThree-way catalytic converter

• Three-way catalytic converters can store oxygen from the exhaust gas stream, when the air fuel ratio goes lean

• When oxygen is insufficient, the stored oxygen is released and consumed

• Unwanted reactions : formation of hydrogen sulphide and ammonia

• But can be limited by precious metals used

• Nickel or manganese is added to block the adsorption of sulphur by the washcoat

Three-way catalytic converterThree-way catalytic converter

• Most commonly used catalytic converter is the diesel oxidation catalyst

• They uses excess O2 in the exhaust gas stream to oxidize CO to CO2 and HC to H2O and CO2

• Reach 90% efficiency, eliminate diesel odor and help to reduce visible particulates (soot)

• However they are incapable of reducing NOx

For diesel enginesFor diesel engines

• Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat the working surfaces

• catalyst cannot contact and treat the exhaust• The most notable contaminant is lead, so vehicles equipped

with catalytic converters can only be run on unleaded gasoline.

• Other common catalyst poisons : manganese, silicon, phosphorus, zinc

Catalyst PoisoningCatalyst Poisoning

• Catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time

• The increased exhaust temperature can sometimes liquefy or sublimate the contaminant, removing it from the catalytic surface

• However, removal of lead deposits in this manner is usually not possible due to lead's high boiling point

Treatment for Catalyst PoisoningTreatment for Catalyst Poisoning

Potential applicationsPotential applications

(1) Corn waste converted to chemicals

• conversion of glutamic acid to -aminobutyric acid (GABA) (nitrogen-containing)using a decarboxylase enzyme

• producing nitrogen-containing industrial chemicals more cheaply than the energy intensive from the waste from bioethanol production

• improving the green credentials and the economics of biofuel production

(2) Expanding waste to reduce waste

• expanding the structure of waste polyvinyl-alcohol (PVA) from liquid crystal display (LCD) screens to form a mesoporous material with a high surface area

• use of enzyme immobilisation, tissue scaffolds or drug delivery due to the biocompatibility of PVA

• providing an exciting new method for recovering materials that would otherwise go to waste

• iodine, which is present in waste PVA, is essential for the expansion process

Feasibility of green chemistry for Feasibility of green chemistry for daily life applicationsdaily life applications

• A number of difficulties involves:• Chemical (what technologies are available?)• Economic (who pays, who benefits?)• Social (who are affected?)• Political (who is responsible?)

• Possible contribution of green chemistry in achieving sustainability in the 21st century:

• (1) Renewable energy technologies

E.g. Array of solar cells to supply electric power to space shuttle

• (2) Reducing our dependence on the dwindling fossil carbon

• (3) The replacement of existing polluting technologies by environmentally benign alternatives

Past Paper Past Paper AnalysisAnalysis

(05, 07, 08)(05, 07, 08)

Past Paper 05 II 5.(a)(iii)Past Paper 05 II 5.(a)(iii)

Besides cutting down petroleum consumption, suggest one additional advantage of using the alternative fuel over using gasoline. (1M)

• Gasoline (petrol) is commonly used as motor car fuel.• Lead petrol: Straight chain alkanes cause knocking

(死火 ) in the engine when they are burnt as oxygen is used up very quickly for complete combustion.

• The problem is solved by adding tetrathyllead (TEL) >> leaded petrol (Toxic to human, was ban by the HK government since 1994.)

• Unlead petrol: Straight chain alkanes >> branched chain

Additional Information:Additional Information:Past Paper 05 II 5.(a)(iii)Past Paper 05 II 5.(a)(iii)

Ans:

Alternative fuel produces less air pollutants than petroleum when burn.

Past Paper 05 II 5.(a)(iii)Past Paper 05 II 5.(a)(iii)

Past Paper 07 I 8.(a)(i)Past Paper 07 I 8.(a)(i)

(2M)

Ans:

Past Paper 07 I 8.(a)(i)Past Paper 07 I 8.(a)(i)

Past Paper 07 I 8.(a)(Past Paper 07 I 8.(a)(iii)i)

(1M)

Past Paper 07 I 8.(a)(Past Paper 07 I 8.(a)(iii)i)

Ans:

Past Paper 07 I 8.(a)(Past Paper 07 I 8.(a)(iiiii)i)

(1M)

Past Paper 07 I 8.(a)(Past Paper 07 I 8.(a)(iiiii)i)

Ans:

Past Paper 08 I 10.Past Paper 08 I 10.

(20M)

10. Write an essay on the application of the principles of green chemistry in industry.

Ans: Past Paper 08 I 10.Past Paper 08 I 10.

• Supercritical carbon dioxide:• carbon dioxide that is in a fluid state while also

being at or above both its critical temperature and pressure, yielding rather uncommon properties

• usually as a gas in air at standard conditions for temperature and pressure / as a solid called dry ice when frozen


Additional Information:Additional Information:

Additional Information:Additional Information: Phase diagramPhase diagram


- if temperature & pressure are both increased from standard conditions for temperature and pressure to be at or above the critical point for carbon dioxide

>> adopt properties midway between a gas and a liquid

- behaves as a supercritical fluid above its critical temperature (31.1 °C) and critical pressure (72.9 atm), expanding to fill its container like a gas but with a density like that of a liquid



- low toxicity and environmental impact - is becoming an important commercial and industrial

solvent - relatively low temperature of the process and the

stability of CO2 also allows most compounds to be extracted with little damage or denaturing



Ans:


Past Paper 08 I 10.Past Paper 08 I 10.Ans:

End of presentation

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