green chemistry pack 2

7/22/2019 Green Chemistry Pack 2

1/34

GGRREEEENNCCHHEEMMIISSTTRRYYUnit 2.13 (p236-247 in AS Chemistry textbook, p108-

114 in CGP AS Chemistry revision guide for Edexcel)

Global warming and climate change

NEED to know

The greenhouse effectis a vital factor in keeping our planet warmenough for us to live on it.

The Sun emits electromagnetic radiation mostly as visible light, UV

radiation and infrared (IR) radiation.

When this solar radiation reaches the Earths atmosphere the UV

and IR radiation is mostly absorbed by atmospheric gases and some

is reflected back into space from clouds.


2/34

Visible light, IR and UV radiation reaching the Earths surface canbe reflected back into space (especially from light-coloured surfaces

such as snow) but the rest is absorbed by the Earth, which heats up.

The Earth radiates energy back out to space as IR radiation (heat).Gases in the atmosphere can absorb some of this IR radiation and

re-emit it in all directions. Some gets back to Earth again and keeps

us warm.

This is called the greenhouse effectbecause gases in the atmosphere act

like the glass in a greenhouse, trapping some of the energy. If this didnt

happen and almost all the energy was lost to space, the Earth would be

about 30C cooler and we wouldnt be able to live here.

The table below shows the relative greenhouse factor and the global

warming potential for some of the most common greenhouse gases.

Greenhouse gas Formula Relative

greenhouse

factor

Global warming

potential

Carbon dioxide CO2 1 1

Methane CH4 30 20

Dinitrogen

oxide

N2O 200 300

Typical CFC E.g. CCl3F 21000 6500

Definition:Gases which contribute to the greenhouse effect are called greenhouse

gases and are classified according their relative greenhouse factors. This term

allows a comparison of the effect they will have on global warming. It is calculated

by comparing the effect gases have in absorbing IR radiation relative to the effect

of carbon dioxide, the most common greenhouse gas. The global warming

potential of a gas is calculated by combining their relative greenhouse factor(ability to absorb IR radiation) and their half-life in the atmosphere (how long they

take to break down). It is a better measure of the true effects of releasing a gas into

the atmosphere over its whole lifetime.


3/34

The effect of humans burning fossil fuels and adding greenhouse

gases to the atmosphere is causing anthropogenic climate change.

Of course, the climate sometimes changes on earth naturally (for

example the Ice Ages which wiped out woolly mammoths), due toprocesses such as the dissolving of carbon dioxide in seawater, plant

growth or solar activity, so it can be difficult to work out how much

of the change is due to humans.

Scientists think some human activities are particularly bad for the

atmosphere, such as air travel. High-flying jet aircraft produce frozen

water vapour trails called contrails. Although these are only water

they might be contributing to changes in the atmosphere as more

clouds may reflect more energy out of the Earths atmosphere.

Aircraft engines also produce nitrogen oxides which are greenhouse

gases and can destroy ozone in the upper atmosphere which

protects us (there is more about this later in this unit).

EXTENSION AND EXPERIMENTS: How science works

How do we tell if humans are causing climate change? This is quite a

difficult question to answer because the Earths climate system is very

complicated, and scientists are debating this question all the time. But

most scientists now agree that human activity is having a large effect onthe climate of our planet and is causing it to warm up, largely by

increasing the amount of carbon dioxide in the atmosphere. Lets have a

look at the evidence used to investigate this question.

In order to see if the climate is changing, we need to look at what it did in

the past. In order to work this out, scientists can use tree rings to work

out the temperature of the planet in the past (because trees grow widerrings in their trunk in years with a high temperature). We can also use ice


4/34

cores (drilled from the Antarctic or Greenland ice sheets) to look at the

composition of the atmosphere in the past, because trapped bubbles of

air are found in the ice cores, and the air can be extracted and analysed.

This technique allows us to look very far in the past because scientists cantake very deep ice cores, reaching ice which was set down a long time

ago. We can also use historical records taken by people in previous

centuries, and from the 20th

century we have very good records from

weather and climate monitoring stations, which record details about the

climate in a particular area. Satellites provide very detailed data about

the exact composition of the atmosphere over the whole globe.

Using all these techniques, scientists have pieced together a picture of

what the climate and atmosphere was like over thousands of years:

You can see that changes in carbon dioxide levels are followed very

closely by changes in temperature. The main piece of evidence for


5/34

anthropogenic climate changeis that normally in the past, large changes

in temperature or carbon dioxide levels have only occurred very slowly

(normally over thousands of years). However, recently levels of carbon

dioxide and temperature have peaked very sharply, which does not fit theprevious pattern. The large increase over the last century is therefore

very likely to be due to human activities. Apart from this, the overall level

of CO2in the atmosphere is a concern because it is higher now than for

many millions of years. Although carbon dioxide is slowly removed from

the atmosphere (for example by dissolving in sea water and marine

sediments, and being absorbed by plants, which might eventually make

fossil fuel) most scientists are concerned that we are adding CO2to theatmosphere much more quickly than it can be removed. This could lead

to species becoming extinct and the ice caps melting, as well as causing

problems for people. A more unpredictable climate would be bad for

everyone!

Quick Questions

1. Carbon dioxide has a lower relative greenhouse factor than othergases. Why is it so significant when considering global warming and

climate change?

2. How can we tell the difference between natural and anthropogenicclimate change?

3. Greenhouse gases are the major cause of anthropogenic climatechange.

a. Name three greenhouse gases. (2 marks)b. Explain how greenhouse gases keep the temperature in the

lower layer of the Earths atmospherehigher than it would

otherwise be. (3 marks)

c. What factors affect the contribution a gas makes to thegreenhouse effect? (2 marks)


6/34

Carbon neutrality and carbon footprint

NEED to know

When thinking about whether a process or fuel is carbon neutral it isimportant to remember all the stages in its production. For instance at

first glance you might think that a wind farm would be carbon neutral

since it does not produce carbon dioxide directly. However when you

think about the carbon dioxide that was released during the process of

manufacturing the wind turbine and transporting it to the right place, as

well as making the infrastructure that supports delivery of the electricity

from the wind farm to homes, the situation is not so clear.

Some companies or individuals try to reduce their carbon footprint by

carbon offsetting, a process in which a project is put in place to be a net

sink of carbon, to make up for emissions. This could be building a

renewable energy source such as a solar or wind farm, or planting new

trees. But some companies have also tried to do this by carbon trading,

Definition:A fuel or process is carbon neutralif the carbon dioxide released in

using/doing it is the same as the carbon dioxide that was absorbed when it was

formed. Usually this definition is modified to include the idea that the fuel must be

able to be formed within a reasonable length of time, so that for example, oil which

can take thousands of years to form is not truly renewable but wood is.

Definition:Your carbon footprintis a measure of how much impact you have on

the environment in terms of greenhouse gases released. This is usually calculated

as tonnes or kilograms of CO2released (taking into account the global warming

potential of different greenhouse gases that might be released) in a process (or for

a fuel in g/kJ). The carbon footprint can be calculated for any individual, business or

process. An individuals carbon footprint is often calculated over a year.


7/34

whereby they pay some other company or individual to release less

carbon and the carbon footprint simply balances overall.

You should know about the reactions of CFCs and HCFCs with ozone,

which lead to the depletion the ozone layer. This is separate from their

effect as greenhouse gases. The ozone layer normally stops harmful

ultraviolet radiation from reaching the Earths surface, so a hole is bad

news! This is the reaction that occurs:

1. Firstly ozone is formed in the atmosphere when UV radiation makesoxygen molecules break up to form oxygen free radicals. The

oxygen free radicals recombine with oxygen to form ozone:

2. CFCs are dissociated by UV radiation to form free radicals:

3. The chlorine free radical reacts with ozone:4. The new chlorate free radical reacts with ozone and produces more

chlorine free radicals:

During this reaction the overall effect is to convert two molecules of

ozone to three molecules of oxygen. The chlorine radicals formed in thereaction are not used up and so are catalytical radicals.One of the main

reasons this reaction is so harmful is that it can form a chain reaction.

Nitrogen oxides also damage the ozone layer by producing NO radicals

which act in the same way:


8/34

In this reaction the NO acts as a free radical catalyst again. Gases such as

CFCs have been gradually phased out and are now usually replaced with

HCFCs which do not break down to form free radicals.


Talking about carbon footprints can be a political issue. Take a look at this

map which plots greenhouse gas emissions per person globally. Most of

the emissions are produced by developed countries, but developing

countries such as India and China with large populations and increasingly

industrial economies might soon overtake this. It does not seem very fairto say to these countries that they cannot enjoy the lifestyle that

countries in Western Europe and North America have enjoyed over the

last half-century. But tackling carbon emissions has to be a global task as

the effects of global warming will harm us all. So what should be done?

First the basic science had to be in place. For example in order to control

gases such as CFCs we first need to know the effects these gases have

very clearly. This was shown by scientists from the British Antarctic

Survey observing the atmosphere. In the 1970s they showed that the

concentration of ozone over the Antarctic was very low compared towhat had been previously measured. They measured it again in 1985 and


9/34

were surprised to find that it was even lower. They checked their

equipment and results to find out if they were right but got the same

result. When they published their results in a scientific journal, other

scientists read it and were very surprised toobut a team looking atsatellite data also found evidence of the ozone hole. They hadnt noticed

it before in their results because their computers ignored measurements

below a certain level and treated them as errors.

Once scientists had worked together to find out the answer (and work

out what was causing the hole in the ozone layer) the political community

had to get involved to help solve the problem. They did this by agreeingan international treaty called the Montreal Protocolof 1989, which

agreed that countries would stop using CFCs and other ozone-destroying

halogenoalkanes by the year 2000. Nowadays scientists have found

alternatives and CFCs are only used in a few applications where there is

no useable alternative.

The same international effort had to be brought to bear on the carbondioxide emissions problem. Again this was dealt with by an international

agreement called the Kyoto Protocol. Adopted by 37 countries in 1997,

this agreement recognised that not all countries contribute to global

warming equally and tried to reach a fair solution. A target of just over 5%

reduction in greenhouse gas emissions compared to 1990 levels, by the

year 2012, was agreed for developed countries, mostly in Europe and

North America. It was also agreed that other countries would also try to

reduce their emissions on a voluntary basis, and that developed countries

would try to help developing countries with this target, for instance by

giving advice and donating expertise and money to green technology and

the development of green energy resources in these countries.


10/34

Quick Questions

1)Decide whether you think these fuels are really carbon neutral andgive your reasons:a) Petrol (1 mark)b)Hydrogen made from reforming methane (1 mark)c) A biofuel such as bioethanol (1 mark)d)Solar-power (photovoltaic cells) (1 mark)If you had to pick the most carbon neutral one of these fuels to power

a device, which would you choose? Apart from the emissions involved,

what other considerations do people have when picking a fuel?

(3 marks)

2)CFCs were invented in 1928. They were widely used in the 20thcenturyand are now being phased out.

a) What are the useful properties of CFCs? Name three typical uses forthese compounds. (6 marks)

b)Why was the use of CFCs banned by the Montreal Protocol?(1 mark)

c) Write out the reactions of CCl3F which lead to ozone depletion.(6 marks)

3)Do you think it is fair that some companies try to reduce their carbonfootprint by carbon trading? What problems can you see with this

system? (2 marks)


11/34

Reducing hazards and pollution in the chemical

industry

NEED to know

The modern chemical industry is trying to become greener by controlling

the pollution it makes, using less energy and using fewer finite resources.

One of the main problems is the disposal of solid waste. Many materials

can be recycled or re-used, such as glass, metal or paper. It is often much

cheaper and uses much less energy to recycle resources than make new

ones. For example, recycling aluminium means that the process ofextracting the aluminium by electrolysis does not need to be repeated,

and it also reduces the emission of PFC (perfluorocarbon) gases, which

are potent greenhouse gases.

If a material cannot be recycled, it must be disposed of, usually either by

incineration(combustion) or in landfill sites. Incineration produces

carbon dioxide and sometimes harmful materials such as dioxins, but it

has the advantage of producing heat which can be captured and used in

energy-recovery systems such as for heating a building. Landfill sites get

used up, and the waste can take a long time to be broken down by

bacteria in the soil. The other problem with landfill is that it produces

methane, which can be explosive and is a greenhouse gas. In order to

stop this happening, methane can be recovered from the site and used as

fuel, although this can be difficult. Sometimes it is just burned to produce

waste heat, but usually we would try to use this heat for something

useful.

Waste water which has been contaminated with pollutants cannot legally

be dumped straight into rivers or the sea, so chemical factories often

have to develop technologies to filter and purify the water and special

tanks to store it in. Waste gases include sulphur dioxide, which causes

acid rain and is a greenhouse gas. There are now controls in place whichset maximum concentrations that can legally be released into the


12/34

atmosphere. Often acidic gases are removed from flue gases by reacting

with limestone:

The result of this reaction (and of burning methane and many other

common reactions) is the release of carbon dioxide. Although this does

not have cause acid rain it is still a greenhouse gas so we would also like

to reduce the amount of carbon dioxide released. One way of doing this is

carbon capture (and sequestration).

Definition:Carbon captureis the technology which allows carbon dioxide to be

stored somewhere, usually in a liquefied form. There have been suggestions that

we could pump this liquid waste CO21km under the ocean into porous rocks,

where it should remain stable because of the pressure and not cause any further

environmental damage. This process could be done at the same time as drilling for

natural gas or oil, pumping the CO2down instead of gas or oil up.


13/34

This picture shows how the plan to do carbon capture in the Miller oil

fields in the North Sea might look. Natural gas and oil are extracted, and

the carbon dioxide is liquefied in the power plant and pumped back down

a pipeline to the oil rig which can pump it down under mudrock whichforms a good seal to keep the CO2out of the atmosphere, maybe for

millions of years. A trial of this technology has already been used in

France at the Lacq power plant with great success.


Apart from discovering facts about the universe, scientists are ofteninvolved in developing new technologies. In the area of green chemistry

this is particularly true. Scientists are trying to develop new renewable

resources before fossil fuels run out or become too expensive. Its not

just for fuel, because oil is also used to make plastics and to produce

chemicals such as ammonia, nitric acid, benzene, sulphuric acid and

ethanoic acid. Some of the new technologies that have been developed

are:Bio oilfrom wheat: Wheat is renewable as a new source can be

grown each year. A type of oil which can be used for fuel is

produced from the wheat using a process called pyrolysis. The

straw is heated without oxygen so it does not burn, but breaks

down into smaller molecules. This material is then cooled quickly so

it does not react and this bio oil orpyrolysis oil can be used as a

fuel. The by-products (carbon solids and a mix of gases) can also beused at the factory, so this process is relatively carbon neutral.

Ethanol from organic waste: Ethanol (used for many industrial

chemical processes) can be produced by fermentingplant material,

usually using a genetically modifiedbacterium. One such GM

micro-organism is KO11, a bacterium that was developed by the

microbiologist Lonnie Ingram in 1987. The pathways in this

bacterium that normally produce acids have been hijacked in theGM organism to produce ethanol instead. Often this process can be


14/34

performed using a starting material that would normally have been

thrown away, such as corn stalks or rice hulls, so this is very

efficient. This is important because in some cases farmers grow

large areas of crops such as maize to be used for bio-ethanolproduction, but land is also needed to grow food crops for our

increasing world population.

Starchand cellulosefrom plants: Both of these materials are

naturally produced by plants and can be used to make a variety of

materials such as plastic bags, paints, adhesives, insulation and a

fibre called lyocell (used for clothes and household textiles). These

materials have the advantage that they are usually biodegradableunlike equivalent materials made from fossil fuels, and since they

are grown from plants they are renewable.

Quick Questions

1. Explain why plants are a sustainable resource. (1 mark)2. Suggest reasons, apart from cost, that carbon capture might not go

ahead. (2 marks)

3. Why is removing sulphur dioxide from flue gases using limestone not atotal solution to the problem? (1 mark)

4. Suggest two reasons for the decline in the use of fossil fuels in thechemical industry. (2 marks)


15/34

Increasing efficiency in the chemical industry

NEED to know

The development of new catalysts is an important way to improve the

efficiency of a chemical process. You should know from earlier in your

course that a catalyst speeds up a chemical reaction. Finding a more

efficient catalyst will not improve the yield (the proportion of products

made from the reactants) but will allow the same yield to be formed

more quickly. By using a better catalyst sometimes chemists can save

money and energy because they will not need to heat a reaction as much.

Catalysts are not used up in reactions so should last a long time, althoughthey are normally replaced sometimes due to wear and tear.

Try this example: propan-1-ol is produced from 1-bromopropane and

sodium hydroxide. What is the atom economy?

Firstly, write down the equation:

Then work out the molar masses of everything you need for the equation

[using Ar(H) = 1, Ar(C) = 12, Ar(O) = 16, Ar(Na) = 23 and Ar(Br) = 79.9].

Plug them into the equation like this:

Definition:Atom economy is a measure of how efficient a reaction is at turning

reactants into the products wanted (rather than waste products). A reaction with

high atom economy is efficient because it is expressed as a percentage. You need to

know this equation for atom economy:


16/34

This tells you that the majority of the starting materials are turned into

waste rather than the desired product. Even if the yield is 100% (the

reaction proceeds to completion) nearly 2/3 of the mass of the atoms in

the original material would be wasted. If scientists wanted to improve

efficiency in the factory making propan-1-ol they could therefore do this

by finding alternative starting materials which form a reaction with better

atom economy. Adding a catalyst would not change the atom economy

since the same reaction is occurring. Only altering the reaction used

would improve the atom economy.

Another way that chemical engineer can improve efficiency is to think

about the energy used in a chemical factory. This energy may be used forheating reactants to start or maintain a reaction; to provide electricity for

electrolysis processes; to power distillation to separate, purify or

concentrate the products; to heat product material to dry it out; to treat

waste water; and to provide heating and hot water for the workers in the

plant. Making these processes more efficient and using more carbon

neutral and efficient energy sources can help to make the chemical

factory greener. Here are several examples of how chemists improveprocesses by thinking about energy considerations:

Use electricity derived from more carbon-neutral fuel sources

(although this may not be under the control of the plant)

Reduce energy demand to save money and help the environment,

for instance by switching machines off overnight or using less

heating.


17/34

Reduce wasted energy caused by any leaking pipes or taps, andimprove insulation.

Use a heat exchanger to recover energy produced in reactions

which would normally be wasted and simply go up the chimneys.This works by transferring energy from the reaction into water

pipes by conduction, and the energy saved here could be used to

provide heating and hot water for the plant.

Adjust your reaction conditions to use less heat, but keep the

reaction going quickly by using good catalysts or putting it under

pressure. If doing a reaction which uses oxygen, consider using pure

oxygen rather than air, so you are not heating other components inthe air.

Generate your own electricity, ideally from a carbon-neutral source.

Then you do not need to pay transmission costs.

Use microwaves to heat reactions, which speeds up the reaction

massively and can mean catalysts are not even needed. Modern

industrial microwaves work by producing an electric field, causing

polar molecules such as water to line up. The field switchescontinually so the molecules are constantly moving, trying to line

up. Microwave energy is there converted into movement and

therefore thermal energy. The movement of the water molecules

heats up the other molecules around them. This process is much

more efficient than heating with a conventional oven and very high

temperatures can be reached. For example, if a reaction is heated

up by 60C, the rate will increase by 106 times.


You might wonder how scientists know which catalyst to choose for a

particular reaction. Sometimes they find out by accident when a bit of

another molecule contaminates the reaction and it goes faster. But

sometimes chemists search for a new catalyst by trying out differentmolecules, or thinking about how the catalyst is speeding up the reaction


18/34

and trying to guess another molecule that would do the same. An

example of this is the production of ethanoic acid. Firstly, industrial

chemists had looked at this reaction and maximised the atom economy:

oxidising ethanol, or oxidising butane and naphtha (from fossil fuels) bothproduce ethanoic acid but both reactions only have an atom economy of

35%. However if you instead react methanol with carbon monoxide you

get an atom economy of 100%, with no waste: CH3OH + COCH3COOH.

This reaction still had some problems though, because it went really

slowly, unless you performed it at 300C and 700 atmospheres pressure,

with a cobalt catalyst and an iodide co-catalyst. And maintaining theseconditions is hazardous and expensive. A company called Monsanto

therefore did some more work on this and tested new catalysts out. They

realised that to get a catalyst with similar properties they could look in

the same column of the periodic table, and that elements further down

this column might be better because they would participate in the

reaction more. So they tried out rhodium, the next element down from

cobalt, and found that with this catalyst, they could reduce thetemperature to 150-200C and the pressure to 30-60 atmospheres. This

was called the Monsanto process.

But there were still some problems. Rhodium is really expensive (more

than gold!) and sometimes the rhodium and iodide ions formed insoluble

salts such as RhI3, which stops it acting as a catalyst, and contaminates

the products. You can stop this by adding water but then you have to do

more drying, which uses more energy. Also rhodium catalysed unwanted

side reactions (such as CO +H2OCO2+H2). So they tried again with the

next element down in that column of the periodic table, iridium. At first

this did not work as well as a catalyst, but then they discovered that

adding ruthenium as well made a really active and specific catalyst. With

this you avoid all the problems of rhodium but still get to use low

temperatures and pressures, and you dont get so many by-products. This


19/34

process is now called the Cativa processand is illustrated in the diagram

below:

You can see that the catalyst is recovered in the process. Scientists are

still trying to improve efficiency further, however, for instance by

producing the methanol which goes into the reaction from waste

products rather than from oil.

Quick Questions

1. Look at the flow diagram above which illustrates the Cativa process.What steps are taken to:

a. produce a pure productb. reduce costsc. protect the environment? (3 marks)

2. Consider the addition reaction of bromine to propene. Work outthe atom economy of this reaction. (3 marks)

3. List four ways in which the chemical industry can be made moresustainable. (4 marks)


20/34

Green chemistryChecklist

Before you try some exam questions check that you have learnt the

unit:

Students will be assessed on their ability to:

(a)Demonstrate an understanding that the processes in thechemical industry are being reinvented to make them more

sustainable

(greener) by:

(i) changing to renewable resources(ii) finding alternatives to very hazardous chemicals(iii) discovering catalysts for reactions with higher atom

economies, e.g. the development of methods used to

produce ethanoic acid based on catalysts of cobalt, rhodium

and iridium

(iv) making more efficient use of energy, eg the use ofmicrowave energy to heat reactions in the pharmaceutical

industry

(v) reducing waste and preventing pollution of the environment(b)discuss the relative effects of different greenhouse gases as

absorbers of IR and hence on global warming

(c)discuss the difference between anthropogenic and naturalclimate change over hundreds of thousands of years

(d)demonstrate understanding of the terms carbon neutralityand carbon footprint

(e)apply the concept of carbon neutrality to different fuels, suchas petrol, bio-ethanol and hydrogen

(f)discuss and explain, including the mechanisms for thereactions, the science communitys reasons for recommending

that CFCs are no longer used due to their damaging effect on

the ozone layer.


21/34

Exam questions

The following questions are extracted from previous past papers. Questions marked with an asterix

were ones in which the quality of your written English was also assessed. Answers are provided at

the end for reference, but it is highly recommended you attempt the questions on your own before

reading the answers.

January 2009

Q18c. iv.* Explain why fire retardants containing some halogenoalkanes, such as CF2ClBr, are being

phased out.

Suggest a reason why the scientific community still supports the use of fire retardants containing

CF3CHF2. (4)

d. (i) In the Cativa process what effect, if any, would increasing the pressure have on the yield of

ethanoic acid? Justify your answer. (2)

(ii) Suggest TWO reasons why it might be difficult, or undesirable, to produce ethanoic acid in

industry by scaling up the laboratory process. (2)

Q21. Ethanoic acid is used industrially in the manufacture of polymers and glues and also in thefood industry as an acidity regulator.

It can be synthesized in the laboratory by the reaction of ethanol with excess sodium

dichromate(VI) solution, acidified with concentrated sulfuric acid. Ethanol is placed

in a suitable flask along with some anti-bumping beads. The concentrated sulfuric

acid is then added a drop at a time. The sodium dichromate(VI) solution is then added a drop at a

time causing the mixture to boil spontaneously. When the addition of the sodium dichromate(VI)

solution is complete, the mixture is heated under reflux for approximately 15 minutes. Theethanoic acid formed can then be separated from the reaction mixture.

CH3CH2OH CH3COOH

(Conditions: Na2Cr2O7, H2SO4, heat, 1 atm)

Ethanoic acid can be produced industrially by the Cativa process. Methanol, which can be

obtained from wood, is reacted with carbon monoxide in the presence of an iridium catalyst.

CH3OH(g) + CO(g) CH3COOH(g)

(Conditions: Iridium catalyst, 2030 atm, 190C)


22/34

*e. An alternative industrial process for the production of ethanoic acid is the oxidation of butane

using a transition metal catalyst at 150C and 5560 atm.

2C4H10(l) + 5O2(g) 4CH3COOH(aq) + 2H2O(l)

Evaluate the greenness and sustainability of the two industrial processes.

Suggest TWO additional pieces of information that would help you make a more informed decision.

(6)

January 2010

(Source: adapted from an article from the NewScientist.com by Tom Simonite, March 2007)

d. Suggest ONE benefit of using a light activated catalyst for the new process.

(1)

*f. Benzene, which is needed for the new process of breaking down carbon dioxide, can be

made from coal. It is now usually made by catalytic treatment of one fraction of crude oil at

temperatures of around 500C and 20 atmospheres pressure.

Q 20. Fuel from the air?

A new catalyst that can break down carbon dioxide gas could allow us to use carbon from the

atmosphere as a fuel source in a similar way to plants.

Plants break the stable bonds in carbon dioxide during photosynthesis. In the natural process,

the carbon dioxide molecule is initially bonded to nitrogen atoms, making reactive compounds

called carbamates. Carbamates are derivatives of carbamic acid, NH2CO2H. These compounds

can then be broken down, allowing the carbon to be used in the synthesis of other plant products

such as sugars and proteins.

A new catalyst produced by scientists is a graphite-like compound made from flat layers of

carbon and nitrogen atoms arranged in hexagons. Carbon dioxide binds to the catalyst and takes

part in the following reaction, which occurs at 150C and at about three times atmospheric

pressure.

C6H6 + CO2 C6H5OH + CO

benzene phenol

Carbon monoxide can then be used to make liquid fuels such as methanol.

The energy required for photosynthesis comes from light, and experiments are now going on todevelop a light activated catalyst which could break down carbon dioxide in a new process.


23/34

Suggest the benefits and disadvantages of breaking down carbon dioxide using benzene and the

catalyst as described in the passage. You should consider

the energy and resources needed the effects on the atmosphere

whether it is a beneficial method for producing energy compared to directuse of fossil fuels.

(6)

January 2011

Q5. Which of the following is a greenhouse gas?

A Argon

B Nitrogen

C Oxygen

D Water vapour (1)

Q8. Which of the following best defines the meaning of the term anthropogenic change?

It is a change caused by

A nature.

B plants.

C animals.

D humans.

(1)

Q12. Which of the following statements is true?

A CFCs and nitrogen monoxide, NO, are involved in the depletion of the ozone layer.

B CFCs act as catalysts for the depletion of the ozone layer, while nitrogen monoxide, NO, does

not.

C CFCs and ozone are free radicals.

D CFCs and nitrogen monoxide, NO, are decomposed by UV radiation.

(1)

Q16. This question is about some reactions which can be used in the manufacture of hydrogen.

Reaction 1 uses two naturally occurring chemicals, water and natural gas. Steam is reacted withmethane to form carbon monoxide and hydrogen in an equilibrium reaction.

Reaction 1 CH4(g) + H2O(g) CO(g) + 3H2(g) H = +210 kJ mol1

In reaction 2, carbon monoxide and steam are passed over copper at high temperature. This forms

carbon dioxide and hydrogen.

Reaction 2 CO(g) + H2O(g)CO2(g) + H2(g)


24/34

The carbon dioxide formed is removed by passing it through potassium carbonate solution in

reaction 3.

Reaction 3 K2CO3(aq) + CO2(g) + H2O(l)2KHCO3(aq)

The potassium carbonate is regenerated by heating the potassium hydrogencarbonate solution in

reaction 4. The carbon dioxide gas produced is released into the atmosphere.

Reaction 4 2KHCO3(aq)K2CO3(aq) + CO2(g) + H2O(l)

b. (i) Discuss, with reasons, the conditions of temperature and pressure that would favour the

production of hydrogen in reaction 1. You should consider the effect of the conditions on both yield

and rate.

(7)

d. (i) State one economic advantage of reaction 4.(1)

* (ii) Reaction 4contributes to global warming. Identify the substance formed in this reaction which

is likely to be responsible and explain the processes that lead to an increase in global temperatures.

Suggest twoeffects an increase in global temperatures might have on the environment.

(4)


25/34

June 2009

*f. (i) Explain what is meant by a carbon neutral fuel (2)

* (ii) Suggest TWO reasons why these biofuels may not be carbon neutral and describe TWO effects

that large scale production of biofuels may have on society. Which of the three biofuels do you

think is the most sustainable? Justify your choice. (5)

Q23. As levels of fossil fuel resources are getting lower, society is increasingly looking at the use

of biofuels as alternatives to coal, oil and gas. Biofuels are derived from plants and examples

include bioethanol, biodiesel and Miscanthus, a plant more commonly known as elephant grass.

These fuels have the advantage of being renewable and the plants take in carbon dioxide as they

grow.

Bioethanol is produced from crops such as sugar cane or corn. The raw plant material is treated

to produce a sugary solution which is then fermented to produce ethanol, water and carbon

dioxide gas. The ethanol is removed by distillation. The resulting solution contains about 96 %

ethanol. The remaining water has to be removed by absorption using a suitable drying agent so

that the ethanol can burn efficiently. The bioethanol can then be burnt alone or mixed with

petrol in vehicle engines.

Biodiesel is formed by the hydrolysis of vegetable oils using sodium hydroxide

solution, followed by esterification with methanol and a sodium hydroxide catalyst. Biodiesel can

then be used on its own in diesel-engined vehicles or mixed with diesel derived from crude oil.

Plants which are used to produce the vegetable oils include rapeseed in the UK, soya bean in the

USA and palm oil in Asia.

Miscanthus, or elephant grass, is a quick growing, high-yield plant that grows up to four metres in

height. After harvesting, the grass is left to dry and then burnt in power stations designed to run

on solid fuels such as coal. In the United Kingdom, farms that produce elephant grass are

normally situated within 50 miles of such a power station.

In an experiment to simulate the production of bioethanol, a student produced a water/ethanol

mixture by fermentation of sucrose solution using yeast. It was then proposed to separate the

ethanol from water by carrying out a distillation on the mixture. The mixture would then be

dried using a suitable drying agent.


26/34

June 2010

Q15. The use of poly(ethene) packaging has been criticised mainly because:

A the complete combustion of poly(ethene) produces dangerous fumes.

B large amounts of oil are consumed in producing the monomer, ethene.

C poly(ethene) degrades to form toxic products.

D the catalyst used in the polymerization of ethene is expensive.

(1)

c. In the early 1900s, the CFC with the formula CCl 2F2 was identified as a refrigerant which was both

non-flammable and non-toxic.

(i) What does the term CFC stand for? (1)(ii) Suggest ONE use for CFCs other than as a refrigerant. (1)

Q22. Halothane is a colourless and sweet-smelling liquid. It has a boiling temperature of 50C.

Halothane vapour was used as a general anaesthetic in hospitals during the mid to late 20th

Century. Patients inhaled the halothane vapour under medical supervision. However, halothane

was found to have some adverse side-effects and was therefore replaced by other

halogenoalkane anaesthetics.

Halothane has the structure

In an experiment, halothane was heated in a test tube with aqueous silver nitrate

and ethanol, using a water bath. Compound X and bromide ions were formed. The structure of

compound X is shown below.

Compound X

C

Cl

H

F

C F

FBr

C

Cl

H

F

C F

FOH


27/34

* (iii) In the stratosphere, CFCs are broken down by absorption of UV radiation to form chlorine free

radicals.

The following two reactions occur.

Cl

+ O3ClO

+ O2

ClO+ OCl

+ O2

Combine these two equations to give the overall equation for the reaction of ozone in the

stratosphere. State the role played by the chorine free radical in the overall reaction. Hence explain

why many scientists consider the effects of CFCs on ozone to be harmful. (5)

d. The compound of formula CH2F2has replaced several CFCs for commercial use. If molecules of

CH2F2reach the stratosphere, they do not break down to produce fluorine free radicals.

(i) Suggest why C-F bonds are notbroken in the stratosphere. (1)

* (ii) The compound CH2F2acts as a greenhouse gas when it absorbs a particular type of radiation.

Name this type of radiation, and explain why a molecule of CH2F2 is able to absorb this radiation.

(2)


28/34

ANSWERS TO QUICK QUESTIONS

Global warming and climate change

1. There is much more carbon dioxide in the atmosphere than the other gases and therefore

it has a bigger effect. Carbon dioxide is the greenhouse gas most often released by human

activities so we are very interested in its effects and how it might contribute to natural or

anthropogenic climate change.

2. By looking at climate data: natural climate change occurs in cycles and is very slow.

Anthropogenic climate change has happened very quickly and recently.

3. Any of: carbon dioxide, methane, dinitrogen oxide, CFCs (or specific example), water

vapour (2 marks for 3 correct, 1 mark for 2)

b. The Earth emits IR radiation/heat (1 mark) some of which is absorbed by greenhouse

gases (1 mark). The greenhouse gases re-emit IR radiation in all directions including towards

Earth (1 mark)

c. How much radiation one molecule of the gas absorbs (1 mark). How much of the gas

there is in the atmosphere (1 mark).

Carbon neutrality and carbon footprint

1a. Not renewable. Takes thousands of years to form. So not really carbon neutral

b.Feedstock may be renewable and carbon-neutral eg/ biomass, but the industrial process

requires energy, usually not from a carbon neutral source.

c.Carbon emissions here come from production of fertiliser, pesticides and tools for growing

the crops, processing and refining and transporting the crops, infrastructure. So not carbon

nautral.

d. Producing the solar panels takes energy and is probably not carbon neutral. The transport

and infrastructure are probably not carbon neutral.

Pick any of b-d and give a sensible reason. Other considerations: type of application energy

will be used for - eg. biofuel for some cars, solar power for calculators. Efficiency depending

on location eg/ solar power better somewhere more sunny than the UK!

2. a They are unreactive/chemically stable, non-toxic, non-flammable, volatile (3 marks forany 3). Uses: fridge coolants, aerosol propellants, fire extinguishers, foaming plastics (3

marks for any 3)

b.Because they were destroying the ozone layer.

c. CCl2F2 + hv CClF2 + Cl ; Cl + O3ClO + O2 ; ClO + O32O2+ Cl 3 marks for

recognisable equations, 3 marks for balancing and correct notation.

3. Give 2 marks if reasonable reasons given. Eg/ maybe the person trading their carbon

allowance wouldnt actually have emitted anyway (produces false saving). Doesnt promote

development of new green technologies etc. Is unfair because you shouldnt be able to buy

your way out of doing the right thing.


29/34

Reducing hazards and pollution in the chemical industry

1. Plants can be grown quickly and the same field can be used to grow crops everyyear. That means the carbon dioxide released on burning/using the plants can bequickly re-sequestered by growing more crops.

2. Insufficient interest or funding from government or companies, problems with thetechnology (eg gas seeping out again), people may find other solutions, it might be

easier to just lower emissions. (any 2 or reasonable answer)

3. Because this process produces carbon dioxide which is also a greenhouse gas(although it does not cause acid rain).

4. Costs rising, awareness of green issues, reputation of companies, low availability offossil fuels, better alternatives. (any 2 or reasonable alternative answer).

Increasing efficiency in the chemical industry

1. a. Drying column, distillation, separation tank (from catalyst)b. use good catalyst to reduce temperature, recycle catalyst

c. burning waste gases, getting reactants and energy from sustainable source, use

less energy by using lower temperature (catalyst) (Each part, any 1 point =

1 mark)

2. Equation: Br2+ CH3-CH=CH2CH3-CHBr-CH2Br

=

= = = 100%

(1 mark for correct answer, 2 marks for correct working, either as above or by

writing out equation and noting that there is only one product (the desired one) soatom economy must be 100%)

3. Any 4 of: use energy from sustainable energy sources, reduce total energy usage,

reduce waste products (have better atom economy), design better catalysts

(perform reactions at lower temperature), use microwaves, use heat exchangers,

recover catalysts, convert waste gases in flues into less harmful gases. (Or any other

suitable answer).


30/34

Answers to exam questions

January 2009

Q18c. (iv)

Halogenoalkanes such as CF2ClBr can release Cl free radicals

Cl free radicals react with O3

Ozone layer depletes

Leading to greater levels of UV exposure

Greater risk of skin cancer

(Any 3 from above, in context and using correct terminology)

AND

CF3CHF2has strong C-F bonds so does not release F radicals

Q21. d. (i)

Increase yield (1)

As reaction moves to RHS as there are

fewer (gaseous) molecules (1)

(ii) Any two considered suggestions e.g.

Yield of lab process may be lowCost of oxidising agent

Toxicity of oxidising agent

Disposal of Cr3+

Control of temperature/rate in scaled up reaction could be difficult

The lab process has a lower atom economy

Energy costs to separate ethanoic acid from reaction mixture

Lab procedure is a batch process

e. Discussion of four aspects of processes

(e.g four from):

Cativa runs at lower Pressure

Hence less energy required (for compression)

Cativa has 100% atom economy

Methanol in cativa could be obtained from renewable sources

Cativa produces only one product so less separation required

Cativa runs at higher temp so greater energy requirements for heating

Each discussion point may made be made using reverse argument but only awarded once


31/34

plus 2 additional pieces of information

(e.g 2 from):

Life cycle cost of catalysts

Life cycle cost of capital equipment

Yield of reactions

Availability of renewable methanol.

January 2010

Q20. d. No heat energy required / low energy requirement / high temperatures not needed

/sunlight (which is renewable) could be used

Ignore generalisations such as greener,environmentally friendly smaller carbon

footprint cheaper or fossil fuels not used.

f. Score 1 mark up to 6 for each clearly made point:

1. Need energy to make benzene / catalyst/ hydrogen

2. High energy / temperature / pressure needed for the reaction (ALLOW stated T

or P)

3. Fossil fuel (oil or coal) used as source of energy, benzene or hydrogen

4. Hydrogen has to be manufactured5. Hydrogen has to be stored

6. Fossil fuels non-renewable

7. Reduces CO2 in atmosphere / recycles CO2

8. CO2, is a greenhouse gas / causes global warming

9. CO toxic

10. Benzene toxic / carcinogenic

11. 100% atom economy in making methanol

12. Beneficial if phenol useful / not beneficial if phenol a waste product

Ignore generalisations such as greener,smaller carbon footprintor environmentallyfriendly.

January 2011

Q5 = D

Q8 = D

Q12 = A


32/34

Q16. b (i): Any seven from:

1 A higher temperature would increase the yield/favour the forward reaction/produce more

hydrogen (1)

2 (as) the reaction is endothermic (1)

3 Increased temperature would increase the rate/speed of reaction /make the reaction go

faster (1)

4 (as) a greater proportion of /more molecules have sufficient /higher/activation energy

(to react) (1)

5 Decreased pressure increases the yield /favour the forward reaction /produce more

hydrogen(1)

6(as) the forward reaction is favoured withmore (gaseous) molecules /mole (1)

7 Decreased pressure would decrease the rate of reaction (1)

8 (as) collision frequency decreases/lesscollisions (1)

Points may muddle into one another

Reverse statements allowed e.g. lowertemperature decreases yield because reaction isendothermic.

Contradictory statements in each pair lose both marks e.g. lower temperature increases

yield because reaction is endothermic.

d. (i) It regenerates /reforms potassium carbonate/reactant(s) (which reduces the cost of

the process)

OR

potassium carbonate can be re-used

Allow recycles potassium carbonate

(ii) 1 Carbon dioxide / CO2. Allow both water and carbon dioxide (1)

2 Traps longer wavelength radiation / traps radiation / IR emitted (from the earth)

OR Absorbs/traps heat /IR

OR Prevents loss of IR / heat (1)

3,4 Any two from:

Rising sea levels / flooding

Polar ice / ice caps /glacier(s) / glacial / habitat

ice melting

Changing (sea /air) currents, Changing weather patterns /more extreme weather / climatechange (2)

Other acceptable alternatives only if well justified e.g. more malaria because more

breeding areas for mosquitoes. But more malaria /desertification /forest fires alone is

insufficient

Three or more correct answers get 2 marks

Three or more answers, where some are wrong,

are marked 1 mark for each correct answer and1

mark for each incorrect answer e.g.Two correct and one wrong award 1 mark


33/34

Three correct and two wrong award 1 mark etc

One on list and one wrong award 1.

Ignore neutral statements

June 2009

Q23. f. (i) A fuel (derived from a plant) that takes in as much CO2(as it forms/grows) (1)

as is released during its production/combustion/when used (1)

OR

A fuel (such as hydrogen) that produces no CO2when burnt (1)

Nor in its production/processing (1)

(ii)2 specific reasons e.g

energy used to heat/distil (ethanol water mixture after fermentation) may require burninga fuel/energy

energy required to manufacture fertilisers (to grow plants for biofuels in good yield)

energy required to manufacture inseticides (to grow plants for biofuels in good yield)

energy required to transport fuel to the power plant

biofuels less effective at absorbing CO2than (rain)forests/trees

(2)

2 well reasoned effects on society e.g

use of food crops to produce biofuels reduces food supply

(use of land) for biofuels reduces biodiversity use of land to grow biofuels leads to reduced food supply

leads to deforestation/leads to habitat loss

new jobs created to grow crops on new farmland

increased price of car/car service due to engine modifications

less CO2so less global warming

less SO2so less acid rain

less SO2so less respiratory illnesses e.g asthma

(2)

Choice of most sustainable biofuel with appropriate reasoning e.g elephant grass as it requires little/no energy to process before it is burnt

elephant grass grows very quickly

elephant grass is a high yield crop

Any of the fuels can be burnt using existing technology

(1)

June 2010

Q15 = B


34/34

Q22 c (i) Chlorofluorocarbon (Accept ..flouro spelling)

(ii) Any one of the following / a statement equivalent to: aerosol / propellant / spray

cans

OR (degreasing) solvent

OR fire retardant

ALLOW fire extinguishers / putting out fires

ALLOW making expanded polystyrene / making plastics / making polymers

REJECT: pesticides / anaesthetics,just retardant, anti-freeze, air-conditioning, frying pans,

detergents

(iii) Mark independently

1st

mark: O + O3

2O2

IGNORE any state symbols (1)

2nd

mark: (chlorine free radical acts as a) catalyst (1)

Last 3 marks: any three from:

(the chlorine free radical) persists in the atmosphere / continues to attack / is regenerated

/ (starts) a chain reaction (1)

NOTE chain reaction may be described in terms of a chlorine radical breaking down many /

a large number of / a specified number of, eg 10,000, O3

(molecules).

NOTE: As written, this response also earns the scoring point relating to ozone depletion.

less ozone / ozone decreases / causes hole(s) in ozone layer / breakdown of ozone (layer)

/ damages ozone layer / depletes ozone layer (1) UV (reaching Earths surface) increases / less UV absorbed / (more) UV reaches Earths

surface (1)

causes (skin) cancer/mutation / DNA damage occurs (1)

IGNORE any references to global warming / Greenhouse Effect

If Cland / or ClOleft in equation OR 2O3

3O2

Just (UV) harmful

d. (i) The C-F bond is (very) strong

ORC-F bond is (much) harder to break than the C-Cl bond

OR

UV/radiation does not have enough energy /does not have (high) enough frequency

REJECT Any mention of electronegativity OR mention of bond polarity scores

(ii) (long wavelength) IR /infrared radiation (1)

The molecule is polar OR (the molecule) changes its polarity OR polar bonds OR

vibrational energy/vibrations of the bonds / stretching or bending increases OR (IR causes)

bonds to vibrate (1)

Marks are stand aloneC UC/ l i l j l l ib

green chemistry pack 2

Documents