Environmental Chemistry

Question 1

What iss the ‘greenhouse effect’ of greenhouse gases dependent on? (2)

Answer 1

It’s atmospheric concentration and its ability to absorb infrared radiation

Question 2

What is a greenhouse gas? e.g.?

Answer 2

Greenhouse gases have bonds that absorb in the infrared region of the electromagnetic spectrum. E.g. water vapour, methane, carbon dioxide

Question 3

Why is CO2 a major contributor to global warming?

Answer 3

Because the absorbance of infrared by the C=O bonds is high and a lot is produced by burning fossil fuels

Question 4

What are some methods of Carbon Capture and Storage?

Answer 4

Storage of CO2 in oceans, porous rock, as a liquid in geological formations, or by reacting it with metal oxides to form metal carbonates

Question 5

Equation for the formation of ozone?

Answer 5

O2 + O. O3

Question 6

How is ozone maintained at constant levels in the stratosphere?

Answer 6

Made by the reaction of oxygen gas with oxygen free radicals produced by the breakdown of oxygen by UV light found in the stratosphere.
O2 + O. O3
An equilibrium is reached in which ozone is continuously made and broken down

Question 7

What are ways in which the steady concentration of ozone can be affected?

Answer 7

the presence of free radicals such as Cl. from CFCs and NO. from aeroplane exhausts.

Question 8

Describe using equations the effect of CFCs on the ozone layer. Overall equation?

Answer 8

CFCs break down in the stratosphere to produce chlorine free radicals which initiate the following reactions :

Cl. + O3 –> ClO. + O2
ClO. + O –> Cl. + O2

Overall: O3 + O –> 2O2

Question 9

What is the reaction that occurs in catalytic converters?

Answer 9

2CO + 2NO –> 2CO2 + N2

Question 10

Why is it important that CO and nitrogen oxides are converted to less harmful products in a catalytic converter?
/
what are the effects of the chemicals formed in the internal combustion engine?

Answer 10

CO - toxic, binds to haemoglobin preventing it from carrying oxygen - can lead to fainting/death.
NO - respiratory irritant, affects asthmatics even at low levels.
NO2 - contributes to the formation of low level ozone (breathing difficulties, increased susceptibility to infection) and is converted to nitric acid in the atmosphere which contributes to acid rain
these as well as unburnt hydrocarbons formed in the internal combustion engine also contribute to photochemical smog.

Question 11

Describe how a catalytic converter functions. What kind of catalyst does this represent?

Answer 11

1. CO and NO gas molecules diffuse over the surface of the rhodium, palladium and platinum coated honeycomb mesh. Some of them are held on to the metal surface by adsorption.
2. Temporary bonds form between the catalytic surface and the gas molecules, holding them closer together for a reaction to occur.
3. Once reacted, the CO2 and N2 products are desorbed from the surface and diffuse away.

The catalyst is an example of a heterogenous catalyst (of a different phase to the reactants it helps react)

Question 12

outline the role of chemists in minimising environmental damage from polymer usage/disposal

Answer 12

• removal of toxic waste products, ie removal of HCl formed during combustion of halogenated plastics (ie PVC) by neutralising it with an alkali/ensuring incomplete combustion does not occur and produce CO by ventilating the area well.
• development of biodegradable and compostable polymers, ie from isoprene (2- methyl-1,3-butadiene), maize and starch
• sorting and recycling plastics

Question 13

outline the processing of waste polymers (e.g how can they be used when thrown away)

Answer 13

1. separation into types (ie PTFE, etc.) and recycling,
2. combustion for energy production
3. use as a feedstock for cracking in the production of plastics and other chemicals;

Question 14

why were CFCs developed as aerosols, refrigerants and in air-conditioning? why are appliances containing CFCs no longer manufactured?

Answer 14

because of their low reactivity, volatility and non-toxicity
They have caused environmental damage to the ozone layer so international action has been taken to phase out and stop production of appliances containing CFCs

Question 15

What alternatives to CFCs have green chemists developed to replace them and minimise damage to the environment?

Answer 15

biodegradable alternatives e.g. hydrocarbons and HCFCs and CO2 as a blowing agent for expanded polymers

Question 16

outline some uses of mass spectrometry

Answer 16

• identify unknown compounds
• determine abundance of each isotope in a compound- relative isotopic
  masses
• gain further info about the structure and chemical properties of molecules
• as a method for identifying elements, ie use in the Mars space probe and in monitoring levels of environmental pollution, e.g. by lead;
• monitoring the breath of patients during surgery whilst under anaesthetics
• detecting traces of toxic chemicals in contaminated marine life to prove human contribution to pollution

Question 17

How to greenhouse gases CO2, H2O and CH4 contribute to global warming?

Answer 17

infrared radiation is absorbed by C=O, O–H and C–H bonds in H2O, CO2 and CH4 and these absorptions contribute to global warming

Question 18

what is the role of chemists in minimising climate change resulting from global warming?

Answer 18

1. providing scientific evidence to governments to verify that global warming is taking place,
2. investigating solutions to environmental problems, such as carbon capture and storage, CCS, ie the removal of waste carbon dioxide as a liquid injected deep in the oceans, storage in deep geological formations/by reaction with metal oxides to form stable carbonate minerals,
3. monitoring progress against initiatives, such as the Kyoto protocol

Question 19

how is the presence of ozone important to living organisms?

Answer 19

absorbs harmful UV radiation preventing too much from reaching the Earth’s atmosphere and causing sun burn/skin cancer to humans

Question 20

mechanism for the effect of nitrogen oxide radicals on the ozone layer?

Answer 20

NO. + O3 –> NO2. + O2
NO2. + O –> NO. + O2
overall: O3 + O –> 2O2

Question 21

how is nitrogen oxide, NO., which contributes to ozone depletion, released into the stratosphere?

Answer 21

from lightning/aircraft engines

Question 22

outline the uses of infrared spectroscopy?

Answer 22

• monitoring the degree of unsaturation in polymers
• quality control in perfume manufacture
• drug analysis in forensic science
• monitoring air pollution

Question 23

describe the 5 key principles of chemical sustainability

Answer 23

1. using industrial processes that reduce/eliminate hazardous chemicals and
   use fewer chemicals,
2. designing processes with a high atom economy that minimise waste
3. using renewable resources such as plant-based substances as well as renewable sources of energy e.g. solar rather than consuming finite resources e.g. fossil fuels
4. ensuring that any waste products produced are non-toxic and biodegradable
5. use of catalysts that reduce consumption of finite energy sources and increase atom economy

Question 24

how might the apparent benefits of using renewable resources may be offset by unexpected and detrimental side- effects

Answer 24

Production of biodiesel uses grain crops and land needed for food, with poorer countries being worse affected

Question 25

explain the importance of establishing international cooperation to promote the reduction of pollution levels

Answer 25

• we all produce pollution
• pollution produced by one country may affect another - not contained by borders - e.g. in the sea/air
• united international scientists working together to find solutions will get there faster

Question 26

how do modern breathalysers work

Answer 26

measure ethanol in the breath by analysis using infrared spectroscopy