Topic 1: Monitoring the Environment

Question 1

Why is most solar radiation reaching the Earth reflected?

Answer 1

Thanks to the albedo, reflectivity, of its surface from sources such as ice, snow, and clouds

Question 2

After solar radiation makes its way into the atmosphere, what happens to it?

Answer 2

It is absorbed by the Earth’s surface (buildings, trees, etc.). Some is retained as heat whilst the rest is reradiated as thermal infrared radiation
(This energy is polarised, travelling in 2 dimensions)
Most passes through the atmosphere and into space, but some is absorbed by molecules in the atmosphere, greenhouse gases, trapping some of the heat in the atmosphere before reradiating the thermal radiation into other molecules, space, or back to the Earth’s surface

Question 3

Greenhouse gases come from organic and synthetic sources. Name six. What do they share in common?

Answer 3

Water vapour (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and sulfur hexafluoride (SF6)
They are have polar covalent bonds

Question 4

What are anthropogenic influences, and how do they change concentrations of greenhouse gases?

Answer 4

They are human influences, and have recently added to concentrations of naturally occurring greenhouse gases whilst also introducing synthetic ones

Question 5

Natural source of water in the atmosphere?

Answer 5

Present in the atmosphere as water vapour and clouds, moving between soil, bodies of water, and the atmosphere via the water cycle

Question 6

Natural source of carbon dioxide?

Answer 6

Released during aerobic respiration, aerobic decomposition of organic matter, the combustion of natural vegetation, and volcanic activity

Question 7

Natural source of methane?

Answer 7

Released during the anaerobic decomposition of organic matter in soil. Also released when sea ice melts

Question 8

Natural source of nitrous oxide?

Answer 8

Formed through denitrification (reduction of nitrate ions) in natural vegetation in soil and oceans

Question 9

Natural source of ozone?

Answer 9

Occurs naturally in the stratosphere. Created and destroyed through the absorption of UV radiation in photochemical reactions

Question 10

Describe Earth’s thermal balance and how it is maintained at its current level

Answer 10

The temperature of the Earth is maintained thanks to greenhouse gases
For thousands of years, the temperature of the Earth’s atmosphere has been in thermal balance: the ratio of energy being absorbed and reradiated into space by the Earth has remained the same

Question 11

How is global warming caused?

Answer 11

Greenhouse gas concentrations have risen due to anthropogenic activities, resulting in less thermal radiation escaping the Earth, generating a thermal imbalance (more energy being retained in the atmosphere), increasing temperature

Question 12

Provide an example of a global feedback mechanism that has driven further increase in global temperature

Answer 12

More water vapour is now present in the atmosphere due to greater evaporation, which in turn absorbs more energy while acting as a greenhouse gas, further increasing atmospheric temperature
or talk about ice melting reduces albedo, further increasing thermal IR radiation, further increasing temp., or whatever

Question 13

How does melting ice affect climate change?

Answer 13

Melting ice causes sea levels to rise, and the fresh water alters temperature and salinity, affecting ocean currents, which impact weather patterns and hence climate
The melting ice and snow also reduces Earth’s albedo, resulting in decreased reflected solar radiation and increased global temperatures

Question 14

As global warming continues, changes have occurred in the frequency and severity of weather events. How have these affected the Earth?

Answer 14

Such events impede global crop production and can impact natural vegetation and animal species, putting them at risk of extinction, which can permanently change biodiversity in ecosystems

Question 15

How has the ocean helped mask the enhanced greenhouse effect?

Answer 15

Thanks to its high specific heat capacity, the water of the ocean can absorb the increased energy, masking the enhanced greenhouse effect

Question 16

How has urbanisation affected global warming? Aside from carbon dioxide emissions etc.

Answer 16

Urbanisation has led to more buildings, which increases the surface area for heat to be absorbed and subsequently reradiated etc.

Question 17

What are some natural sources of energy that can cause nitrogen (N2) to react?

Answer 17

Lightning, volcanic activity, bushfires

Question 18

What are some anthropogenic sources of energy that can cause nitrogen (N2) to react?

Answer 18

Internal combustion engines, jet engines, industrial kilns & furnaces

Question 19

High temperatures from various sources can break the bonds of nitrogen and oxygen molecules, which react to form what?

Answer 19

N2 + O2 -> 2NO
nitrogen + oxygen -> nitric oxide
It’s oxidised
(nitrogen fixation is when the bonds are broken, not when NO is formed)

Question 20

After nitric oxide is formed when bonds of nitrogen and oxygen molecules are broken, what does it react with?

Answer 20

2NO + O2 -> 2NO2
Nitric oxide + oxygen -> nitrogen dioxide
It’s further oxidised

Question 21

What is a pollutant?

Answer 21

A substance present in higher-than-normal concentration and causes harm (injuries to life, economic loss, social disruption)

Question 22

What are the two main sources of pollutants?

Answer 22

Can be from:
Primary sources - direct emissions e.g. carbon dioxide from cars
Secondary sources - formed in atmosphere e.g. ozone in photochemical smog

Question 23

What is photochemical smog?

Answer 23

A mixture of pollutants that exist in the atmosphere

Question 24

What are the necessary conditions required for the formation of photochemical smog?

Answer 24

High concentration of pollutants
Sunlight - many reactions in its formation are initiated by the absorption of UV radiation and heat
Still air masses - prevents pollution from being dispersed or displaced
Temperature inversion - pollutants tend to move from warm air to cool air. Having a layer of warm air above a layer of cool air means the pollutants won’t move up

Question 25

What are two main components of photochemical smog?

Answer 25

Ozone and nitrogen dioxide, the latter gives it a brown haze

Question 26

Describe the formation of photochemical smog

Answer 26

Combustion of fuel in internal combustion engine provides energy needed to initiate the reaction of nitrogen (N2) and oxygen (O2) to form nitric oxide (NO), a primary pollutant
Nitric oxide is then oxidised during or after exhaust is emitted, forming nitrogen dioxide (NO2), a secondary pollutant
Then nitrogen dioxide photodissociates in the presence of UV radiation to form nitric oxide and a highly reactive oxygen radical (O)
The oxygen rapidly combines with an oxygen molecule to form ground level (tropospheric) ozone (O3), a secondary pollutant

Question 27

State the equations of the chemical reactions involved in the formation of photochemical smog

Answer 27

N2(g) + O2(g) -> 2NO(g)
2NO(g) + O2(g) -> 2NO2(g)
NO2(g) UV-> NO(g) + O(g)
O(g) + O2(g) -> O3(g)

Question 28

What can photochemical smog have effects on?

Answer 28

Can have detrimental effects on humans, animals, plants, and synthetic materials (including some polymers)

Question 29

How can exposure to photochemical smog affect humans and animals?

Answer 29

Pollutants in smog react with the fluid secreted to lubricate the eyes, making it more acidic, causing eye irritation
Pollutants in smog also irritate and damage tissues lining the lungs when inhaled, reducing the rate of diffusion of oxygen to the lungs over time

Question 30

How can exposure to photochemical smog affect plants and vegetation?

Answer 30

During photosynthesis, gases enter stomata (gas-exchange pores) on the surface of the leaves, including ozone from smog
Exposure to high levels of ozone cause stomata to close, limiting the exchange of gases required for photosynthesis
Ozone entering a plant also undergoes various reactions, further disrupting photosynthesis and other cell reactions
Results in limited plant growth and susceptibility to disease and extreme weather conditions

Question 31

How can exposure to photochemical smog affect polymers?

Answer 31

Ozone can damage elastomers (elastic polymers) by cleaving polymer chains where carbon-carbon double bonds exist, oxidising them
This makes these materials more brittle and susceptible to cracking under stress

Question 32

What is the role of a catalytic converter in an exhaust system?

Answer 32

To reduce the impact of pollutants released as exhaust emissions by converting a number of precursor compounds of photochemical smog to less harmful products

Question 33

Describe the structure of a typical three-way catalytic converter

Answer 33

Consists of a porous ceramic block with parallel channels along it to allow exhaust emissions to flow
Coated with a thin layer of highly porous alumina (aluminum oxide), with very small amounts of the precious platinum-group metals bonded to the surface in the alumina coating

Question 34

How do typical three-way catalytic converters work?

Answer 34

The channels and porous alumina mean more surface area for hot exhaust gases passing through to contact the metal catalysts, increasing the rate of reaction
The metals catalyse redox reactions to remove carbon monoxide, nitrogen oxide, and unburnt hydrocarbon components of the fuel

Question 35

How does a catalytic converter convert nitric oxide?

Answer 35

Nitric oxide can be removed by reduction with carbon monoxide, catalysed by the metals
2NO(g) + 2CO(g) -> 2CO2(g) + N2(g)

Question 36

The oceans and natural bodies of water absorb much of the carbon produced by anthropogenic activities. It then increases the acidity of the ocean. State the steps on how this occurs.

Answer 36

Carbon dioxide is soluble in the sea and reacts to form carbonic acid
CO2(g) + H2O(l) <->H2CO3(aq)
Carbonic acid is weak and partially ionises, forming hydronium and bicarbonate ions
H2CO3(aq) + H2O(l) <-> H3O+(aq) + HCO3 -(aq)
Bicarbonate ions further ionise to form carbonate ions
HCO3 -(aq)+ H2O(l) <-> H3O +(aq) + CO3 2-(aq)
Increased hydronium concentration results in decreased pH of the oceans

Question 37

Formula for calculating pH?

Answer 37

pH = -log[H3O +]

Question 38

What happens to shells of marine creatures when pH decreases?

Answer 38

Lower pH means more H+ ions, increasing the reaction of CaCO3 + 2H+ -> H2O + CO2 + Ca2+, resulting in marine creatures’ shells dissolving as they are made of calcium carbonate and making it harder to build new shells due to less available calcium carbonate.

Question 39

State the equation of calcium carbonate reacting with sulfuric acid. The ionic equation too. (An example of carbonates being dissolved by acids)

Answer 39

CaCO3 (s) + H2SO4 (aq) -> H2O (l) + CO2 (g) + CaSO4 (aq)
CaCO3 (s) + 2H +(aq) -> CO2 (g) + Ca 2+(aq)

Question 40

Compare the level of pollutants in photochemical smog in the morning, at midday, and in the evening

Answer 40

In the morning there would be a high concentration of primary pollutants due to peak hour traffic (NO), but due to little sunlight, concentration of secondary pollutants that are generated through photochemical reactions would be low (O3)
At midday, primary pollutants would be turning into secondary pollutants thanks to high UV levels
In the evening, peak hour traffic would again increase concentration of primary pollutants, but there is less UV to form secondary pollutants

Question 41

Describe the preparation and use of a volumetric pipette.

Answer 41

Ensure it is free from defects
Clean it: rinse it with distilled water taken up by a pump several times, running it over all surfaces by holding it horizontally. Rinse it also with a small volume of the solution being delivered.
When using it, lower the pipette into the solution to avoid the generation of air bubbles.
Carefully draw in or release solution until the bottom of the meniscus meets the calibration line
When transferring the solution, touch the tip of the pipette to the flask in order to avoid splashing and ensure the full volume is transferred

Question 42

Describe the preparation and use of a burette for a titration

Answer 42

Ensure it is free from defects
Clean it: pour in distilled water through a clean funnel and run it over all surfaces by holding it horizontally, and then pouring it out through the tap. Do so several times before doing the same with a small volume of the solution to be delivered
The burette is then filled using a clean funnel, and a small volume of the solution is run through the tap to remove any air bubbles
When titrating, the sides of the conical flask are periodically washed to ensure all reactants are present in the solution
“The equivalence point is established when the mole ratio of reacting quantities is met. the endpoint is recognised as a permanent observable change past the equivalence point (point where the stochiometric ratio has been achieved)”

Question 43

For how long are titrations typically repeated?

Answer 43

Until three concordant titres are obtained
Concordance is obtained when the titres are within +-0.05

Question 44

Explain the purpose and main things used in chromatography

Answer 44

A technique used to separate and identify components of a mixture
Involves the use of:
A sample (whose components are being separated)
A stationary phase (usually solid, which the parts of the sample are adsorbed to at different strengths)
A mobile phase (a fluid which drives the separation)
Chromatography relies on the differing polarity of substances to separate them

Question 45

Explain thin-layer chromatography

Answer 45

Uses a thin surface as a stationary phase - usually a thin layer of adsorbent material is bonded to the surface of an inert sheet of material (glass, aluminum)
The sample is dropped onto a point on the stationary phase, marked with a line (the origin)
The stationary phase is lowered into a beaker containing a liquid mobile phase, sitting just below the origin
Due to capillary action, the mobile phase moves up, taking up components of the sample at different rates due to different levels of adsorption to the stationary phase, separating them
The plate is removed before the solvent front reaches the top of the plate, producing a chromatogram

Question 46

What is the retardation factor, what does it measure, and how do you calculate it?

Answer 46

It is a ratio that indicates how far a component of a sample has travelled compared to the distance the mobile phase has travelled
Rf = dist. travelled by component (from origin)/dist. travelled by mobile phase
An Rf value closer to 1 indicates the component has travelled close to the solvent front, whilst a value closer to 0.1 indicates the component remained close to the origin

Question 47

Explain column chromatography

Answer 47

A form of liquid chromatography that uses a column which is packed with a stationary phase
A solvent mobile phase (the eluent) containing the sample is poured into the top of the column, flowing down due to gravity
The components will travel at different rates due to varying levels of adsorption to the stationary phase, resulting in bands that elute the column one at a time

Question 48

Explain gas (liquid) chromatography

Answer 48

For separating components of gaseous samples
Uses a long, coiled chromatography column in an oven that ensures the sample remains gaseous
The mobile phase is an inert carrier gas (hydrogen, nitrogen, helium), which transports the sample through the column
There are two main types of stationary phase:
Capillary columns where the stationary phase is coated onto the surface of the column - it melts due to the heat into an absorbed liquid
Packed columns - the column is completely packed with the stationary phase
Components that are more strongly adsorbed to the stationary phase are retained for longer, whilst those that are less adsorbed elute more quickly
(Long column makes process more energy and time consuming, but higher resolution can be achieved)

Question 49

How do you read quantitative chromatograms?

Answer 49

The x-axis is retention time - the time taken from the sample’s injection to elution
The y-axis is relative abundance/concentration
Retention times can be compared with known standards under the same conditions to identify components
(Lower retention time means the component was less adsorbed to the stationary phase)

Question 50

Explain high-performance/pressure liquid chromatography

Answer 50

Uses a column packed with a stationary phase made up of small particles (hence large surface area)
The eluent (liquid mobile phase) must be pumped through under high pressure and at a constant flow rate, carrying the dissolved gas sample
Components that are more strongly adsorbed to the stationary phase are retained for longer, which is measured by a detector

Question 51

What are the benefits and negatives to gas chromatography and HPLC?

Answer 51

Both have long columns that allow for higher resolution, but are time consuming.
Gas chromatography’s oven also requires a large amount of energy
HPLC is good for samples that may break down at high temperatures in the oven of gas chromatography

Question 52

Explain the setup and process of atomic absorption spectroscopy

Answer 52

A cathode lamp containing one element is used to create an incident beam, which provides a reading for the initial light intensity
A nebuliser system then draws up the sample and sprays it into a flame
The heat from the flame breaks down the components of the sample and excites their electrons
The beam that passes through this flame, the transmitted beam, is of lower energy as some wavelengths would’ve been absorbed by atoms in the sample
A monochromator separates the transmitted beam into individual wavelengths, of which one is selected for detection, which is unique to the element under investigation

Question 53

How does atomic absorption spectroscopy help identify and determine the concentration of substances?

Answer 53

The detector of the apparatus measures the intensity of the wavelength being detected to determine how much of it has been absorbed by atoms in the flame, which can be used to identify and determine the concentration of an element
Calibration graphs are constructed using standard solutions of the element of interest to interpolate the connection of the element in the sample
A blank is initially conducted with no sample (just distilled water), to calibrate the apparatus
Then, solutions of increasing concentration are added, which register absorbance readings which are plotted onto a calibration graph with a line of best fit
The unknown sample is then added and its absorbance is interpolated with the data to determine the associated concentration

Question 54

Communication & Collaboration

Answer 54

Science is a global enterprise that relies on clear communication, international conventions, and review and verification of results
Collaboration between scientists, governments, and other agencies is often required in scientific research and enterprise

Question 55

Development

Answer 55

Development of complex scientific models and/or theories often requires a wide range of evidence from many sources and across disciplines
New technologies improve the efficiency of scientific procedures and data collection and analysis. This can reveal new evidence that may modify or replace models, theories, and processes

Question 56

Influence

Answer 56

Advances in scientific understanding in one field can influence and be influenced by other areas of science, technology, engineering, and mathematics
The acceptance and use of scientific knowledge can be influenced by social, economic, cultural, and ethical considerations

Question 57

Application and Limitation

Answer 57

Scientific knowledge, understanding, and inquiry can enable scientists to develop solutions, make discoveries, design action for sustainability, evaluate economic, social, cultural, and environmental impacts, offer valid explanations, and make reliable predictions
The use of scientific knowledge may have beneficial or unexpected consequences; this requires monitoring, assessment, and evaluation of risk and provides opportunities for innovation
Science informs public debate and is in turn influenced by public debate; at times, there may be complex, unanticipated variables or insufficient data that may limit possible conclusions