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(C1) OCR 21st Century Science GCSE: Chemistry - Air Quality

The Atmosphere (old, now, future?) - Evidence of atmospheric change - Fuels & Combustion - Complete and Incomplete Combustion - Pollutants & their Impact on the Environment & Health - Improving Air Quality
by

J Amuah-Fuster

on 8 July 2016

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Transcript of (C1) OCR 21st Century Science GCSE: Chemistry - Air Quality

The Atmosphere
Fuels & Combustion
Pollutants
Improving Air Quality
OCR 21st Century:
Chemistry (C1) - Air Quality

How the atmosphere developed and where pollutants come from
and their effects on the atmosphere
Lesson Objectives
C1.1.1 recall that the atmosphere (air) that surrounds the Earth is made up mainly of nitrogen, oxygen and argon, plus small amounts of water vapour, carbon dioxide and other gases

C1.1.2 understand that air is a mixture of different gases consisting of small molecules with large spaces between them

C1.1.3 recall that the relative proportions of the main gases in the atmosphere are approximately 78% nitrogen, 21% oxygen and 1% argon
To know the difference between an
element
,
compound
and
mixture
.

Development of the Earth's Atmosphere
Our modern atmosphere took millions of years to develop
other trace gases include water vapour
From Old to New
Geological
and
biological
activity made it what it is today
How burning fuels affects the environment
Our fossil fuels are
coal
,
oil
and
natural gas
.
Coal is mainly
carbon
.
Oil and natural gas are mainly
hydrocarbons
(made of
carbon
and
hydrogen atoms only
)
Incomplete combustion of methane
When a fuel burns, combustion reactions
oxidise
the carbon and hydrogen into carbon dioxide and water (vapour):
Complete combustion of methane
Methane + Oxygen Carbon dioxide + Water

CH +
2
O CO +
2
H O
Methane + Oxygen Carbon (soot) + Water

CH + O C + 2H O
Further incomplete combustion of methane
What happens when a fuel burns?
Methane + Oxygen Carbon monoxide + Water

2CH + 3O 2CO + 4H O
4
2
2
2
2
4
2
2
4
2
hydrocarbon carbon dioxide
+ +
oxygen water
Oxygen:
Helpful

or

Harmful
?
Not enough oxygen inside car cylinders, so instead of all changing to carbon dioxide, produces carbon monoxide instead.
Incomplete combustion
Hydrocarbons in car engine
Smoke (soot particulates) from
incomplete combustion
are very small pieces of carbon suspended in the air. They can travel with the wind and have significant drawbacks:
Global dimming - reduced light and heat reaching Earth (less photosynthesis and disrupted weather patterns)

Soot sticks to surfaces making buildings dirtier.

Breathing problems may be worsened by particulates in the air.
The acidic gases (sulfur dioxide and nitrogen oxides) escape into the atmosphere and dissolve in the water droplets that form rain clouds.

Once dissolved, the gases become acidic solutions of sulfuric acid and nitric acid.
These 'acid rain' clouds are secondary pollutants, as they are formed in t air by other chemical reactions.
Earth's surface is warmed by the Sun, and then emits infra-red radiation back into space as it cools.

Carbon dioxide absorbs some of this energy.
Increasing levels of carbon dioxide absorb more infra-red radiation.

Less heat escapes, like a 'greenhouse' and the Earth gets warmer.
Combustion Summary
Air is a gaseous
mixture
.

Some are elements, others are compounds.

It contains many different substances (gases) that
can be easily separated
.
Elements, compounds and mixtures
Can you tell which is which?
Elements
are made up of
one type of atom
Compounds
are made up of
more than

one type of atom chemically bonded together
Design a cartoon strip / flow diagram / poster / play / poem / lyrics to describe how Earth's modern atmosphere may have developed from its early atmosphere.
Diatomic oxygen (O ) is a reactive molecule.
It is essential to life on this planet. Using oxygen, organisms can carry out all-important
exothermic
reactions, like
respiration
.
2
Because of this reactivity, given enough energy,
oxygen will react with most substances
.

During this reaction, oxygen reacts to produce
oxides
of the substance.
Diatomic oxygen has further benefits.
with sufficient high concentrations, it can be converted into Ozone (O ). This is an important molecule as it absorbs harmful UV radiation from the sun, reducing damage to our skin, eyes and cells in general.
3
Lesson Outcomes
Draw a graph from secondary data

Carry out calculations using fractions and percentage… (Need to know how to convert mass into percentage by mass) – calculating the percentage of oxygen in the air…
Using the table to the left, calculate the percentages by mass of each constituent of dry air .

Represent this data on a suitable graph
(hint: use a pie or bar chart)
(show working out!!)
Lesson Objectives
C1.4.1 understand that other gases or particulates may be released into the atmosphere by human activity or by natural processes and these can affect air quality
C1.1.5 Understand how the Earth’s atmosphere was probably formed by volcanic activity and consisted mainly of carbon dioxide and water vapour
C1.1.6 Understand that water vapour condensed to from the oceans when the Earth cooled
C1.1.7 Explain how the evolution of photosynthesising organisms added oxygen to and removed carbon dioxide from the atmosphere
C1.1.8 Explain how carbon dioxide was removed from the atmosphere by dissolving in the oceans and then forming sedimentary rocks, and by the formation of fossil fuels.
Lesson Outcomes
Ia S 4.1 scientists report their claims to other scientist through conferences and journals. Scientific claims are only accepted once thy have been evaluated critically by other scientists
Ia S 4.2 Scientists are usually sceptical about claims that cannot by repeated by anyone else and about unexpected findings until they have been replicated
Ia S 4.3 if explanations cannot be deduced from the available data, two scientists may legitimately draw different conclusions about the same data…
Ia S 4.4 an accepted scientific explanation is rarely abandoned just because some new data disagree with its predictions…
Theory
of development

The Oxygen Debate
To answer

1) Look at the illustration of the earliest atmosphere.
a) Which gases are thought to have made up the earliest atmosphere?
b) Where did these gases come from?

2) What happened as the Earth cooled?

3) How did the appearance of photosynthesising plants change atmosphere?

4) Give two ways in which carbon dioxide levels gradually dropped.
Questions to go with the cut and stick
Separate crude oil using fractional distillation
Crude oil separated in a fractionating column
Temperature
decreases going up the column
Crude oil is
separated
into fractions using the
different boiling points
of
different hydrocarbons
.
Crude oil – a
mixture
of many different
hydrocarbons.
These are compounds made up of
only carbon and hydrogen
atoms.
As it is a
mixture
, the molecules in crude oil are
not chemically bonded
, meaning it
can be separated
.
Each hydrocarbon has its own physical properties even though it is in a mixture.
Quick check
Explain the meaning of the word '
hydrocarbon
'.
Explain how you could separate a
mixture
of:
Solid and a liquid.
Two or more liquids with different boiling points.
Balancing combustion equations
Try these...
Step-by-step
Balance carbon first.
Balance hydrogen second.
Calculate the sum of the oxygen in water and carbon dioxide on the right hand side.
Subtract any oxygens in the carbon containing compound on the left (reactant) from your total oxygens on the right.
Divide the new oxygen total by 2 and place this in front of O .
If the coefficient is
not divisible by 2
,
multiply the whole equation by 2
to cancel out the fraction.
2
Pollutant can be formed by natural processes (volcanoes, biological decay and forest fires) or through the activity of humans (power stations, industrial plants and transport).
Lesson Objectives
understand that atmospheric pollutants cannot just disappear, they have to go somewhere:
understand what causes particulates and the effect they have on health and buildings
know sulfur dioxide and nitrogen dioxide react with water and oxygen to produce acid rain which is harmful to the environment
understand that carbon dioxide contributes to global warming but is used by plants for photosynthesis and dissolves in sea and rain water

To be able to process data using mean calculations and range

To be able to use the real difference concept to determine confidence in reaching a conclusion.
Lesson Outcomes
Lesson Objectives
Know what complete and incomplete combustion is and how it can be represented by chemical equations.

Understand how to balance combustion equations.

Know where hydrocarbon fuels are obtained from (fractional distillation)
Lesson Objectives
I know how to write chemical equations for complete and incomplete combustion.

I understand how to balance combustion equations.

I know that fractional distillation provides us with hydrocarbon fuels by separating crude oil.
What can we do to reduce air pollution?
Removal of
sulfur
&
sulfur dioxide
The removal of sulfur from fuel
before burning
and removal of
SO from waste gas
(using '
wet scrubbers
' - alkaline slurry or sea water) can reduce the formation of 'acid rain'.
Preventing
nitrogen oxides
By combusting nitrogen-containing fuel in
low oxygen
conditions, the
nitrogen oxides
are then
reduced

to nitrogen gas
(N ).
Catalytic convertors
Since January 1993, all cars have been fitted with catalytic convertors.
What does this reading tell you?
Improved transport
Energy conservation & cleaner fuels
Reducing demand for heating and electricity reduces the combustion of fuels. This can be achieved by insulating homes and turning off unused lights and power sockets.
Monitoring emissions
In order to achieve set goals, as in the Kyoto Protocol, levels of atmospheric gases need to be measured.
This can be done nationally and locally, by weather stations, or individually using analytical instruments or living pollution indicators, such as lichen.
2
Carbon monoxide
and
nitrogen oxide
react to produce
carbon dioxide

and

nitrogen

gas.

This
reduces the harmfulness
of the pollution.
Emission-free electricity is preferable but has drawbacks
Biofuels
‘Flexi-Fuel’ vehicles, fitted with modified fuel injection systems, can run on E85 fuel (85% bioethanol, 15% petrol), which cuts carbon dioxide emissions by 70% compared to normal petrol-engine cars.
Bioethanol is an alcohol produced by the natural fermentation of the carbohydrates (such as starch) in sugar beet/cane or wheat crops.
What is bioethanol?
Biodiesel can be mixed with conventional diesel, which significantly reduces emissions, especially toxic hydrocarbons, particulates and carbon monoxide.
There are few garages in the UK that sell biodiesel. Home-made fuels, usually from waste vegetable oils, are heavily taxed.
Biodiesel is produced by chemically reacting vegetable oils or animal fats with alcohol and a catalyst. The process can be completed in 12 hours.
What is biodiesel?
By-products of production, such as pressed seedcake, can be burnt in power stations instead of fossil fuels or used as an animal feed
Advantages of biofuels
What are some of the advantages of using biofuels?
Storage, transport and distribution costs are low as biofuels can be handled in the same way as conventional fuels.
Biofuels are carbon neutral: the carbon released during combustion comes from the carbon dioxide the plants took in when they were growing.
The high demand for land to plant biofuel crops can lead to deforestation and habitat loss, for example in Malaysia.
What are some of the disadvantages of using biofuels?
There are few UK producers of biofuels, and only small quantities of fuel are made. Biofuels therefore need to be imported, mainly from Brazil and South-East Asia.
Although biofuels themselves produce relatively little when combusted, their production needs energy from fossil fuels.
Disadvantages of biofuels
Although fossil fuels are convenient sources of energy, they are very polluting, and will one day run out.
As a result, some people have already begun using alternative fuels to power their vehicles, such as biofuels .
Why is it important to develop and use these fuels before oil supplies run out?
Most vehicles in the world use petrol or diesel as a fuel. These are produced from crude oil, a fossil fuel.
The need for alternative fuels
Lots of land is required to grow the sugar beet/cane or wheat crops. This uses up land; either land used for growing food crops, or deforested land (forests cleared to be able to grow crops).
Deforestation
Measuring Pollutants
What's in our atmosphere?
Recall the names, formulae and percentages of the main gases in our atmosphere
For starters...


Explain
– you should process the information given and use your own scientific knowledge/understanding.

Discuss
– you should process the information given and analyse, evaluate or draw a conclusion.

Advise
– this is often a 6 mark question where you need to process some information, use your own scientific knowledge and use this to draw a conclusion or evaluate.
Command words
Long answer question
http://www.bbc.co.uk/schools/gcsebitesize/science/21c_pre_2011/materials/measuringpropertiesrev5.shtml
What's the REAL DIFFERENCE?
Firstly, the real difference means when the ranges for two different values do not overlap. If they do overlap, then there may not be a difference in the true value.

Secondly, if there is a real difference, the range of one value should not overlap the mean of another value.
Amy's chemistry results (%) are in the table.
Calculate the range and mean values for Amy's homework and in-class quizzes.

Is there a
real difference
between her results for each type of assessment?

Amy's final grade is determined as follows:
Homework - 20%
In-class quiz - 50%
Final exam - 30%
What is Amy's final 'weighted' average?
Complete combustion of methane
A closer look...
The chemicals we consider as the main pollutants are formed through oxidation and decomposition reactions occurring at high temperatures.

These high temperatures can be found in the Earth's mantle (gases released during volcanic eruptions), industrial furnaces (used by industry and power plants), and internal combustion engines (vehicles).
I understand that atmospheric pollutants;
that cause particulates have an effect on health and buildings

like sulfur dioxide and nitrogen dioxide, react with water and oxygen to produce acid rain which is harmful to the environment

like carbon dioxide, contribute to global warming but can be used by plants for photosynthesis and dissolve in sea and rain water

I can process data using mean calculations and range

I can determine confidence in reaching a conclusion by analysing the 'real difference' between data.
Biodiesel in the UK
Converting parts per million (ppm) into percentage (%)
Multiply answer by 100 to change it into a percentage
This gives you a
proportion
out of 1
Take the
ppm
value
Divide
by 1,000,000
How do we know what the air was like in the past..?
Deep ice in the Arctic and Antarctic has remained on the Earth for millions of years
The
deeper
the ice, the
older
it is.
Scientists use records of snowfall and ice formation to predict the age of ice sections.
Under controlled conditions, the ice columns are sliced into thin sections and ordered according to age.
The ice contains atmospheric gases that had dissolved in the water that eventually formed the ice or snow.
Using this data, we can predict what the Earth's atmosphere was like millions of years ago
Some scientists travel to these locations and use bore drills to extract columns of deeply buried ice
Homework
Be Creative
For example,when combusting fossil fuels, Sulfur in the fuel and nitrogen from the air react with oxygen in the air (at high temperatures) to produce
sulfur dioxide
&
nitrogen oxides
.
These are atmospheric pollutants and we will look at these later on.
Provide a mechanism (scientific explanation) for how vehicles produce nitrogen oxides
Points to include
David could
collect additional data
about nitrogen oxide pollution from
various locations
Compare
the amount of
traffic
with the
amount of pollution
measured
-
at
high temperatures
found in an engine
- nitrogen and oxygen from air react
together to form nitrogen oxides
- nitrogen oxide in the air reacts with oxygen
in atmosphere to make nitrogen dioxide
Friday
6-Mark Q
Correlation
To be able to explain when there is a correlation between a factor and an outcome

To be able to decide whether there is a cause for a correlation between a factor and outcome
Lesson Outcomes
Time spent in the sun = more sunburn
A link between two variables, when one variable
directly causes
a change in the other.
Causal Link
Playing darts does not cause obesity
A link between two variables, when one variable does
not directly cause
a change in the other.
Non-Causal Link
Think of two correlating variables which have a causal link?
Can you...
Chose one of the graphs and
explain the cause
for the correlation
Washing hands and less infection.
Washing hands and being intelligent.
Switching on the kettle and boiling water.
Switching on the kettle and the adverts coming on.
Smiling at someone and them smiling back.
Driving above 30mph and pedestrian death.
Amount eaten and body weight.
Bank Holidays and traffic jams.
Rainfall and flooding.
Causal Link ? Yes or No
Think of two correlating variables which don’t have a causal link?
What trends do these graphs show us?
Is there a correlation?
Can you suggest why this trend is observed?
Causal & Non-Causal Links
When do hayfever symptoms appear?
1995
1994
1993
1992
1991
Describe any pattern that you can see in the data.

Why do you think the statistics only include people who were 'known' sufferers from hay fever?

Why do the figures show '
prescriptions per thousand of population
' rather than just showing the total number of prescriptions?
Questions to consider
Graph shows a
slight
increased incidence
of
hay fever prescriptions
(per 1000 of population)
during March
and a
much larger peak around June/July
, with
lower incidence
of reported symptoms
during the winter
.

Data only counts patients known to suffer from hayfever (diagnosed by GP). This helps to avoid including data where the medicine was given for a cold or other breathing related condition.

It is more useful for
comparing
statistics for

different places

equally
(e.g. comparing a large city with a small town).
Answers
On an acetate sheet (or graph paper), draw line graphs of the information (use a key to distinguish the graphs)
vs

Causation
Positive correlation
showing as the

days increase
,

the
temperature

also

increases
Positive correlation
showing as the

months increase
,

Sam's
weight

also

increases
Negative correlation
showing as the

years increase
,

the
value

of Sarah's car

decreases
A correlation
showing how the

number of people

in a store changes with
time of day
.
Do the values increase and decrease at the expected times? Why?
Car is getting older
Parts getting worn out
Bumps & scratches
Sam is growing up
Sam's eating more food
Sam's body-building
Asthma vs. Traffic pollution
Lesson Outcomes
give an example of a correlation in which a factor increases the chance of an outcome

explain why it is difficult to be sure there is a causal link between traffic pollution and the development of asthma in children
2
Alternatively, nitrogen oxides can be '
scrubbed
' using ammonia and water to produce nitrogen gas and water.
cleaned gases to chimney
water
air
waste gases from furnace
ammonia and water
Exhaust gases
in the catalytic converter
pass over

metals
, arranged with a
large surface area
.
Lighter
,
more aerodynamic
vehicles can also
reduce fuel consumption
, and therefore emissions.
Transporting more people
at once (carpool, buses, trains, trams) or
using cleaner technology
(bicycles, electric vehicles, or foot!) can
reduce local emissions
greatly.
Removing
particulates
Particulates
produced by different process, e.g. soot (carbon formed through incomplete combustion), can be
removed
from waste gases
before

entering the air
.
They then have to pass by
positively-charged
collecting plates which
attract
them before they leave the chimney.
To do this, the particulates are passed through a negatively-charged metal grid that
makes them negatively-charged
.
Many car journeys are for
less than a couple of miles
and usually involve
one person
.

The engine is cold at the start and works less efficiently. This gives a
high
fuel:distance ratio

per person
.
Some ways...
How can we
reduce
this ratio?
MOT tests
are compulsory.
Part of the test is to check the
vehicle's exhaust gases
.
If the emissions are within the
legal limit
set by the government, the vehicle may pass.
Full transcript