Transcript Evolution and the Environment

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C3 Chemicals in our Lives
– Risks and Benefits
(OCR 21st Century)
W Richards
The Weald School
C3.1 – The origins of Minerals
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The Structure of the Earth
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A thin crust 10-100km thick
A mantle – has the
properties of a solid
but it can also flow
A core – made of
molten nickel and iron.
Outer part is liquid
and inner part is solid
The average density of the Earth is much higher than
the crust, so the inner core must be very dense
Movement of the Lithosphere
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The Earth’s LITHOSPHERE (i.e. the _______) is split
up into different sections called ________ plates:
These plates are moving apart from each other a
few centimetres every _______ due to the
________ currents in the mantle caused by the
________ decay of rocks inside the core.
Words – radioactive, crust, convection, tectonic, year
Plate Movements
Earthquakes and
volcanic eruptions can
be common here
Igneous Rock
Oceanic Crust
Mantle
Convection
Currents
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Magma
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Magnetic Patterns in Sea Floor Spreading
The Earth’s magnetic field swaps poles every million years.
The above picture shows those changes recorded over time in
rocks on the sea floor and provides evidence for long-term sea
floor spreading.
Continental Drift
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Look at the coastlines of South
America and Africa. I wonder of they
used to fit together…
Alfred
Wegener
I’m going to call this my
Theory of Continental Drift
Tectonic theory
Because of this movement, a lot of the rocks
that are in the UK would have originally
formed in different climates. Fascinating!
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What are rocks?
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Rocks are made from a combination of minerals and can be
hard or soft depending on how the minerals are arranged.
Rocks can be
found here…
…and here…
…and here…
…and here
Forming rocks
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Rocks can be broken off the
side of mountains
When rocks are
transported by
a river they are
eroded:
Rock shape up here
Rock shape down here
“Sediment”
Sedimentary rocks and salt
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Processes like mountain building
followed by erosion and sedimentation
have led to the formation of valuable
resources in the UK, like sedimentary
rocks and salt:
Where deposits of such natural
resources were large, chemical
industries quickly appeared, for
example, this coal mine in Yorkshire:
Limestone
Rock salt
Studying Sedimentary Rocks
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Scientists study sedimentary rocks
to get useful information about the
Earth, such as:
This rock contains fossils,
giving useful clues about
the development of life
This rock contains ripple
marks to show where water
was present in the past
This rock contains shells and
other fragments of life
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C3.2 – Where does Salt come from?
Salt
Salt is an important substance for many reasons…
Flavouring and
preservation
Treating icy
roads
Chemical uses
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Ways to get Salt
Salt mines – large scale
underground mining will
produce salt with
impurities so its useful
for roads but not food.
This approach has a rish
of mines collapsing or
causing subsidence.
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Water solutions – a
solution of salty water
(like seawater) can be
left so that the water
evaporates and the salt
crystallizes. This will
produce purer salt.
Government Departments
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Government departments such as the Department of Health
and the Department for Environment, Food and Rural Affairs
have a role in food and health, including carrying out risk
assessments on foods and advising the public on healthy
eating.
A lot of statistics point to a link
between salt and conditions such as
high blood pressure and heart disease.
C3.3 Why do we need chemicals
like alkalis and chlorine?
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Alkalis
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Alkalis are chemicals that have been used for centuries. Some
examples:
Other uses included making glass and binding dyes to cloth.
Alkalis were made from burnt wood or from stale urine!!
Neutralisation reactions
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A neutralisation reaction occurs when an acid reacts with an alkali. An
alkali is a metal carbonate or metal hydroxide dissolved in water.
ACID + ALKALI
Na
O
H
H
Cl
SALT + WATER
Cl
Na
Copy and complete the following reactions:
1) Sodium hydroxide + hydrochloric acid
2) Calcium hydroxide + hydrochloric acid
3) Sodium hydroxide + sulphuric acid
4) Magnesium hydroxide + sulphuric acid
H
O H
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Reactions of metals carbonates with acid
A metal carbonate is an alkaline compound containing a metal,
carbon and oxygen.
METAL CARBONATE + ACID
Mg
O
O
H
C
O
H
SALT + CARBON DIOXIDE + WATER
Cl
O
Cl
Cl
Mg
Cl
C
O
Copy and complete the following reactions:
1) Magnesium carbonate + hydrochloric acid
2) Calcium carbonate + hydrochloric acid
3) Sodium carbonate + sulphuric acid
H
O
H
Making alkalis
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Large-scale industrialisation caused a shortage of alkalis in the
19th century, so a new method had to be found:
I’m an old scientist. I used to make alkalis
from limestone and salt using coal as a fuel.
The only problem was that it made a lot of
pollution – hydrogen chloride (an acidic gas)
and large piles of toxic hydrogen sulfide.
What’s the solution? One solution could be to turn the waste
products into something useful – for example, oxidation can
convert hydrogen chloride into chlorine, which can be used to
kill germs and as an ingredient in bleach.
Chlorine in Drinking Water
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Since chlorine was introduced in drinking water in the early
1900s the incidences of water-borne diseases has decreased
dramatically:
However, there other problems caused when chlorine reacts
with organic materials in the water.
Electrolysis of Salt Water
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Salt water (e.g. seawater or brine) can be
electrolysed using an electric current to produce
chlorine and other useful products:
Chlorine gas (Cl2) – useful
for making bleach and
plastics
Hydrogen gas (H2) –
useful as a potential fuel
source or manufacture
of HCl
Sodium
chloride
solution (salt
water)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq)) – useful
for making soaps and
manufacture of paper
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C3.4 What can we do to make our use
of chemicals safe and sustainable?
Harmful Chemicals
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There are a large number of industrial chemicals with many
widespread uses. The problem is, there can be a lack of
evidence that these chemicals might be harmful. Consider the
example of asbestos:
Asbestos was widely used in
buildings but banned in 1986 due to
its effects on the respiratory
system.
There are other
chemicals in the
environment that can
persist for many years
and be carried over
large distances. Eek!
Uses of PVC
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PVC stands for polyvinylchloride and has many uses:
Poly(chloroethene), PVC
PVC contains carbon,
hydrogen and chlorine. The
problem with PVC is that it
has “plasticizers” in it that
modify its properties and
make it stronger – these
plasticizers can leak out of
the PVC into the environment.
Life Cycle Assessments (LCAs)
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Step 1: Manufacture
What resources are needed? What effect
will this have on the environment?
Step 2: Use
How much energy will be needed? What is
the effect on the environment?
Step 3: Disposal
How is the product disposed of? What is the
effect on the environment?