Transcript C1 Unit 5 - Queen Elizabeth High School, Hexham

C1
Earth Chemistry
Limestone
Limestone
• Limestone is a rock made mainly of calcium carbonate
(CaCO3)
• It was formed from the remains of animals millions of
years ago and can be quarried
• Limestone can be heated with clay to make cement
• Cement is mixed with sand to make mortar
• Cement is mixed with water, sand and crushed rock to
produce concrete
• Heating limestone breaks it down – this is thermal
decomposition
Calcium carbonate  calcium oxide + carbon dioxide
CaCO3  CaO + CO2
Past paper questions
• Do question 2
• Foundation tier – do q.3
• Higher tier – do q.4
you have 3 minutes
Carbonates
• Buildings made of limestone are damaged by acid
rain
• When this happens, carbon dioxide is given off
• Carbon dioxide turns limewater cloudy
• The carbonates of magnesium, copper, zinc, calcium
and sodium can be thermally decomposed too
• They always form a metal oxide and carbon dioxide
e.g.
Magnesium carbonate  magnesium oxide + carbon dioxide
MgCO3  MgO + CO2
Uses of calcium oxide
• When limestone is thermally decomposed it
produces calcium oxide
• When calcium oxide is added to water it produces
calcium hydroxide
• Calcium hydroxide can be filtered to produce
limewater
• Calcium hydroxide is an alkali. It can be used to
neutralise acids. It is used by farmers to neutralise
acidic soil, and to neutralise acidic industrial gases.
Past paper questions
• Do questions 7 & 8
You have 8 minutes
Changes in the Earth and its atmosphere
Structure of the Earth
Crust: thin and
rocky
Mantle: flowing
rock
Core: mixture
of nickel and
iron
(inner core =
solid
outer core =
liquid)
• The Earth is made up of many layers
• The Earth is surrounded by the atmosphere
Tectonic plates
• The crust and mantle are broken up into large pieces
(tectonic plates)
• They move a few centimetres per year due to
convection currents in the mantle
• Earthquakes are caused when plate boundaries meet
and push together
Past paper questions
A newspaper reported that an earthquake off the coast of Kent
had caused plaster to come down from ceilings, house tiles to
loosen and church bells to ring.
(a) Suggest why the earthquake in Kent was reported and why
most earthquakes in the UK are not reported. (2)
(b) Explain how earthquakes are caused.
(3)
(c) People living in Kent were not warned about this earthquake.
In terms of what is happening within the Earth, explain the
problems of trying to predict earthquakes.
(2)
(Total 7 marks)
Answer
(a) (Kent reported because) damage was caused or it was
above 3 (on the Richter scale)
accept description of damage (1)
(others not reported because) no vibrations / not felt / not
noticed (allow below 3 (on Richter scale)) ignore no
damage (1)
(b) movement of (tectonic) plates (allow collision of plates
or plates rubbing together or plates pushing against each
other) (1)
any two from:
• vibration / (shock)waves (in the earth) or p and s waves
(accept sudden jolts / slips)
• caused by convection currents (in the mantle)
• heat / energy released from radioactive processes
Answer (continued)
(c) any two from:
scientists do not know:
• what happens under the crust / mantle / under the
surface (accept anything under the crust)
• where forces / pressures are building up
• how to measure these forces / pressures
• when these forces / pressures reach their limit
(accept there is no pattern; ignore random / speed of
movement) (2)
The modern atmosphere
• The Earth’s atmosphere
has been the same for
about 200 million years
The early atmosphere
• There are lots of theories
• One suggests that there was intense volcanic
activity about 4.5 billion years ago when the Earth
formed
• This released carbon dioxide, water vapour and
nitrogen gas – this formed the first atmosphere
• The water vapour condensed and fell as rain, this
formed the first oceans
• When life evolved plants released oxygen
• The amount of oxygen in the atmosphere increased
and animals could evolve
Carbon
• Most of the carbon dioxide from the Earth’s early
atmosphere has been taken up by plants, which were
eaten by animals, which were turned to sedimentary
rocks
• This means that most of the carbon is ‘locked’ in rocks
and in fossil fuels
• Carbon dioxide also dissolved in oceans
• Over the past 200 million years the amount of carbon
dioxide in the atmosphere has not changed much
The carbon cycle
• Using fossil fuels is increasing the amount of carbon
in the atmosphere again
Past paper question
Billions of years ago, the Earth’s early atmosphere was probably like the atmosphere of
Venus today.
The table shows a comparison of the atmospheres of the Earth and Venus today.
Percentage composition of atmosphere
Name of gas
Earth today
Venus today
Nitrogen
78
3.5
Oxygen
21
a trace
Argon
0.97
a trace
Carbon dioxide
0.03
96.5
Average surface temperature 20 ºC
460 ºC
(a) Use the names of gases from the table to complete the sentences.
(i) In the Earth’s atmosphere today, the main gas is .................................................. .(1)
(ii) In the Earth’s atmosphere billions of years ago, the main gas was
............................................................(1)
(b) (i) Scientists do not know the accurate composition of the Earth’s early atmosphere.
Suggest why. (1)
(ii) Use information from the table to answer this question.
Water vapour is present in the atmospheres of the Earth and Venus today.
The Earth’s surface is mainly covered by water.
Suggest why there is no water on the surface of Venus. (1)
Answer
(a) (i) nitrogen / N2
1
(ii) carbon dioxide / CO2
1
(b) (i) humans / scientists had not evolved
accept it was billions / millions of years ago
allow too long ago
1
(ii) temperature is above 100°C or any water
would evaporate / boil
accept Venus is too hot
1