Transcript C2 Revision - Purbrook Park School

C2 Revision
Contents
•
•
•
•
•
•
•
•
•
•
•
•
•
The Structure of the Earth
Volcanoes and Igneous Rocks
Construction Materials
Limestone, Marble and Granite
Copper
Alloys
Iron and Aluminium
Cars
Haber Process
Acids and Alkalis
Fertilisers and Crop Yield
Making Fertilisers
The Chemistry of Salt
The Structure of the Earth
• The Earth has 4 main
Layers.
• The lithosphere describes
the crust and the outer
part of the mantle
• The Mantle is the thickest
layer
• The Crust is not of a
uniform thickness.
Plate Tectonics
• The crust is made up of a number of different plates called tectonic
plates. These float on top of the mantle as they are less dense. They
move, very slowly.
• As a result of this movement, the surface of the planet has changed
greatly over millions of years. It is thought that once, all of the
landmass was close together, in a supercontinent called Pangea.
• The movement of plates also causes volcanoes, earthquakes and
mountains.
Plate Tectonics
• The core of the earth is much hotter than the surface. As a result,
convection currents occur in the mantle, where the bottom of the
mantle is heated, becomes less dense, rises, cools and sinks again.
This causes the plates of the crust to move.
Volcanoes
• When the magma of the mantle escapes through the crust, volcanoes
occur. These, along with earthquakes, occur along the lines where
different plates meet. These are called fault lines. The map that we
saw in class demonstrated that these things occur along known fault
lines.
When happens when the plates move?
lithosphere of
oceanic plate
friction between the
plates causes
earthquakes
some molten rock
rises to the surface
to form volcanoes
lithosphere of
continental
plate
oceanic floor is
more dense
than a
continent so
it sinks when
plates collide
the sinking rock pulls more of
the plate down – this is
subduction
the subducted rocks partially remelt and become part of the
mantle
What makes some eruptions more
dangerous?
• Some eruptions produce runny lava. These eruptions are safer. Other
eruptions produce thick lava that that escapes violently. Geologists
study volcanoes to try to predict future eruptions, and to gather
information about the Earth’s structure. Volcanoes can be very
destructive, but some people choose to live near them because
volcanic soil is very fertile. It contains minerals needed by plants for
healthy growth
• Basalt is rich in iron - it formed from runny lava produced in a fairly
safe volcanic eruption
• Rhyolite is rich in silica - it formed from thick lava produced in an
explosive eruption.
Alfred Wegener
• The theory of plate tectonics and continental drift was proposed at
the beginning of the last century by German scientist, Alfred
Wegener.
• Wegener suggested that mountains were formed when the edge of a
drifting continent collided with another, causing it to crumple and
fold. For example, the Himalayas were formed when India came into
contact with Asia. It took more than 50 years for Wegener’s theory to
be accepted, beacuse:
• it was difficult to work out how whole continents could move
• it was not until the 1960s that enough evidence was discovered to
support the theory fully.
Evidence to Support Wegener
• the same types of fossilised animals and plants are found in South
America and Africa
• the shape of the east coast of South America fits the west coast of
Africa, like pieces in a jigsaw puzzle
• matching rock formations and mountain chains are found in South
America and Africa
• In the 1950s, evidence from magnetism in the ocean floor showed
that the seafloors were spreading by a few centimetres each year.
This showed movement of large parts of the Earth’s crust, now called
tectonic plates
Igneous rocks are formed when magma cools above or below ground. If
the lava cools above ground, the rocks are called extrusive igneous rocks.
These cool quickly and form small crystals. If the magma cools below
ground, the rocks are called intrusive igneous rocks. The cool more slowly
and form larger crystals.
It tends to be that the larger the crystal, the stronger the rocks that are
formed.
Different Types of Rock
Type of rock
Sedimentary
Metamorphic
Igneous
Example
Limestone
Marble
Granite
Hardness
Soft. Made from
layers of different
materials stuck
together over
time. Therefore
not held together
very strongly.
Quite hard. To form
the marble limestone
is subjected to heat
and pressure, this
pushes the particles
together and makes it
stronger.
Very hard. Formed when
liquid rock cools.
Interlocking crystals are
formed which are held
together very strongly
making it hard.
Construction Materials
• Construction materials are a huge, diverse range of materials that we
use to build things. We pick these materials based on the following
factors:
• Cost
• Strength
• Availability
• Durability
Expensive
metamorphic
stone, popular in
bathrooms and
kitchens. Cut out
of the ground in
quarries. This rock
can withstand
many years of
weathering.
A common white
rock, quarried from
the ground. A
sedimentary rock that
is formed under sea
beds and can
sometimes have
fossils contained
inside. Because it is
such a soft rock it
can weather easily.
Used for
centuries to
build houses in
Britain, made
up of clay and
sand giving it a
red colour.
Strong, but not
weather proof.
Used to provide
strength as an
internal frame,
this metal is an
alloy of iron and
carbon. It is
also used for
cutlery!
Used as a
feature on the
outside of
buildings, a very
strong metal.
This metal is an
alloy of iron and
carbon.
This material is
commonly used in
greenhouses but
has proven to be
more popular in
large modern
buildings. Made
from lime (obtained
from limestone)
and sand.
Made from a light
metal that is more
commonly used in
car and bicycle
structures, this
metal is made
from metal ores
extracted from the
ground.
Making Cement
• Cement is a mixture of limestone and clay.
• It is made by heating limestone (calcium carbonate) so that it
thermally decomposes to make calcium oxide. This is then mixed with
clay.
• Calcium carbonate  Calcium oxide +
carbon dioxide
• CaCO3  CaO + CO2
Making concrete
• Concrete is an artificial rock made from mixing cement, sand, gravel
and water.
• Reinforced concrete has steel rods or a steel mesh running through it.
This is to make it stronger. When we add the steel, it enables to
weight to be spread more evenly throughout the concrete, meaning
that it won’t bend and crack.
Why do we need to reinforce concrete?
• Concrete is very hard.
• Steel is flexible
• Concrete is strong under compression (squashing) but much
weaker under tension (pulling)
• When we put a heavy load on concrete it will bend slightly.
• This means that the underside is put under tension and it can
start to crack.
• To prevent this we reinforce it with steel rods or mesh.
• Reinforced concrete is better because it combines the
hardness of concrete with the flexibility of steel.
Quarries
• A quarry is a large hole in the ground that has been dug, by humans,
so that the rocks within can be extracted. These rocks are then used
for building materials. Quarries have a large impact on their
surrounding areas:
Pros of Quarries:
• Enables large amounts of construction materials to
be removed
• Provides jobs for the local economy, strengthening
the economy in the nearby towns.
• Provides cheap materials which strengthens the
construction industry
• Because of the jobs, more people move to the
areas near quarries so they may work there.
• May be used as a landfill site when it is no longer in
use.
Cons of Quarries:
• Large amounts of pollution may be produced from
the quarrying machinery and from the transport of
the materials away from the site.
• May cause a large amount of dust in the
surrounding area.
• Puts off tourists as it is considered an eyesore.
• May lower surrounding house prices due to noise
and mess.
Obtained from
copper ore (found
in rocks)
Copper ore =
copper oxide
(CuO)
Separated by
displacement
with carbon
Copper
Purified by
electrolysis
Uses; electrical
wires, making
brass and bronze
Recycling copper
is cheaper; saves
resources and
saves energy
Problems with
recycling; people
may not recycle,
copper has to be
sorted from other
metals
Extracting copper using carbon
Cu
C
The carbon DISPLACES the
copper from copper oxide
because it is more reactive
Cu
Cu
O
Copper is being reduced because it is losing oxygen.
Carbon is being oxidised because it is gaining oxygen
O
Cu
O
C
O
What is happening in copper electrolysis?
Anode
As the anode
dissolves copper
atoms lose
electrons to form
copper ions;
Cu  Cu2+ + 2e
Cathode
2+
2+
2+
2+
When the ions get
to the cathode
they gain
electrons to
become pure
copper
Cu2+ + 2e  Cu
The copper ions are attracted to the cathode because they are positive
and it is negative. Any impurities drop to the bottom of the beaker
What is happening in copper electrolysis?
• Pure copper is plated at the cathode.
• The impure copper anode dissolves.
Problems with Recycling Copper
• Generally, recycling is known to be cheaper and greener than
producing more of a product from scratch. The recycling of copper is
no exception:
• Copper must be sorted from the other undesirable metals
• It must be purified again if it is to be used for things that require pure
copper.
• These both incur costs and may cause pollution.
What is an alloy?
An alloy is a mixture of a metal element and another
element (metal or non-metal).
E.g. Bronze = copper with small amounts of tin.
Brass = copper with small amounts of zinc
Alloy
Elements it contains
Used for
Reason
Brass
Copper and zinc
Taps, door
handles in
hospitals, musical
instruments
Shiny
Kills bacteria
Bronze
Copper and tin
Coins
Hard wearing
Steel
Iron and carbon
Bridges, cars
Hard wearing
Amalgam
Mercury (& silver, tin & Filling teeth
copper)
Soft when made and
hardens quickly
Solder
Lead and tin
Very low melting point
Joining metals
together
Alloys – improving metals
An alloy is a mixture of two elements, one of which is a metal.
Alloys often have properties that are different to the metals they contain. This
makes them more useful than the pure metals alone. For example, alloys are often
harder than the metals they contain.
Alloys contain atoms of different sizes, which
distorts the regular arrangements of atoms.
This makes it more difficult for the layers to
slide over each other, so alloys are harder
than the pure metal.
The carbon atoms
added to steel distort
the regular structure.
Smart alloys
• Smart alloys are alloys which change shape at different
temperatures.
• This is called “shape memory.”
• Nitinol is a smart alloy made from nickel and titanium
• Reducing risk of heart attack – a small piece of metal is put into a
blocked artery. It is then warmed, when this happens it changes
shape and becomes a much larger tube and holds the artery open.
• Preventing scalding by hot water – used in shower heads. If the
water gets too hot the water supply is reduced.
• Glasses – Recently glasses have been made from smart alloys. These
glasses were flexible and would return to their original shape,
preventing them breaking when they were trodden on, or bent by a
child.
Steel
• Steel is an alloy that is made from iron and carbon. Although there is
normally only a small amount of carbon present, there is enough to
distort the regular arrangement of the atoms which makes steel
incredibly strong. While Steel is incredibly strong and relatively cheap,
it can be corroded.
What is corrosion?
Corrosion is the reaction between a metal and oxygen to form
crystals or a powder (metal oxide).
All metals corrode but only iron rusts. Rust is a trivial name for
hydrated iron (III) oxide, so rusting is a form of corrosion.
Iron and aluminium
• Steel rusts and aluminium corrodes.
• For iron this is a problem for aluminium it is not why?
From the diagrams above, we can see that Iron Oxide has got gaps between it, which allows the oxygen and water in to
continue to corrode.
Aluminium oxide is a dense layer, so no oxygen or water can get through. This means that once the top layer of aluminium
has corroded, the rest of the metal is protected and will not continue to corrode.
Factors that influence corrosion
• The things can cause or increase corrosion are:
• Water in the air
• Salt in the air
• Acid rain (caused by pollution)
• Some metals corrode more than others, so by choosing metals that
corrode less, we can prevent objects from breaking.
Choosing the correct material for the job
• Cars used to be always made from steel. Steel was chosen as it is
incredibly strong, fairly cheap, conducts electricity and can be made
into different shapes.
• In the last 25 years, cars made from Aluminium has been on the rise.
Aluminium is slightly more expensive than steel, but does not corrode
and is lighter.
Properties of aluminium and steel
Property
Steel (Iron)
Aluminium
Does it corrode
easily?
Is it magnetic?
Yes – easily rusted.
Yes
No – forms a
protective layer.
No
Is it a good conductor
of electricity?
Very good
Not good.
Is it malleable?
Not much.
Yes.
How high is its
density?
Very dense (heavy)
Not very dense (light)
Advantages of Aluminium in Cars
• Because it is lighter, the car will have a better fuel efficiency as it will require
less fuel to accelerate and run
• Aluminium does not corrode, so the car will last much longer than a steel
based car. From the POV of the customer, this is good as it means that the
car will be a better investment. For the manufacturer, it is a double edged
sword; while the cars will gain a reputation for lasting longer and being
more reliable, people will buy a new car less often as their cars are lasting
much longer.
• Because it is more pliable then steel, it is easier to mould into shape, though
it will mean that damage caused to cars in accidents might be much more
extensive than the steel cars.
The Haber Process
• Ammonia is produced from Hydrogen and Nitrogen gases under high
pressure, with high heat and an iron catalyst.
• It is a reversible reaction and as a result, reaches equilibrium – This
means that the forward reaction and the backwards reaction are
happening at the same time and at the same rate.
• Ammonia is important has it has a large variety of uses, the most
important of which is for fertilising crops.
⇌ Ammonia
3H2 ⇌ 2NH3
Nitrogen + Hydrogen
N2
+
What is an Equilibrium
• An equilibrium is reached when the forwards reaction and the
backwards reaction start to happen at the same time at the same
rate. There are different ways to change an equilibrium:
• An increase in equilibrium will push the reaction in the endothermic
direction (where the heat is taken in)
• An increase in pressure will push the equilibrium towards the side
with the fewest amount of molecules
• A change in concentration of any of the reactants and products will
cause the equilibrium to shift to balance out the change.
Compressor – puts
the gas under
pressure
Nitrogen
Hydrogen
and
Nitrogen
react
Iron catalyst
(temp 4500C)
Hydrogen
Nitrogen and
hydrogen added
Unused gases are
recycled and reused
so reduces waste
Ammonia
Kept at low temp so that
ammonia is turned into a
liquid
Rate Vs Yield
• The reaction conditions of the Haber Process are said to be a compromise.
• When you increase the temperature of the reaction, the rate of the reaction increases, and the Haber Process
will reach equilibrium quicker. The increase in temperature decreases the yield of the reaction, as the forward
reaction is exothermic. Because of this, a temperature of 450 degrees Celsius is used, as the yield is sufficiently
high enough and the rate sufficiently quick enough to make the process economically viable.
• When you increase the pressure of the reaction, the yield and rate will increase. Increases in pressure of the
reaction cost money, as the machinery required to compress the gases costs money.
• To make the process more economically viable, the ammonia is condensed and siphoned away, and the
unreacted gases are recycled, so that there is no waste.
Factor
How it affects Cost
Cost of reactants
Hydrogen and nitrogen are needed these both have to be
separated which costs money.
Recycling unused
materials
This Saves money because reactants are not Wasted.
High pressure
The higher the pressure the more Complicated the plant.
Energy costs
The higher the temperature the Higher the energy costs.
Reaction speed
The faster the reaction the more product produced in a
certain amount of time so the more effective the
process.
Pollution controls
Reducing pollution requires specialised equipment
which is Increases the Cost.
Acids and Alkalis
• Acids and Alkalis are compounds that change the pH of a solution.
• pH is a measure of the concentration of H+ ions within a solution.
• We calculate pH with pH = -log[H+]
• Acids, such as HCl give a H+ ion when in solution. This means that the
pH will be low.
• Alkalis, such as NaOH, give OH- when in a solution. This means that
the pH will be high.
pH and universal indicator
Weak alkalis have
higher pH no’s
Weak acids have
higher pH no’s
pH
1
2
3
4
5
6
7
8
9 10 11 12 13 14
Colour
Strong acids have
low pH no’s
Neutral substances
are pH 7
Strong alkalis have
high pH no’s
Acid or alkali? Strong or weak?
Solution
Formula
Colour in UI
pH
Acid or
alkali?
Strong or
weak?
Hydrochloric
acid
HCl
Red
1
Acid
Strong
Sulphuric acid
H2SO4
Red
2
Acid
Strong
Nitric acid
HNO3
Red
1
Acid
Strong
Ethanoic acid
HOOCCH3
Orange
2.4
Acid
Weak
Phosphoric
Acid
H3PO4
Red
1
Acid
Strong
Sodium
hydroxide
NaOH
Purple
14
Alkali
Strong
Ammonium
hydroxide
NH4OH
Blue
11
Alkali
Weak
What happens when an acid reacts with an
alkali?
H
O
+
H
H
H
O
Reacting Acids and Alkalis
• Word equations for reactions:
• Acid + Alkali  Salt + Water
• Acid + Metal Oxide  Salt + Water
• Acid + Metal Carbonate  Salt + Water + Carbon Dioxide
Figuring out how to write the word equation
• We know how acids react with different compounds.
• When we see which acid is reacting, we can name the salt that is
produced:
•
•
•
•
Hydrochloric Acid, HCl will react to produce a Metal Chloride, Cl
Sulfuric Acid, H2SO2 will react to product a Metal Sulfate, SO4
Nitric Acid, HNO3 will react to produce a Metal Nitrate, NO3
Phosphoric acid, H3PO4 will react to produce a Metal Phosphate, PO4
• So we can see that the acids lose their hydrogen.
• The other products formed depend on the compound that the acid is reacting
with, just like in the word equations from the slide before.
Writing the Symbol Equation
• Group 1 Metals form a +1 ion, so they will replace 1 Hydrogen in an
acid.
• HNO3 + NaOH  NaNO3 + H2O
• Group 2 Metals and Transition Metals (that block in the middle) will
form a +2 ion, so they will replace 2 hydrogens in an acid.
• H2SO4 + CuCO3  CuSO4 + H2O + CO2
• 2HCl + CuO  CuCl2 + H2O
Fertilisers
• Plants require specific minerals to maintain good health. The three
most important elements that these minerals must contain are:
• Nitrogen (N)
• Phosphorous (P)
• Potassium (K)
• We ensure that plants get these essential elements using fertilisers. Fertilisers
have to be water soluble, as the plants absorb the compounds needed
through their roots. Salts are water soluble, easy to make and can be
designed to contain any of the elements that the plant needs.
Fertilisers
• Salts are made when we react acids with alkalis. We can deduce the
reactants that make the salt by looking at the name of salt.
• Ammonium Phosphate is made by the reaction between Ammonia
and Phosphoric acid:
• Phosphoric Acid + Ammonia  Ammonium Phosphate + Water
Using Fertilisers
• Influencing anything can have consequences, good and bad.
Fertilisers are no exception.
• Using fertilisers means that land can be used specifically for farming
constantly and crop rotation is not always necessary. It also increases
crop yield by making sure that all of the plants that grow are as
healthy as possible, which increases the chance of a good crop.
• The bad side is that as fertilisers are water soluble, they can be
washed into local water sources. This causes a process called
Eutrophication which is a problem for still bodies of water.
Eutrophication
Plants
photosynthesise
and produce oxygen
which is used by fish
for respiration
Sunlight can not
reach the plants
due to algal bloom.
This means they
stop producing
oxygen
Fish die due to lack
of oxygen. Plants
die due to lack of
oxygen and sunlight
Salt – Sodium Chloride
• Common Salt is the chemical Sodium Chloride, NaCl. It can be made
in a laboratrory by reacting sodium with chlorine.
• It is found naturally in large amounts in sea water or in underground
deposits. We then either evaporate the water, or mine the deposits.
• Salt can be mined as rock salt which is used on roads. It lowers the
melting point of ice so that it melts.
• Salt can also be mined by solution mining. This happens in Cheshire.
Water is pumped underground into the salt deposit. The salt
dissolved in the water forming a concentrated salt solution. It is then
pumped back to the surface.
Uses of Sodium Chloride
• Salt is widely used in the food industry as a preservative and flavour
enhancer. Too much salt is bad for us but we do require a certain
amount in our diet to be healthy.
• It is the raw material for the manufacture of hydrogen, chlorine and
sodium hydroxide by electrolysis. It’s an important process because
the substances produced have many industrial uses.
Electrolysis of Sodium Chloride Solution
2H+ + 2e-
H2 (hydrogen gas at the (-)cathode).
2NaCl(aq) + 2H2O(l)
2Cl- - 2e-
Cl2 (chlorine gas at the (+)anode).
2Na+(aq) + 2OH-(aq) + Cl2(g) + H2(g)
Products of Electrolysis of Sodium Chloride
• The products of the electrolysis of sodium chloride solution have important uses
in the chemical industry:
• Hydrogen
• Hydrogen is used in the manufacture of ammonia and margarine (it is used to harden vegetable oils).
• Chlorine
•
•
•
•
kill bacteria in drinking water and swimming pool water
make solvents
make plastics such as polyvinyl chloride (PVC)
make household bleach.
• Sodium hydroxide
• Sodium hydroxide is used to make soap and household bleach.
• Bleach
•
•
•
•
Household bleach, sodium chlorate, is made when sodium hydroxide and chlorine react together:
sodium hydroxide + chlorine → sodium chloride + water + sodium chlorate
2NaOH + Cl2 → NaCl + H2O + NaClO
Household bleach is used to clean and disinfect toilets, drains and kitchen surfaces.