Transcript carbon dioxide - Life Learning Cloud

C1 Revision
Topic 1
The fundamental ideas in chemistry
The periodic table of elements
• Everything is made from elements
• The periodic table of elements shows us metals (left)
and non-metals (right)
• Each element has a symbol… Sodium is ‘Na’ and Carbon
is ‘C’
• Each group has similar chemical properties
Atoms
• A particle of an element is
called an atom e.g. a carbon
atom, a sodium atom
• Atoms have the same
amount of positive and
negative charges so they are
neutral
Type of sub-atomic particle Relative charge
Proton
Neutron
Electron
+1 (positive)
0 (neutral)
-1 (negative)
Mass number
Atomic number
• Elements in the periodic table are arranged in order
of their atomic number
• atomic number = number of protons
• No. of protons = no. of electrons (protons and
electrons cancel each other’s charges out)
• The mass number = no. of protons + neutrons
• No. of neutrons = mass no. – atomic no.
Arrangement of electrons
• Electrons are arranged around the nucleus of
atoms in shells
• The first shell can hold up to 2 atoms
• The second shell can hold up to 8 atoms
• The third shell can hold up to 8 atoms
• Then the fourth shell fills up
Lithium
2,1
Arrangement of electrons
Fluorine
2,7
Chlorine
2,8,7
Calcium
2,8,8,2
Electrons and the periodic table
• Elements in the same group all have the same
number of electrons in their outer shell
• This means that they share similar properties
• Group 1 elements all have 1 electron in the outer
shell – they are all very reactive
• Group 0 elements (noble gases) have full outer
shells – they are unreactive
Group 1 – alkali metals
• Lithium, sodium and potassium all react violently
with water
• They form salts which are alkaline in pH
Lithium + water  lithium hydroxide + hydrogen
Sodium + water  sodium hydroxide + hydrogen
potassium + water  potassium hydroxide + hydrogen
Forming compounds
• When atoms of different types of elements join
together they form ‘compounds’
• Sometimes atoms react by transferring electrons – this
happens when metals react with non-metals and forms
ions
• Metals lose electrons and become positive ions (+)
• Non-metals gain electrons – negative ions (-)
• These ions are attracted to each other and form an
ionic bond
Ionic bonds
Forming molecules
• Sometimes atoms react by sharing electrons – this
happens when non-metals react with non-metals
• This is called covalent bonding
Chemical formulae
• This tells us the number of atoms in a compound
or molecule
•
•
•
•
•
•
CH4
H2O
MgCl2
CaCO3
Fe2O3
2C2H5OH
- 1 x Carbon, 4 x Hydrogen
- 2 x Hydrogen, 1 x Oxygen
- 1 x Magnesium, 2 x Chlorine
- 1 x Calcium, 1 x Carbon, 3 x Oxygen
- 2 x Iron, 3 x Oxygen
- 4 x Carbon, 11 x Hydrogen, 1 x Oxygen
Chemical equations
• These show us the reactants (the substances we start
with) and the products (the substances made)
calcium carbonate  calcium oxide + carbon dioxide
CaCO3  CaO + CO2
• The equation is balanced – the same number of atoms
are going in and are coming out of the reaction
• The total mass of the products formed in a reaction is
equal to the total mass of the reactants
Topic 2
Limestone and building materials
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
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.
Topic 3
Metals and their uses
Extracting metals
• Metals are found in the Earth’s crust
• They are often chemically combined with
other elements – this is called the ore
• Whether it is worth extracting a metal
depends on:
1. How easy it is to extract it from its ore
2. How much metal the ore contains
Transition metals
Extracting metals
• The way we extract a metal depends on its place in
the reactivity series
Most reactive
Least reactive
Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Platinum
electrolysis
carbon
reduction
Other
methods
Carbon reduction
• A more reactive metal will displace a less reactive
metal from its compounds
• Many metals combine with oxygen – carbon will
also displace less reactive metals from their oxides
when heated with them
Metal oxide + carbon  metal + carbon dioxide
Lead oxide + carbon  lead + carbon dioxide
2PbO + C  2Pb + CO2
Iron
• Iron ore contains iron combined with oxygen
• Iron is extracted using carbon reduction
• It is heated in a blast furnace
Iron (III) oxide + carbon  iron + carbon dioxide
• Iron straight from the blast furnace still contains some
impurities (it is about 96% iron) – it is very brittle and is
called cast iron. It can be used to mould different
shapes
• Removing the impurities gives us pure iron – this is too
soft for most uses
Iron
• To make iron useful we can add small amounts of
other elements
• A metal that is mixed with other elements is called
an alloy
• Steel is an alloy of iron
• Carbon steel contains between 0.03% and 1.5%
carbon
Low carbon steels are easily shaped
High carbon steels are very strong
• Iron with chromium and nickel makes stainless steel
Aluminium
• Aluminium is a very low density metal
• It can be alloyed with other elements to make it
very strong
• It cannot be extracted from its ore by carbon
reduction because it is more reactive than carbon
• It is extracted using electrolysis instead – an electric
current is passed through molten aluminium oxide
at high temperatures to break it down
• Electrolysis is very expensive because lots of energy
is needed – this is why we recycle aluminium
Titanium
• Titanium is very strong and has a very high melting
point
• It is used for jet engine parts, replacement hip
joints and as nuclear reactor parts
• It cannot be reduced using carbon because it is
more reactive
• It is reduced using sodium or magnesium, but this
process is very complicated and has lots of steps,
which means the titanium is very expensive
Copper
• Pure copper is a good conductor of electricity, does
not react with water and can be shaped easily
• Copper can be removed from its ore by smelting
• This involved heating it in a furnace:
Copper (I) sulfide + oxygen  copper + sulphur dioxide
Copper
• The copper produced is purified using electrolysis
• This involves passing an electrical current through a
copper solution
Copper
• Copper-rich ores are running out
• New methods are used to extract copper from low
grade ores
• Phytomining – using plants to extract copper
• Bioleaching – using bacteria to extract copper
• 20% of our copper comes from bioleaching
More alloys
• Bronze = copper + tin
this is tough with resistant to corrosion (used to make
statues)
• Brass = copper + zinc
this increases the strength of copper but is still
malleable (used to make musical instruments)
• Gold can be alloyed to increase its strength
• There are over 300 aluminium alloys with different
properties
Topic 4
Crude oil and fuels
Crude oil
• Crude oil is a fossil fuel that was formed millions of
years ago from the remains of sea creatures
• It is a dark, thick liquid containing a mixture of lots
of different chemical compounds
• We separate the different compounds by fractional
distillation
• This involves separating the different fractions
depending on their boiling points
Crude oil
• Crude oil contains compounds made of only
hydrogen and carbon – hydrocarbons
• Most of the hydrocarbons are alkanes
• The general formula for alkanes is CnH(2n+2)
• Alkanes are saturated hydrocarbons because they
are full – no more bonds can be made
Alkanes
Methane Ethane
C2H6
CH4
Propane
C3H8
Butane
C4H10
Properties of hydrocarbons
Chain length:
Boiling point:
Low
High
Volatility
High
Low
(how easily it flows):
Low
(very runny)
High
(very thick)
Flammability
High
Low
(tendency to turn into gas):
Viscosity
(how easily it burns):
Fractional distillation of crude oil
Combustion
• When hydrocarbons are burned in air they release
energy – this ‘oxidises’ the hydrogen and the carbon in
the fuel (oxygen from the air is added)
• This is called complete combustion
Propane + oxygen  carbon dioxide + water
C3H8 + 5O2  3CO2 + 4H2O
• The carbon dioxide released can cause global warming
• Incomplete combustion happens when there is not
enough oxygen – carbon monoxide (CO) is produced
instead of carbon dioxide (CO2) – this is a poisonous gas
Pollution from hydrocarbons
• Fossil fuels contain sulfur
• When they are burned it releases sulfur dioxide
• This is a poisonous gas that causes acid rain
• High temperatures inside car engines can cause
nitrogen and oxygen to react forming nitrogen oxides
• These are poisonous and can trigger asthma and cause
acid rain
• Diesel engines can release particulates – these are tiny
particles of carbon released into the air – these can
cause global dimming
Cleaner fuels
• A catalytic converter can be fitted to a cars exhaust
to reduce the amount of carbon monoxide and
oxides of nitrogen released
carbon monoxide + nitrogen oxides  carbon dioxide + nitrogen
• In power stations, sulfur dioxide can be removed
from waste so it isn’t released into the atmosphere
• Sulfur impurities can also be removed from fuels
before combustion
Biofuels
• Fossil fuels are running out – an alternative is biofuels
made from plant or animal products
• Biodiesel is made from oils from plants
• It produces less pollution than diesel
• Using land for biodiesel plants instead of food crops
could cause problems
• Ethanol is made from fermented sugar cane
• Ethanol can be mixed with petrol to save money
• Ethanol still gives off carbon dioxide when burned, but
the sugar cane plant absorbs CO2 for photosynthesis
Topic 5
Other useful substances from crude oil
Cracking
• After fractional distillation of crude oil, we are left
with lots of less useful long-chain hydrocarbons
• Long-chain hydrocarbons can be broken down in a
process called cracking
• This involves heating the fraction until it vapourises
then passing it over steam or a hot catalyst
Cracking hexane
(800°C + hot catalyst)
Hexane  butane + ethene
C6H14  C4H10 + C2H4
Testing alkanes and alkenes
• Bromine water reacts with alkenes and
forms a colourless solution
Unsaturated hydrocarbon + bromine water 
colourless solution
• The double bond opens up and reacts
• Bromine water remains orange in
alkanes
Saturated hydrocarbon + bromine water 
orange solution
• The hydrocarbon cannot make any more
bonds and doesn’t react
Polymers
• Hydrocarbon molecules can be used to make
plastics
• Small molecules are called monomers
• Lots of monomers joined together make polymers
Polymerisation
Chloroethene monomers
A section of poly chloroethene (PVC)
Polymers
A repeating unit of poly chloroethene (PVC)
New polymers
• New plastics with special properties are being
developed
• Dental fillings, waterproof fabrics and light sensitive
plasters are made with special polymers
• Smart polymers such as shape memory polymers
‘remember’ their original shape and will return to it
when heated e.g. stitches closing a wound using
body heat
Plastic waste
• Many polymers are not biodegradable – this means
microorganisms cannot break them down
• New biodegradable polymers have been developed
using starch and plant products that
microorganisms can break down
• This reduces the amount of plastics in landfills
Ethanol
• This is the type of alcohol found in
alcoholic drinks
• Its formula is C2H5OH
• Ethanol can be made by fermentation of sugar from
plants with yeast
Glucose (sugar)  ethanol + carbon dioxide
C6H12O6  2C2H5OH + 2CO2
• Ethanol can also be produced by reacting ethene (from
cracking crude oil) with steam
• A catalyst is used to speed up the reaction
Ethene + steam  ethanol
C2H4 + H2O  C2H5OH
Topic 6
Plant oils and their uses
Vegetable oil
• Some fruits, seeds and nuts are rich in oils that can
be extracted
• The plant material is crushed and the oil is removed
by pressing or distillation
• Water and other impurities are removed
• Vegetable oils provide nutrients and have a high
energy content
• They are important foods and can be used to make
biofuels
Vegetable oil
• Vegetable oils contain hydrocarbons
• Unsaturated oils with C=C bonds can be detected
using bromine water – they decolourise it
Unsaturated oil + bromine water  colourless solution
• Vegetable oils have higher boiling points than water
• Foods can be cooked at higher temperatures than
by boiling
• Food cooks faster and has different flavours
• Food cooked in vegetable oil releases more energy
when it is eaten (increased calorie content)
Emulsions
• Oil does not mix with water
• An emulsifier is a special molecule that can be used
to mix them and create an emulsion
• Emulsions include ice cream and mayonnaise
• Without an emulsifier, the oil and water would
separate out into layers
Topic 7
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
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