Transcript Biology revision

C1- Chemistry in our world
17 July 2015
A Massawe
How science works
• Independent variable – this is the quantity that you
change
• Dependent variable - this is what you measure
• Control variable – this is what must be kept the
same to ensure a fair test
• Hypothesis – an idea based on observations without
experimental evidence
• Secondary evidence - data collected by someone
else, you may find it in a book or on the internet
17 July 2015
A Massawe
2
How do scientist validate results?
1. they repeat experiment results
2. they publish their findings in scientific journals
3. conference presentation
4. peer review/other scientists investigate the
same findings.
17 July 2015
A Massawe
3
The early atmosphere
• The early atmosphere was mostly carbon
dioxide, little oxygen, water vapour, ammonia.
• As the Earth cooled down, most of the water
vapour condensed and formed the oceans.
17 July 2015
A Massawe
Changes in the atmosphere
• The proportion of oxygen went up because of
photosynthesis by plants.
• The proportion of carbon dioxide went down
because:
1. it was locked up in sedimentary
rocks such as limestone
2. it was absorbed by plants for
photosynthesis
3. it dissolved in the oceans.
17 July 2015
A Massawe
Types of rock
1. Igneous rocks are formed by magma from the
molten interior of the Earth When it cools slowly inside the
earth it forms intrusive rock e.g.
granite.
When it cools on the surface is
known as extrusive rock e.g. basalt.
17 July 2015
A Massawe
Types of rock
2. Sedimentary rocks – As a river enters the sea it
slows down and deposits the sediment it was
carrying
Over millions of years the sediment is buried by
more and more sediment.
Eventually, as the water is squeezed out, it is
cemented together to form sedimentary rock.
sandstone
17 July 2015
A Massawe
limestone
Types of rock
3. Metamorphic rocks – is formed when existing
rock is changed by high temperatures and
pressures, e.g.
marble - which originates from
chalk or limestone
slate - which originates from clay
17 July 2015
A Massawe
Reactions of calcium compounds
17 July 2015
A Massawe
What are acids?
• Acids have a low pH (1-6) – the lower the
number the stronger the acid
• Acids react with bases to form salts and water
• are corrosive when they are strong
• are an irritant when they are weak.
17 July 2015
A Massawe
Indigestion remedies
• Hydrochloric acid (HCl)is used in the body to
help digestion and kill bacteria
• Too much acid can cause indigestion and we use
gaviscon to neutralise excess acids.
17 July 2015
A Massawe
Neutralisation
• is the reaction between an acid and a base to
form a salt and water.
1. Reaction of acids with metal hydroxides
hydrochloric + sodium → sodium +
chloride
acid
hydroxide
HCl
17 July 2015
+
NaOH
→
A Massawe
NaCl
+
water
H2O
Neutralisation
2. Reaction of acids with metal oxides
hydrochloric + copper → copper + water
chloride
acid
oxide
2HCl
+
CuO
→
CuCl2 + H2O
3. Reaction of acids with metal carbonates
hydrochloric + calcium → calcium + water + carbon
acid
carbonate chloride
dioxide
CaCO3
17 July 2015
+ 2HCl
→
CaCl2 + H2O + CO2
A Massawe
Electrolysis of copper chloride
• Electrolysis is the process by which ionic
substances are broken down into simpler
substances using electricity.
positive electrode
negative electrode
chlorine gas
given off
copper chloride
17solution
July 2015
copper metal
deposited
A Massawe
Electrolysis of water
water  oxygen + hydrogen
2H2O →
O2
2H2
oxygen
collected here
hydrogen
collected here
negative
electrode
17 July 2015
+
positive
electrode
A Massawe
Electrolysis
Electrolysis of:
dilute hydrochloric
acid
water
Produces:
oxygen
chlorine hydrogen
√
√
sea water
17 July 2015
√
√
A Massawe
√
√
Uses of products in the chemical
industry
Product
Test
Uses
damp blue litmus make bleach
paper turns red make plastics
e.g. PVC
Chlorine (as chlorine is
acidic) then
treat our water
white (chlorine is suppy
a bleach)
lighted splint gives fuel
Hydrogen a squeaky pop
Sodium turns red litmus cleaning products
hydroxide blue
17 July 2015
A Massawe
Problems
toxic gas
flammable
corrosive
Metal ores
• Ores are naturally occurring rocks that contain
metal or metal compounds, e.g.
bauxite, Al2O3
17 July 2015
haematite, Fe2O3
A Massawe
Reactivity and extraction method
most
reactive(hard
to extract)
Metal
Reactivity
potassium
sodium
calcium
magnesium
Aluminium
Electrolysis of a molten compound
Carbon
zinc
iron
tin
lead
Copper
least
reactive(easy
to extract)
17 July 2015
Heat an ore with carbon
Hydrogen
silver
gold
platinum
Found as the uncombined element
A Massawe
Oxidation and reduction
• Oxidation is the gain of oxygen by a substance
e.g.
magnesium + oxygen → magnesium oxide
2Mg + O2 
2MgO
• Reduction is the loss of oxygen from a
substance e.g.
copper oxide + hydrogen → copper + water
CuO +
H2
 Cu + H2O
17 July 2015
A Massawe
Rusting
• Iron and steel rust when they come into contact
with water and oxygen : this is a form of corrosion
• iron + oxygen → iron oxide (rust)
• Rusting is an oxidation reaction
17 July 2015
A Massawe
Uses of metals
Metal
Properties
Uses
low density, does
not corrode
suitable for the
bodies of planes
good conductor of
electricity, does not
react with water
electrical wires &
water pipes
aluminium
copper
gold
very good conductor electrical connections
on circuit boards &
of electricity,
jewellery
unreactive
cheap and strong
17 July 2015
steel
A Massawe
suitable for building
material
Alloys
• Alloys are made by mixing a metal with another
material e.g. steel (iron and carbon),
brass (copper and zinc) and bronze (copper and tin)
atoms from different
material are smaller
hence change
arrangement, this
makes alloy harder
and stronger
17 July 2015
A Massawe
Shape memory alloys
• Nitinol is a shape memory
alloy, its made from nickel
and titanium
• It returns to its original
shape when heated
• Used for spectacle frames
and hold the artery open
17 July 2015
A Massawe
Combustion of fuels
1. Complete combustion
methane + oxygen → water + carbon dioxide
2. Incomplete combustion
methane + oxygen → water + soot + carbon
monoxide
17 July 2015
A Massawe
Combustion of fuels
• The combustion of a fuel may release several
gases into the atmosphere, including:
1. water vapour
2. carbon dioxide
3. carbon monoxide
4. particles
5. sulfur dioxide
17 July 2015
A Massawe
Problems with fuels: sulfur dioxide
• Sulfur dioxide
is produced when fuels that contain
sulfur compounds burn.
acid rain is formed when sulfur
dioxide dissolves in water droplets
in clouds.
• Effects of acid rain
acid rain reacts with metals and
rocks such as limestone.
buildings and statues are damaged
as a result.
17 July 2015
A Massawe
Reducing the amount of carbon
dioxide
• Adding iron compounds to the sea
• Capturing carbon dioxide from the fossil-fuelled
power stations and reacting it to make
hydrocarbon compounds, e.g. propane and
butane which can be used as a fuel
17 July 2015
A Massawe
Iron seeding flow chart
Adding iron compounds encourages small plants
to grow
Small plants use carbon dioxide for
photosynthesis and then eaten by sea animals
When these animals die and sink to the ocean
floor, the carbonate in their shells is buried
This removes the carbon from the atmosphere for
along time
17 July 2015
A Massawe
Biofuels
• Methane biogas comes from
decaying manure and sewage.
• Some biodiesel is made from
waste cooking oil and rapeseed
oil.
17 July 2015
A Massawe
Advantages and Disadvantages of
Biofuels
Advantages
Disadvantages
It is a renewable resources
It more expensive than normal
diesel fuel
It less suitable for use in low
temperatures
It gives out more nitrogen oxide
emissions
It can only be used in dieselpowered engines.
It causes less pollution
It produces 78% less carbon
dioxide
It contains no sulfur, the
element responsible for acid
rain.
It is relatively less inflammable
compared to the normal diesel
17 July 2015
It is made from food crops
A Massawe
Factors influencing the choice of a fuel
•
•
•
•
•
•
the energy value of the fuel in J/g of fuel
the availability of the fuel
how the fuel can be stored
the cost of the fuel
the toxicity of the fuel - whether it is poisonous
any pollution caused when the fuel is used, such
as acid rain
• how easy it is to use the fuel
17 July 2015
A Massawe
Hydrocarbons and alkanes
• Hydrocarbon – contain hydrogen and carbon
atoms only, joined together by chemical bonds
• The general formula for alkanes is – CnH2n+2
• Alkanes are saturated hydrocarbons
alkane
formula
methane
CH4
ethane
C2H6
propane
17 July 2015
C3H8
chemical
structure
A Massawe
ball-and-stick
model
Distillation
• Distillation is a process that can be used to
separate a pure liquid from a mixture of liquids
• This is the sequence of events in distillation:
heating → evaporating → cooling → condensing
17 July 2015
A Massawe
Cracking
• Cracking is the process in which heavy oils are
broken down into hydrocarbons of lower
molecular weight by heat or catalysis
• Cracking allows large hydrocarbon molecules to
be broken down into smaller, more useful
hydrocarbon molecules.
butane
17 July 2015
ethane +
A Massawe
ethene
Alkenes
• Alkenes are product of cracking, they all have
general formula of CnH2n
• Alkenes are unsaturated hydrocarbons
alkene
formula
ethene
C2H4
propene
C3H6
17 July 2015
chemical
structure
A Massawe
ball-and-stick
model
Testing for alkenes
• An alkene will turn brown bromine water
colourless as it reacts with the double bond.
17 July 2015
A Massawe
Polymers
• Alkenes can be used to make polymers
• Polymers are very large molecules made when
monomers join together, end-to-end.
• Alkenes are monomers because they have a
double bond
ethene
17 July 2015
poly(ethene) or polythene
A Massawe
Uses of polymers
Monomer
ethene
Polymer
Properties
Uses
poly(ethene)
flexible,
cheap,
electrical
insulator
plastic bags and
bottles, coating
on electrical
wires
flexible and
poly(propene)
strong
buckets and
crates
propene
chloroethene
tetrafluoroethene
17 July 2015
tough, cheap
poly(chloroethe
and long
window frames
ne) or PVC
lasting
tough and
poly(tetrafluoro
non-stick coating
non-stick
ethene) or PTFE
on pans
A Massawe
Polymer problems
• Polymers are suitable for storing food and
chemicals safely
• Most polymers are not biodegradable.
• This means that microorganisms cannot break
them down, so they may last for many years in
rubbish dumps.
17 July 2015
A Massawe