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COOKING
Why cook food?
• Improves texture of the food
• Improves the taste
• Improve flavour
• High temperatures kill microbes
• It is often easier to digest
The process of cooking food is an example of a
CHEMICAL CHANGE because a new substance is
formed and the process cannot be reversed.
The changes that occur when an egg or meat is cooked:
• Change in appearance
• Change in texture
The protein in a raw egg has a 3D shape.
When an egg is cooked the protein molecules change
shape.
This change is called denaturing
Baking powder is used for baking cakes
Baking powder gives of CARBON DIOXIDE when
heated
The carbon dioxide helps make cakes rise
Test for carbon dioxide – turns Limewater from clear to
CLOUDY
Baking powder contains SODIUM
HYDROGENCARBONATE
The SHC breaks down when heated to make sodium
carbonate, carbon dioxide and water.
sodium hydrogencarbonate → sodium carbonate
+ carbon dioxide + water
2NaHCO3 →
NaCO3 + H2O + CO2
CLEAN AIR
•
•
•
•
Air contains oxygen, nitrogen, water vapour and
carbon dioxide
Oxygen, nitrogen and carbon dioxide levels in
the air are quite constant
Photosynthesis decreases the level of carbon
dioxide and increases the level of oxygen
Respiration and combustion increase the level of
carbon dioxide and decreases the level of oxygen
Composition of air
21% oxygen
78% nitrogen
0.035% carbon dioxide
Deforestation


Increased energy consumption (burning
of fossil fuels)
Populations
How the present day atmosphere evolved
Original atmosphere came from gases escaping
from the interior of the earth
Photosynthesis by plants increases the
percentage of oxygen until it reached today’s level
Theory for how the atmosphere evolved
Degassing from the earth’s crust
Initial atmosphere of ammonia and carbon
dioxide
Formation of water
Development of photosynthetic organisms
FOOD ADDITIVES
Food additives are added to foods to:
Help make the production of food easier and quicker
Improve certain properties of foods e.g. its colour or
taste
The main types of food additives are:
• Antioxidants
• Food colours
• Emulsifiers
• Flavour enhancers
Antioxidants = food reacting with oxygen. Examples
of foods containing antioxidants:
 Oranges = Vitamin C
Emulsifiers - Oil and water do not mix but emulsifiers
help oil and water to mix and not separate
These are molecules that have a:
•
Water loving part – HYDROPHILIC
• Oil loving part – HYDROPHOBIC
Examples : Egg yolk (used to make the emulsion
mayonnaise)
Packaging = Improves the quality or safety of food
There are two types of packaging:
Active = Involves the material controlling or reacting to
things which are taking place inside the package to
improve the quality or safety of the product
• Example – cans which will heat or cool
contents
Intelligent = Involves the removal of water which will
make it more difficult for bacteria or mould to grow.
Common pollutants
 Carbon monoxide – a poisonous gas.
Formed by the incomplete combustion
of petrol or diesel in car engines
 Oxides of nitrogen – photochemical
smog and acid rain. Formed in the
internal combustion engine
 Sulphur dioxide – formed when sulphur
impurities in fossil fuels burn
 Acid rain will kill plants, aquatic life,
erode stonework and corrode metals
Catalytic converter
A catalytic converter removes carbon monoxide
from the exhausts gases of a motor car by
turning it into carbon dioxide
2CO + 2NO → N2 + 2CO2
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FUELS
A “fuel” is something that can be burned in
OXYGEN to release heat and light energy. The
main examples are: Coal, oil and gas
Factors that need to be considered when choosing
a fossil fuel
Energy value
Availability
Storage
Cost
Toxicity
Pollution e.g. acid rain, greenhouse effect
Ease of use
COMBUSTION means ‘Burning’
It needs OXYGEN.
Combustion of a fuel releases useful HEAT energy.
Complete Combustion - This needs a plentiful
supply of Oxygen
• It produces CARBON DIOXIDE and
WATER
Incomplete Combustion • This takes place when there is a
SHORTAGE of Oxygen.
• Incomplete combustion of a hydrocarbon
fuel produces CARBON MONOXIDE,
CARBON (SOOT) and WATER
• Remember carbon monoxide is
POISONOUS
Carbon monoxide is colourless, odourless and
poisonous gas and is very dangerous.
Every year people are killed while they sleep due to a
faulty gas fire or boiler filling the room with the
deadly gas.
Therefore it is very important to regularly service gas
appliances
Advantages of complete combustion over
incomplete combustion are
• Less soot made
• More heat released
• Poisonous carbon monoxide is not
produced.
CRUDE OIL
Fossil fuels
Coal
Oil
Gas
Fossil fuels are non renewable which means they take a
very long time to make and are used up faster than they
are formed
Crude oil
Dark sticky liquid
Mixture of Hydrocarbons
Hydrocarbon – made of Carbon and Hydrogen ONLY.
Separated by Fractional distillation
Crude oil is found deep within the earth’s CRUST
It needs to be pumped to the earths surface
There are some environmental problems with
extracting crude oil
It can cause oil spills - damage to the wildlife and
beaches
Fires involving crude oil release large amounts a black
smoke into the air
Fractional Distillation
Process that separates liquids because they have different
Boiling Points.
Fractions obtained from crude oil:
Petrol, Diesel, Paraffin, Propane, Bitumen and LPG –
contains propane and butane gases
•
•
Fractions with LOW boiling points exit at top
of column
Fractions with HIGH boiling points exit at
bottom of column
Cracking
• Process that converts large ALKANE
molecules into small more USEFUL ALKENE
molecules
•
Needs a catalyst and a high temperature
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SMELLS
MAKING POLYMERS
Perfumes
• An ESTER can be used as a perfume
• It is made by reacting an ALCOHOL with an ACID.
• Esters can be used as solvents
• A perfume stimulates the OLFACTORY receptors in the
nose
• When stimulated theses receptors send a message to the
brain which you perceive as a smell.
Properties of a perfume
• Must evaporate easily – to reach the nose
• Non toxic – so it does not poison you
• Not react with water – or it may react with sweat
• Not irritate the skin – or it would not be possible to put it on
the skin
• Insoluble in water – so it cannot be easily washed off
Diffusion
• In the gas the particles spread out and move from an area of
high concentration to an area of low concentration.
• This is called DIFFUSION.
• This means the perfume smell can be detected some distance
away from the liquid perfume.
Dissolving
• Substances that dissolve in a liquid are SOLUBLE
• Substances that do not dissolve in a liquid are INSOLUBLE
• A substance that dissolves in a solution is a SOLUTE e.g.
salt
• The liquid that does the dissolving is the SOLVENT e.g.
water
• A SOLUTION is a mixture of a solvent and a solute
Nail Varnish Remover
• Nail varnish is INSOLUBLE in water so cannot be washed
off with water.
• To remove it you need a Solvent such as Propanone.
• Water molecules are not attracted to particles in nail varnish
and do not form a solution. The particles in nail varnish are
more strongly attracted to each other than to water.
• With propanone the particles in nail varnish are more
strongly attracted towards the propanone molecules and
form a solution
Cosmetics
Some cosmetics are made from NATURAL sources
Some cosmetics are SYTHNETIC (made by humans)
Testing
• Some cosmetics are tested on animals
• They must be tested to ensure they are safe to use
Reasons for Testing
To find out:
• How far it goes under the skin surface
• If it irritates the skin
• If it irritates the eye
• Is it carcinogenic ( cause cancer)
• If it causes birth defects
• If it is poisonous
Advantages and Disadvantages of Testing
Advantages – Less need to test on humans
Disadvantage - Not possible to guarantee that a cosmetic will
produce the same side effect in animals as in humans
Hydrocarbon
Compound made up of hydrogen and carbon ONLY
Alkanes
These are SATURATED Hydrocarbons
• Methane
CH4
• Ethane
C2H6
• Propane
C3H8
• Butane
C4H10
• Pentane
C5H12
They contain SINGLE COVALENT
BONDS between CARBON atoms
General formula of CnH2n+2
Alkenes
These are UNSATURATED Hydrocarbons
• Ethene
C2H6
• Propene
C3H8
• Butene
C4H10
They contain DOUBLE COVALENT
BONDS between CARBON atoms
General formula Cn H2n
Test for Unsaturation
• If you react an alkene with BROMINE it
will turn the bromine from brown to
COLOURLESS. This indicates unsaturation.
Polymers
• These are very large molecules
• Molecules in PLASTICS are called
polymers
• Polymers are made when many small
molecules called MONOMERS join
together
• The reaction that makes polymers from
monomers is called POLYMERISATION
Polymerisation
This is the process in which many monomers react
together to give a polymer which requires high
pressure and a catalyst
Poly(ethene)
Poly(propene)
Some uses of Polymers:
Poly(ethene) - Shopping bags
Poly(propene) – ropes carpet fibres
Poly(styrene) – Packaging and insulation
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DESIGNER POLYMERS
PAINTS AND PIGMENTS
Uses of Polymers
Ingredients of paint
 Solvent
 Binding medium
 Pigment
Functions
Functions of a solvent :
Functions of a binding medium :
Functions of a pigment :
Polymers (PLASTICS) are used in PACKAGING and
CLOTHING:
• Polyethene or poly(ethene) is used for plastic
bags
• Polystyrene is used for damage protection in
packaging and for insulation
• Nylon and polyester in clothing
Plastics
 Atoms in plastics are held together by strong
COVALENT bonds
 Plastics that have WEAK intermolecular forces
between polymer molecules have low melting
points and can be stretched easily as the polymer
can slide over one another
 Plastics that have STRONG intermolecular
forces between polymer molecules have high
melting points and cannot be stretched easily and
are rigid
Waterproof and Breathable clothing
Advantages of waterproof clothing
• Do not absorb water
• Do not allow water to pass through to the skin
• Advantages of breathable clothing
• Reduces sweating
Biodegradable
• Many polymers are NON BIODEGRADABLE,
so they will not decay or decompose by bacterial
action
Therefore problems associated with using non
biodegradable polymers are:
• Litter
• Difficult to dispose of
However now chemists are trying to develop
addition polymers that are biodegradable.
Disposal of Polymers
Ways that waste polymers can be disposed of
• Use of land fill sites – but they get filled quickly
wasting valuable land
• Burning of waste polymers – but this makes
toxic gases
• Recycling – but difficult to sort out different
polymers
Nylon and Gore-Tex
• Nylon is tough, lightweight, keeps water out,
keeps UV light out. BUT it does not let water
vapour through so sweat condenses.
• Gore-Tex has all the properties of Nylon but is
Breathable. This means it is a great help to active
outdoor people to cope with perspiration
wetness.
Paint
Paint is a mixture called a colloid
 A colloid is where the particles are mixed and
dispersed with particles of a liquid but are not
dissolved.
 The components of a colloid will not separate
because particles are scattered or dispersed
throughout the mixture and are small enough not
to settle at the bottom.
 Used to decorate or protect surfaces
 Many paints are applied as a thin surface which
dries when the solvent evaporates
 Emulsion paints are water based
Oil Paint
Drying of oil paints involves oxidation of the oil
by oxygen
Oil paints
– Have the pigment dispersed in an oil
– Have a solvent that dissolves oil
Dyes
Used to colour fabrics
Some dyes are natural and other are synthetic
Use of synthetic dyes has increased the number of
colours available to colour fabrics
Thermochromic Paint
Thermochromic pigments change colour when
heated or cooled
Uses
– Warming of a hot cap
– Use in electric kettles
Phosphorescent Pigments
Phosphorescent pigments can glow in the dark
They absorb and store energy and release it as
light over a period of time
They are much safer than alternative radioactive
substances
Examples – use in glow in the dark watches