Science 1.5-1.7

Dual Award Science revision cards for the  second part of unit 1

  • Created by: Penny
  • Created on: 12-06-12 17:05


What is Cracking?

Cracking is the process used to break up large oil molecules into smaller, more usable alkanes and alkenes.

Why do we use Cracking?

Fractional distillation seperates crude oil into sections with roughly the same sized molecules. However, there is much greater demand for hydrocarbons made up of small molcules so cracking allows us to fill this demand.

What happens in the Cracking Process?

Firstly, the liquid hydrocarbons are vaporised by heating and mixed with a hot catalyst, this speeds up the reaction.

Cracking will then break the long alkane molecules into a mixture of shorter alkanes and alkenes.

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Cracking 2


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What are Alkenes?

Alkenes are a type of hydrocarbon, their general formula is CnH2n (where n represents a numerical value). All alkenes will have a carbon-carbon double bond but every carbon atom will still have four bonds in total. These double bonds make alkenes far more reactive than alkanes, this makes them more reactive than alkanes. To detect these double bonds bromine water should be added to the compound which is desired to be sampled, if it becomes colourless then there is one or more double bonds in the solutions.

Examples Of Alkenes:

Ethene- C2H4                         Hexene- C6H12                                      

Propene-C3H6                        Heptene- C7H14

Butene- C4H8                         Octene- C8H16

Pentene- C5H10                     Nonene- C9H18

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What are Polymers:

Polymers are molecules consisting of very long chains made from carbon atoms with other atoms attatched. 


Plastics are usually made from alkenes. A polymer molecule will contain practically up to 1 million atoms joined together, polymerisation is the process that forms monomers into polymers. 


The monomer will be heated under pressure and the chain reaction that occurs next will be triggered by a catalyst, it will make a C=C double bond open up and join onto the next monomer and so on so an atom will go from being C=C to C-C-C and so on, with the hydrodgen (or other atoms) remaining attatched as before.

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Plant Oils

Types of Vegetable oil:

Examples of vegetable oil include: Sunflower, rapeseed, corn, soya, sesame, groundnut,  coconut, almond, olive and palm.

Extraction of Oil:

Fruits, nuts and seeds are crushed to obtain their oils, this pulp is pressed through filters to separate the oil and solids, the solids will then be dissolved in a solvent to remove any remaining oil, and then the oil is separated from the solved by distillation. Essential oils from flowers are extracted using steam distillation. The steam will vaporise the oils and the steam and oil vapours will pass into the condenser where they will become liquid again, the oils will ten float on top of the water. 

Uses of Oils:

Oils can be used in food, cosmetics and as fuel in the form of bio-diesel. 

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Fats (saturated and unsaturated)

Unsaturated fats:

Unsaturated fats contain C=C double bonds (those with two or more are polyunsaturated fats). They have lower melting points than saturated fats and are usually liquids at room temperature. To test for unsaturated fats a small amount of fat is dissolved in ethanol and then mixed with water, bromine water is then mixed in and if the solution goes colourless then the fat is unsaturated, if it remains orange brown then the fat is saturated.

Hydrogenation: Hydrogenation is when hydrogen is bubbled through a mixture of oils and nickel particles at 150c to allow the C=C double bonds in unsaturated fats to 'soak up' the hydrogen and become saturated, making the  fat harder.

Saturated Fats:

Saturated fats only contain C-C single bonds, they are often solid at room temperature. Saturated fats can also increase cholesterol and are therefore considered less healthy than unsaturated fats.

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What are emulsions? Emulsions are a mixture of oil and water. They are made up of droplets of oil suspended in water or water droplets suspended in oil.

How are emulsions Formed? Oil and water normally do not mix, but when they are shaken up the liquids form small molecules which do mix together for a time but will eventually separate as oil is hydrophobic. This can be prevented by using an emulsifier (a substance made up of molecules with both a hydrophobic and hydrophilic ends which binds the oil and water molecules together). The oil droplet will become surrounded by the emulsifier and the hydrophobic ends will connect to the oil molecule with the hydrophilic end remaining in the water to prevent the oil from separating. 

Examples of Emulsions: 


-Ice Cream

-Oil+vinegar salad dressings

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The Earth

Earth's Layers:

- The surface (crust) made up of rock and 70% covered by water

- The mantle, consisting of molten rock

- The middle (core) a very hot mixture of iron and nickel

-The atmosphere- A layer of air and other gases surrounding the earth

Tectonics Plates:

Tectonic plates are the primary feature of Wegener's theory of 'Pangea'- his original name for earth when all the continents were joined. He claimed that the continents were constantly moving apart in a movement called Continental Drift. This theory was backed up by the fact that the continents appear to fit together like a jigsaw puzzle and also by fossils found where the continents would have once been joined. The tectonic plates are in the litosphere which is the semi-solid part of the mantle and the earth's crust, and the movement is caused by convection currents in the mantle. The plates don't only drift apart though, some of them drift closer together, when they collide they push the land upwards, forming mountains. When tectonic parts move apart, magma will come up from the mantle and form new crust, as the magma solidifies it becomes part of the mid-Atlantic ridge.

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The Earth's atmosphere

How did the Earth's Atmosphere Evolve?

In the first 1000 million years there were no oceans, only volcanoes, which released huge volumes of CO2- most of the atmosphere was made up of this with small amounts methane and ammonia also being there.

The volcanoes released steam, which condesed to form rain as the earth cooled forming ocean which some of the CO2 dissolved in.

3400 million years ago the gases in the atmosphere allowed life to develop and these primitive organisms released oxygen into the atmosphere. The oxygen reactive with the ammonia to become nitrogen, bacteria also converted ammonia into nitrogen.

400 million years ago some oxygen was converted into ozone which protected the earth from ultraviolet rays, which allowed plants to grow, their photosynthesis removed more CO2 from the atmosphere and released more oxygen, eventually, the atmosphere balanced out about 200 million years ago- and has remained pretty much the same ever since. 

The Carbon Cycle: Carbon Dioxide is released by respiration, decomposing organisms, burning fuels, carbon in plants and carbon in animals. It is taken in by photosynthesis.

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Adaptations for Survival

What is Adaptation: Adaptation is when a species of plant or animal have features that have developed to allow them to survive best in their environment. A well adapted organism will be able to successfully compete for things necessary for their life and if the species is not able to thrive in a particular habitat it will either die out or move elsewhere.

Examples of Adaptation:

A plant that lives in a dry place will have long, wide spreading roots that grow deep into the soil and an animal may have the ability to survive without much water.

An animal that lives in a cold place may have thick layers of fur and fat and be coloured white to camouflage them.

Many plants have special adaptations such as thorns, poisons and warning colours to deter consumers.

Extremophiles: Extremophiles are animals that are adapted to live in usually uninhabitable environments, usually micro-organisms.

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Food Chains and Biomass

What do Food Chains Show?

Food Chains show the flow of energy as it passes from one organism to another. The plant or object at the beginning of the food chain is known as the producer and all the organisms above it are consumers.


Pyramids of biomass show the mass of living material used to support each organism above it. At each level the biomass decreases, for example, not all of the food below will be eaten and some energy will be wasted through the waste materials produced by the animals in the pyramid such as carbon dioxide, urine and faeces. Energy will also be wasted through respiration as energy be will released from consumed nutrients so that the organism can use it for movement and other purposes- much of this energy will eventually be lost as heat in the surroundings/

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Genes, Chromosomes and reproduction

What are Genes and Chromosomes:

Chromosomes store the information needed for survival, there are 46 chromosomes in each human cell. Genes are the information that is in our body which determines characteristics of our appearance, they make up chromosomes. Genes are passed down from our parents, half from each one.

Sexual Reproduction:

Sexual reproduction is when a male and female gamete come together in the process called fertilisation creating a new organism which is a combination of both their genes.

Asexual Reproduction:

Some animals create young by growing them from their body or by splitting into many pieces. The organisms which are then produced have the same genes as their parents.

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What is cloning?

Cloning can be done in two ways. The first is for plants and involves a process called tissue culture, a very small piece of tissue from a parent plant will be grown in a Petri dish containing a jelly with all the nutrients it requires, eventually the tissues will grow into a complete adult plant. It can also be done via cell cloning. The nucleus will be removed from and unfertilised egg cell and another cell will be taken from the body of the animal that is going to be cloned, the nucleus will be taken from it using enzymes and planted into the egg cell. This new egg cell will be given a small electric shock to start the division process and will be placed into a 'surrogate mother' where it will develop into an embryo which is identical to the cloned animal.

Human Clones?

It is considered unethical to clone humans, so it has never been done, but it would be possible. However, natural human clones do exist in the form of identical twins, who have the same genes.

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Genetic Engineering

What is Genetic engineering?

Genetic engineering is the process in which a gene is taken from one organism and put into another to produce a new organism which features the desirable characteristic of the gene from the organism from which it was removed.


- Herbicide Resistant crops- allows farmers to remove weeds without harming the crops

- Bacteria designed to create insulin for those with diabetes

- Fortified Rice- Allows those in third world countries to be supplied with nutrients through the staple food of their diet

Good or Bad?

Yields of crops can be increased and extra nutrients can be incorporated into them, GM can also allow us to produce useful things such as insulin which can benefit human life. However, people are concerned about mutation and potential harmful effects of ingesting crops with Genetic Modification.

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What is Evolution?

Evolution is how things change over time. It is thought that life on earth began as small, single celled organisms which over millions of years gradually evolved to become the life that is on earth today.

Lamarck's Idea:

Jean Baptiste Lamarck suggested that environmental changes in organisms were passed onto their offspring. This idea was wrong.

Darwin's Idea:

Darwin suggested that species gradually changed over time by natural selection. Darwin thought that within each generation only the best adapted individuals would survive and therefore by mating the next generation had these positive traits and this cycle continued gradually causing evolution to occur over time.

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Power Stations

How do power stations work?

Fuel is burned to heat water-> the hot water changes to steam -> the steam drives round a turbine -> steam condenses back into water and is returned to the boiler    -> the turbine turns and in turn makes the generator turn -> generator generates electricity -> the step up transformer increases the voltage to allow the electricity to enter the national grid 

Renewable energy: e.g.- wind power, hydroelectric, tidal power, wind turbines and solar power

Non-renewable energy sources: e.g.- nuclear and fossil fuels. 

National Grid:

Step up transformers = at the start- increases voltage 

Step down transformer= at the end- reduces voltage

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What are waves?

Mechanical waves transfer energy examples of these are sound and literal water waves. Electromagnetic waves also transfer energy, examples of these include, infra-red, visible light and ultraviolet. Mechanical waves require a medium to pass through whereas electromagnetic waves can pass through a vacuum.

Transverse or longitudinal?

Longitudinal waves oscillate in the same direction that the wave travels but transverse waves oscillate at right angles to the direction the wave travels. An example of longitudinal waves is sound waves. All electromagnetic waves are transverse. 

Wavelength and Frequency Relationships (sound wave specific):

The shorter wavelength the higher the frequency and the more energy transferred

The longer the wavelength the lower the frequency and the less energy transferred

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Reflection, Refraction and Diffraction


Reflection allows us to see things, as light reflects off the surface of an object and into our eye. The law of reflection states: when any wave reflects from a surface, the angle at which is reflected is the same as the angle that it strikes the surface.


Diffraction is when a wave passes through a gap or goes round a corner. As a wave passes close to an obstacle the part of the wave nearest it will be curved, a gap is like two obstacles so the wave will curve at each side. Diffraction will be at its greatest when the gap is the same as the wave's wavelength. Light does not diffract much due to its small wavelength, radio waves are easily diffracted as they have long wavelengths.


Refraction is when a wave changes speed when travelling through a different medium.

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The EM spectrum


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Dangers of Radiation

Microwaves from Mobile Phones:

Scientists claim that the microwave radiation can damage the cells in our brain but there is not enough research to prove it.

Electromagnetic Radiation Dangers:

Microwaves can heat up cells, radio waves are harmless, infra-red radiation can burn skin and tissues, visible light can damage eyes, ultraviolet rays can cause sunburn and skin cancer, xrays can burn, damage cells and cause cancer finally, gamma rays can destroy cells and cause cancer.

Examples of Protective methods:

Sun creams contain chemicals that protect our bodies from harmful UV rays, Radiographers sit behind a lead glass screen and patients may wear a lead apron for protection during an x-ray and microwave doors have a very fine mesh in them to prevent the radiation from escaping. 

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The Doppler Effect

What is the Doppler effect?

The Doppler Effect is how a sound wave changes as an object moves towards or away from you.

About the Doppler Effect:

As a sound gets closer to you you hear a sound with a higher frequency and a shorter wavelength than the actual sound being made and as it moves away you hear a sound with a lower frequency and a longer wavelength than the sound being made.

The Doppler Effect and Light:

The doppler effect can usually not be observed with light as it travels too fast, but it is noticable in space. As a light source (e.g. a star) is moving towards us the waves would appear to be bunched together, making the light appear bluer, but if the light source is moving away from us, the waves would be spread out making the light appear redder.

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Red Shift and CMBR

Red Shift:

Red shift shows that all galaxies are moving away from us and that the galaxies further away from us are moving faster than those which are closer. Galaxies further away have a bigger red shift and those closer have a smaller red shift. Discovered by Edwin Hubble.

Will the Universe stop expanding?

No one is able to tell if the universe will ever stop expanding, things move outwards because of the energy that they received from the big bang however gravity also causes them to be attracted towards each other, and if this force is strong enough expansion may eventually be slowed.

Cosmic Microwave Background Radiation:

Cosmic microwave background radiation is the microwave radiation that is everywhere in space. Scientists say that this is left over from the big bang which is the only actual proof for this theory.

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information from: Collins GCSE science A student book

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Thank you, this has covered everything I need to revise for x



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Your Secret Admirer

Conor Murphy


This is brilliant! An essential resource!

lisa linsdell


A good set of revision cards for this unit. suitable for Higher papers. Full definitions of key words and phrases.



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