Chemistry science a


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  • Created by: leena
  • Created on: 06-06-12 22:10

structure of the earth

earth is almost pherical

diameter 12800km

surface thin,sod crust

crust is a very thin layer that varies in thickness between 5km and 70km 

the mantle is under the crust and is about 3000km thick 

half way through the center of the earth

almost entirly solid but parts of it can flow very slowly

core is about half the diameter of the earth

high proportion of magnetic metals iron and nickel

it has a liquid outer patrt and a solid inner part

earths imited resources come from its crust the ocenas and the atmosphere

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the restless earth

the earths crust and upper mantle is cracked into tectionic plates which are constantly moving

the tectonic plates move because of convection currents in the mante that are caused by radioactive decay

earthquakes and vocanoes happen where tectionic plates meet but its diffuiclt to predict accuratelt when and where will happen because scientists still dont know enough about whats happening inside the earth

wegeners theory of continenta drift was not accepted for many years as he could not expain why the continents moved. instead they belived the earth was shrinking as it cooled.  

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the earths atmosphere in the past

in the first billion years the surface was covered with volcanoes that released carbon dioxide, water vapor and nitrogen

as the earth cooled most of the water vapor condensed to form the oceans. so it was mainly carbon dioxide with some water vapor however some scients thought there was also nitrogen and possiby some methane and ammonia

next 2 billion years bacteria,agae and plants evolved. 

algae and pants used carbon dioxide for photosynthesis and this released oxygen

as the number of plants increased the amount of carbon dioxide decreased and the amount of oxygen increased

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extracting vegtable oil

some seeds,nuts and fruits are rich in vegetable oils.

extracted by crushing and pressing the plant material followed by removing water and other impurities.

some oils are extracted by distilling the plant material mixed with water. this produces a mixture of oil and water from which the oil can be separated 

when eaten, vegtable oils provide us with a ot of energy and important nutrients

can be used as fuels

they are used to make biofuels such as biodiesel

unsaturated oils contain carbon -carbon double bounds (C=C) and so they decolourise bromine water from orange to coourless

if there are several double bonds in each molecule they are called polyunsaturated

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cooking with vegtable oils

useful in cooking because of there high boiling points

cooking in oil increases the energy content of foods and changes the flavor,colour and texture of the food

vegetable oils can be hardened this is called hydrogenation and is done at 60degrees using a nickle catalyst.

the hydrogenated oils have higher meting points because they are more saturated.

this reaction is also called hardening because the hydrogenated oils are solids at room temperature. suitable for spreading

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everyday emulsions

oil and water do not mix and usually separate from each other forming two layers

if we shake it the liquids together tiny droplets form that can be to separate. this type of mixture is called an emulsion

emulsions are opaque and ticker than oil and water are formed

the improve their texture,appearance and ability to coat and stick to soilds

emulsifiers stop oil and water from separating into layers

emulsifiers molecules have a small hydrophilic part and a long hydrophobic parts

hydrophillic parts (head) is attracted to water 

hydrophobic (tail) is attracted to oil

tail part of many emulsifiers molecules go into each oil droplet and so the droplets become surrounded by the head parts this keeps the droplet apart in the water preventing them from joining together and separting out

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food issues

veg oils are high in energy and provide nutrients

vegetable oils are believed to be better for health than saturated fats

veg oils are belived to be better for health than saturated fats

emulsifiers improve texture of foods enabling water and oil to mix therefore this makes fatty foods more palatable and tempting to eat

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