chemistry
all topics
- Created by: niki
- Created on: 03-04-11 12:09
>we can split large hydrocarbon molecules up into smaller molecules by heating them and passing the gas over a catalyst
>cracking produces unsaturated hydrocarbons, which we call alkenes
>alkenes burn, and also react with bromine water producing colourless products
cracking hydrocarbons
> plastics are made of polymers
> polymers are large molecules made when monomers (small molecules) join together
making polymers from alkenes
> monomers affect the properties of the polymers that they produce
> changing reaction conditions can also change the type of polymer that is produced
the properties of plastics
> new polymers are being developed all the time. They are designed to have properties that make them specially suited for certain uses
> smart polymers may have their properties changed by light, temperature or other changes in their surroundings
new and useful polymers
> vegetable oils can be extracted from plants by pressing or distilation
> vegetable oils are important foods
> unsaturated oils contain carbon-carbon double bonds. We can detect them using bromine or iodine solution
extracting vegetable oils
> vegetable oils are useful in cooking because of their high boiling points
> vegetable oils are hardened by reacting them with hydrogen to increase their boiling and melting points (hydrogenation)
cooking with vegetable oils
> oils do not dissolve in water
> oils can be used to produce emulsions which have special properties
> emulsions made from vegetable oils are used in many foods, such as salad dressings and ice creams
everyday emulsions
> additives may be added to food in order to improve it's appearance, taste and how long it will keep (it's shelf life)
>food scientist can analyse foods to identify additives
what is added to our food
e numbers
> vegetable oils can be burned as fuels
> vegetable oils are a renewable source of energy that could be used to replace some fossil fuels
vegetable oils as fuels
> the earth consists of a series of layers
- crust
- mantle
- outer core
- inner core
- centre of the earth
> scientists orignally thought that the features on the Earth's surface were caused as the crust cooled and shrank
structure of the earth
> the earth's lithosphere is cracked into a number of pieces (tectonic plates) which are constantly moving. Where these plates meet, earthquakes and volcanoes happen
> the motion of the tectonic plates is caused by convection currents in the mantle, due to radioactive decay
> earthquakes and volcanoes happen where tectonic plates meet. It is difficult to predict accurately when and where earthquakes will happen
the restless earth
> the earth's early atmosphere was formed by volcanic activity
> it probably consisted mainly of carbon dioxide. There may also have been water vapour together with traces of methane and ammonia
> as plants colonised the earth, the levels of oxygen in the atmosphere rose
the earth's atmosphere in the past
> the main gases in the earth's atmosphere are oxygen and nitrogen
> about four-fifths (4/5) (80%) of the atmospher is nitrogen and one-fifth (1/5) (20%) is oxygen
> the noble gases are unreactive gases found in group 0 of the periodic table. Their lack of reactivity makes them useful in many ways
> noble gases are helium, argon, neon, kyrpton, xenon and radon
gases in the atosphere
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