chemistry topic 4 revision

Chemistry topic 4 revision

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  • Created by: jesper
  • Created on: 06-04-12 08:06

Crude oil, Fossil fuels and hydrocarbons

Crude oil is formed from dead animals and plants these are called fossil fuels which are buried underground where there is a high temperature and pressure to form in to crude oil. To become crude oil it takes a million years. Crude oils consist of mixed hydrocarbons. The seven main fractions of crude oil are bitumen(for roads and roofs), fuel oil(ships and power stations), diesel oil(cars, lorries and buses), kerosene(aircraft), naphtha(making chemicals), gasoline(cars), bottled gas(refinery gas).

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Hydrocarbons and its properties, when changing the

Hydrocarbons are long chain molecules of hydrogen and carbon
and are made of compounds of hydrogen and carbon only. length the less Properties: When the boiling point increases the length of the molecules increases. The longer the flammable it is. The longer the length more viscous (does not flow easily). The longer the chain the less it evaporates. 

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Complete and incomplete combustion

Complete combustion is:
Hydrocarbon + Oxygen
à Carbon Dioxide + Water Vapour
The flame that is given out in complete combustion is clear blue.
Incomplete combustion:
Hydrocarbon + Oxygen
à Carbon Dioxide + Water + Carbon Monoxide
Incomplete combustion is dangerous because it gives out a colorless, odorless and poisons gas.  The flame that is given out is smoky yellowish. 

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Cracking

Cracking is when long chain hydrocarbons are being split apart into smaller hydrocarbons.  They are split into extra alkenes which can be used to make useful products like plastic. For example when diesel is cracked to make petrol, paraffin and ethane for plastic. Vaporized hydrocarbons are passed over a powder aluminum oxide(catalyst) for 700 degrees Celsius. Long chains are split or cracked this way. Alkanes have single bonds and alkenes have double bonds.

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Alkanes

first four alkanes

  • methane
  • ethane
  • propane
  • butane

all alkanes have the formula CnH2n+2
Since they are single carbons they do not have any spare bonds left that is why they are called saturated hydrocarbons. They won’t form polymers. They burn cleanly I.E. there is complete combustion so they produce Co2 and H2O. As they don’t have spare bonds they don’t change colour.

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Alkenes

First three alkenes

  • ethane
  • propene
  • butane

Since they are double bond carbons, they have spare carbons that is why they are called unsaturated hydrocarbons. Because of their double bonds alkenes are very reactive. 

Polymers are alkenes when they open up there double bond. When alkenes are given some pressure using a catalyst to smaller alkenes. They join hands together to make a long chain. Ethene has two carbons pressure and catalysts are given to ethane so they split up and make a long single chain they are called polyethene. They are called monomers. Propene will become polypropene. Polymers a re plastic. 

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Disadvantages of polymers as plastic

Disadvantages of polymers as plastic

  • - it is difficult to get rid of plastic
  • - most plastics are non biodegradable (can’t be broken down by micro organisms, that is why they don’t rot)
  • - even when it is buried underground they are still there years later
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Alkanes and alkenes and catalyst converters

Alkanes saturated

Alkenes unsaturated

When fuel is burned in the air it mixes with the nitrogen which is already present in the air. To form nitrogen monoxide NO. As well as nitrogen dioxide NO2. Nitrogen dioxide is highly toxic and when this reacts with water vapour in the air it creates acid rain. Nitrogen monoxide can be reduced by mixing it by carbon monoxide. To reduce this reaction all cars must have a catalyst converter.

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Isomerism and the homologous series

Isomerism can be two alkanes with the same number of hydrocarbons however when the structure is different it is called isomerism. Isomerism have the same number only different arranged.

homologous series belong to alkanes(CnH2n+2) and alkenes (CnH2n) and there general formulas. Each one differs by CH2 (one extra atom). They all have the same chemical type. They go in series because they go up in sequence numbers. They also react in a similar way.

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Need To Know

Need to know:

  • Methane 
  • ethane
  • propane
  • butane
  • pentane

This happens In the presents of sunlight and this is called substitution reaction
Methane + Bromineà Bromomethane + Hydrogen Bromide
Methane + Chlorineà Chloromethane + Hydrogen Chloride

 Bromine water as a test to find out whether it is an alkane or alkene if it decolorizes it is an alkene and if not it is an alkane and stays brown.

When hydrocarbons are under go cracking they split up into small reacting molecules called monomers which then later join op to form a long chain like a necklaces to make a polymer. This can be produced into many plastic products.

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Ethanol

Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer. It's also useful as a fuel. For use in cars and other vehicles, it is usually mixed with petrol.

Structure of ethanol
Ethanol molecules contain carbon, hydrogen and oxygen atoms.

Making ethanol from ethene and steam
Ethanol can be made by reacting ethene (from cracking crude oil fractions) with steam. A catalyst of phosphoric acid is used to ensure a fast reaction.

ethene + steam → ethanol
C2H4 + H2O → C2H5OH

Notice that ethanol is the only product. The process is continuous – as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced. These features make it an efficient process, but there is a problem. Ethene is made from crude oil, which is a non-renewable resource. It cannot be replaced once it is used up and it will run out one day.


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Fermentation

Fermentation
Sugar from plant material is converted into ethanol and carbon dioxide by fermentation. The enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen.

C66H12O6 → 2C2H5OH + 2CO2
Unlike ethene, sugar from plant material is a renewable resource.

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Comments

Megan

Hi,

Slides 6 and 7 were empty, so I have deleted them.

Thank you,

Megan (moderator)

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