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  • Created by: Dr Afzal
  • Created on: 19-04-10 17:41

Cracking Crude Oil (Splitting up long chain hydroc

Long-Chain hydrocarbons form floopy liquids like tar which arn't useful,

so break you break up longer molecules from fractional distillation- Some products are useful like fuels

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You crack (break molecules) by heating them

1) First step is to heat the long chain hydrocarbons to turn it into gas

2) Then the gas (vapour) is passed over a catalyst

3) Aluminium oxide is the catalyst used

4) The long-chain molecules split apart or "crack" on the surface of the of catalyst

5) Most of products = Alkanes + Alkenes

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Alkenes are hydrocarbons which have a double bond between two of the carbon atoms

They are known as unsaturated because they can make more bonds- The double bond can open up

1st three alkenes= ethene, propene, butene

All alkenes have the formula= Cn H2n

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Ethene to Ethanol

Ethene will react with steam to make ethanol

The reactions needs a temperature of 300 c and a pressure of 70 atmospheres

Phosphoric acid is used as catalyst

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Using Alkenes to make Polymers

Polymerisation- (joining together small akene molecules (monomers) to form very large molecules)- Polymers

E.g. Many ethene molecules can be joined up to produce polythene

Monomers have double bonds

Polymers don't have double bonds

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Polymer Physical Properties

The physical properties of a polymer depend on what it's made from

E.g Temperature and pressure of polymerisation-

Polyethene made at 200 c (temp) and 2000 atmospheres is flexible and has a low density

But polyethene made at 60 c (temp) and a few atmosphere pressure with a catalyst is rigid and dense


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Polymer Uses

Light and stretchable polymers (polythene)- Plastic bags

Waterproof coatings for fabrics are made from polymers

Dental polymers are used in tooth fillings

Polymer hydrogel wound dressings keep wound moist

Memory foam- Polymer material that gets softer as it gets warmer

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Plants and Oils

Some fruits and seeds contains a lot of oil, these oils can be extracted and used for food or for fuel

To get the oil out the plant material is crushed

Then you have to press the crused plant material between metal plates and squash the oil out

Oil seperated by a centrifugue

Distillation refines oil

Vegetable oil provides a lot of energy, contains vitamin E and contain fatty acids- Needs for metabolic processes

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You can mix oil with water to make an emulsion- emulsions made up of lots of droplets

Emulsions are thicker than either oil and water

The physical properties of emulsions made them suited to lots of uses in foods

The more oil the more thik the emulsion is

Emulsions also have non food uses- moisturising lotions

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Vegetable Oils can be used to Produce Fuels

Vegetable Oils provide a lot of energy- Sutiable for fuel

Useful fuel made from vegetable oils -Biodiesel (renewable fuel)

Biodiesel produce much less sulfur dioxide pollution than engines burning diesel or petrol

Biodiesel is biodegradable and less toxic than normal diesel

Biodiesel engines release the same amount of carbon dioxide as ordinary diesel engines

Biodiesel comes from plants but normal diesel comes from crude oil

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Using Plant Oils

Oils and fats are either saturated or unsaturated- Contain long chain molecules with lots of carbon atoms

Unsaturated oils contain double bonds between some of the Carbon atoms in their carbon chains

C=C double bonds can be detected by reacting with bromine or iodine

Unstaturated oil decolourise bromine water or iodine water

Monosaturated fats contain one C=C double bond some where in their carbon chains, polyunsaturated fats contain more than one C=C double bond

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Unsaturated Oils can be Saturated

Unsaturated Vegetable oils are liquid at room temperature

Can be hardened by reacting them with hydrogen in presence of a nickel catalyst at about 60 c- CALLED HYDROGENATION

Hydrogen reacts with the double bonded carbons and opens out the double bonds

Hydrogenated Oils have higher melting points than unsaturated oils

Partially hydrogenating vegetable oil means end up trans fats- very bad for you

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Vegetable Oils in Foods can affect Health

Vegetable oils tend to be unsaturated, while tend to be saturated

Saturated fats increase the amount of cholesterol in blood which can block up arteries and increase risk of heart disease

Natural unsaturated fats such as olive oil and sunflower oil reduce the amount of blood cholesterol

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Food Additives

Food manufacturers add various chemical compounds to improve its appearence, taste etc- ADDITIVES

Additives in UK have "E" numbers, e.g. E127

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Artificial can be detected by Chromotography

1) Extract colour from each food sample by placing in it a small cup with few drops of solvent

2) Put spots of each coloured solution on a pencil baseline on filter paper

3) Roll up the sheet and put it in a beaker with some solvent

4) The solvent seeps up the paper, taking the food dyes with it. different dyes form different spots in different places

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Food Additives- Benefits and Drawbacks

Preservatives- help food stay fresh

Colourings and Flavourings- make food look and taste better

Emulsifiers and stabilisers- stop emulsions like mayonaise from spreading out

Sweeteners- can replace sugar in some processed foods- helpful to diabetics and dieters

Some synthetic additives are identical to natural substances

Some additives are of natural origin e.g lecithin from soya beans

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Continental Drift

Alfred Wegner came across some work listing the fossils of very similar plants and animals which had been found on opposites sides of the Atlantic Ocean

But Wegner also noticed that the coastlines of Africa and South America seemed to join together like a jigsaw

Fossil's had been found un wrong places

Wengner said that about 300 million years ago, there had been one supercontinent. This Landmass, Pangaea broke into smaller chunks which moved apart and are still moving

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