Chemistry 1-3

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Evolution of the atmosphere

Phase 1- Surface was originally molten for millions of years.

  • So hot everything boiled away into space. Things cooled down and thin crust formed, volcanoes still erupting.
  •  Volcanoes gave out CO2, N2 and water vapour. This is how atmosphere formed. The early atmosphere was mostly C02 and water vapour with virtually no oxygen. 
  • Oceans formed when water baour condensed when the Earth cooled. 

Phase 2- Green plants evovlved and produced oxygen 

  • Greenplants evolved over most of the Earth. Happy in the CO2 atmospher 
  • A lot of early CO2 dissolved into the oceans. The green plants removed CO2 from the air and produced CO2 by photosynthesis. 
  • When plants died they were buried under layers of sediment, the carbon they had removed became locked up in sedimentary rocks

Phase 3-

Build up of O2 killed off early organisms that couldn;t tolerate it. This allowed more complex organisms to evolve. There is virtually no CO2 left now.

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The atmosphere today

Atmosphere is maninly: 

  • 78% Nitrogen 
  • 21% Oxygen 
  • 1% Argon 

Human activity is adding pollutants to the atmosphere. There are five pollutants 

  • Carbon dioxide 
  • Carbon monoxide
  • Particulates
  • Sulfur dioxide
  • Nitrogen oxides 
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Chemical Reactions and Fossil fuels

  • All substances made of atoms 
  • When atoms join together they make molecules 

Fossil Fuels 

  • Fossil fuels are hydrocarbons- contain the elements hydrogen and carbon. 
  • Many hydrocarbons are fossil fuels- formed from the remains of dead plants and animals over millions of years. Drilled from the ground e.g. crude oul and refined to make products like petrol and diesel. 
  • Coal is made mostly from carbon not a hyfrocarbon. 

Burning fuels is an example of oxidation 

  • Combusion is a type of chemical reaction
  • When a hydrocarbon burns. the hydrogen atoms in the fuel combine with oxtgen atoms in the air to make hyfrogen oxide, The carbon atoms in the fuel combine with oxygen atoms in the air to form carbon dioxide. 
  • Reaction oxygen added- oxidation 
  • Oxygen lost- reduction
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Air pollution- Carbon

Carbon dioxide- CO2 will stay in the atmosphere until it's removed.

  • CO2 can be removed from the atmospher naturally. Plants use up the CO2 from the air when they photosynthesise. CO2 also dissolves in rainwater and in seas, lakes and rivers. 
  • Despite these ways of removing CO2 from the atmosphere, the level can still increase if human activity e.g. burning fuels, adds extra CO2 into the atmosphere. 
  • An increased CO2 level increases the greenhouse effect, which is warming up the Earth. This is causing loads of problems e.g.sea level rise. 

Carbon Monoxide -Pollutant

Particulate Carbon 

Particles of carbon are produced when fuels burn incompletely- this is called particulate carbon. If they escape into the atmosphere they just float around eventually they fall back to the ground and deposit themselves as soot. A lot of soot just falls onto buildings making them look dirty. 

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Sulfur and Nitrogen

  • When sulfur dioxide gets into the atmosphere it will stay there until something gets rid of it. 
  • The way sulfur dioxide leaves our atmosphere is in the form of acid rain. 
  • The sulfur dioxide emitted from vehicle engines and power stations reacts with the moisture in clouds, dilute sulfuric acid is formed. 
  • Eventually, much of this acid will fall as acid rain, which is bad news for the environment.
  • Acid rain causes lakes to become acidic, killing plans and animals. It also kills trees and damages buildings and statues made from some kind of stone. 

Nitrogen 

  • Nitrogen monoxide forms when nitrogen and oxygen in the air are exposed to very high temperatures. This happens when fuels are burnt in places like car engines. 
  • Once the nitrogen monoxide is in the air. it will go on to react with more oxygen in the air to form nitrogen dioxide. 
  • As pollutants, nireogen oxides are very similar to sulfur dioxide. When they're formed they usually end up in the atmosphere-which is where they stay until they react with moisture in clouds. This produces a dilute nitric acid which eventually falls to the Earth as acid rain.
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C2- Crude oil

Crude oil is a mixture of hydrocarbons. Hydrocarbons are molecules made from hydrogen and carbon atoms only. These chains are varying lengths. 

As the length of the carbon changes, the properties of the hydrocarbons change. Short-chain molecules have lower boiling points- they are often gases. Long- chain molecules have high boiling points and can be quite viscous (thick and sticky) 

There are two important types of bond in crude oil: 

  • The strong covalent bonds between the carbons and hydorgens within each hydrocarbon molecule 
  • The intermolecular forces of attraction between different hydrocarbon molecules in the mixture. 

When the crude oil mixture is heated, the molecules are supplied witth extra energy. 

The intermolecular forcesbreak a lot more easily in small molecules than they do in bigger molecules. That's because the intermolecular forces of attraction are much stronger between big molecules than they ae between small molecules. 

Even if a big molecule can overcome the forces attracting it to another molecule at a few points the force is still strong enough to hold it in place 

That's why big molecules have higher boiling points than small molecults do- more energy is needed for them to break out a lquid and form a gas.

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C2- Polymerisation

Polymerisation-Loads of small molecules linked together 

  • Plastics are formed when lots of small molecules called monomers join together to make a very long molecule called a polymer.
  • They're usually carbon based
  • Under high pressure many smalle molecules join hands to form long chains called polymers 

There are lots of different types of polymers

  • Strong, rigid poymes such as high density polyethene are used to make plastic milk bottles 
  • Light stretchables polymers such as low density polyethene are used for plastic bags and squeezy bottles. low density polyethene has a low melting point so its no good for anything that'll get very hot. 
  • Heat resistany polymes such as meliamime are used to make plastic kettles 

Polymers have replaced natural materials for some uses 

  • synthetic fibres like nylon and polyester are used to replace cotton, wool or silk fabrics. Its lighter, more durable and cheaper
  • Rigid PVC has replaced wppd as a material for window frames. Its weather resistant, strong and durables
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Structure and properties of polymers

A polymers propertied decide its uses.Its properties depend on how the molecules are arranged and how they're held together. 

Weak forced: Chains held together by weak forces are free to slide over eah other. This means the plastic can be stretched easily, and will have a low melting point

Strong forces: Polymers with stronger bonds  between the polymer chains have a higher melting point and can't be easily stretched, as the crosslinks hold the chains foirmly together. 

Polymers can be modified to give them different properties 

  • Polymers can be modified to increase their chain length. Polymers with short chains are easy to shape and have lower melting points. Longer chain polymers are stiffer and have higher melting points. 
  • Polymers can be made stronger by adding cross-linking agents. These agents chemically bond the chains together, making the pollyment stiffer, stronger and more heat resistant. 
  • Plasticisers can be added to a polymer to make it softer and easier to shape. Plasticisers work by getting in between the polymer chain and reducing the forces between them. 
  • The polymer can be made more crystalline. A crystalline polymer has straight chains with no branshes so the chains can fit close together. Crystaline= higher density, stronger + higher melting point
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Nanotechnology

Nanomaterials are tiny. Nanotechnology is the branch of technology dealing with the making and use of these nanoparticles. SOme of the structures that are dealt with in nanotechnology are only as big as some molecules so nanotechnology involves understanding how to control matter on a very small scale. 

Some nanomaterials occur natuarrly or are produced by accident. For example

  • Seaspray-sea produces nanoscale salt particles which are present in the atmosphere. 
  • Combustion- when fuels are burnt nanoscale soot particles are produced 

Nanoparticles are added to plastics in sports equipment e.g. tennis rackets, gold clubs nad golf balls. They make the plastic much stronger and more durable, and they don;t add weight.

Silver nanoparticles are added to polymer fibres used to make surgical masks. This gives the fibres antibacterial properties.

Although nanoparticles are useful, they way they affect the body is not fully understood. Some people are worried that nanoparticles hace been made available before the effects on human effect are investigated properly.

As the long term effects aren't known, people believe they should be clearly labelled.

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C3- Tectonic Plates

  • Plates don't stay in one place- they move around.
  • Plates move a few cm a year this means that different parts of the world have been located at different positions and are slowly moving away from there current position
  • When tectonic plates move away from each other under the sea the exposed mantle rises up through the seafloor and solidifies to form new crust. 
  • When the new crust is formed it's magnetised by the Earth's magnetic field. Every half million years or so the Earth's magnetic field swaps direction, so the rocks have either normal polority or reversed polarity when they cool 
  • The pattern of normal and reversed polarised rocks can be used to estimate the age of different parts of the Earth's crust and track the very slow movement of the tectonic plates. 
  • Fossils tells you about the age of the rock as well as the conditions under which it was formed. 
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Salt

Salt is left behing by evaporation. In Britian, salt is extracted from underground deposits. These underground deposits were formed when ancient seas containing dissolved salt evaporated. The salt that was left behind was buried and compressed by other layers of sediment over millions of years. Rock salt is a mixture of salt and impurities and is found in underground deposits. It can be extracted by normal mining or by solution mining. 

Normal mining: 

Rock salt is drilled, blasted and dug out and brought to the surface using machinery. Most rrock salt obtained thorugh this mining is used on roads and to enhance the flavour in food. 

Solution mining 

  • In solution mining water is injected into the salt deposit which dissolves the salt to make a saltwater solution called bring. Pressure forces the brine up to the surface through the inner pipe. 
  • The brine is then stored in wells above the surface and pumped to a refining plant. Impurities are removed from the brine in the refining plant and it's then pumped into containers.
  •  The brine is then boiled to make the water evaporate, leaving the salt behind. 

Land above disused mines can collapse into the holes. Mining also needs a lot of energy, which usually comes from burning fossil fuels. 

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Electrolysis of salt solution

Electrolysis causes chemical change- it splits the solution into hydrogen, chlorine and sodium hydroxide. 

Electrolysis of Brine produces three useful products :

  • Chlorine which is used in; disinfectants, killing bacteria , household bleach and insectisides
  • Hydrogenwhich is used to make ammonia, used to change oils into fats and used for welding
  • Sodium hydroxide a very strong alkali which is used to manufacture soap, ceraminc, oven cleaner and house hould bleach 

Large scale electrolysis environmental impact: 

  • Needs a lot of energy. Comes from burning fossil fuels which releases pollutants 
  • Mercury is a tocix chemical used in many brine electrolysis plants. 
  • Asbestos is often used in industrial electrolysis. It can cause lung cancer
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Chlorination

Chlorine is used in water treatment. Driking water is treated to make it safe, Chlorine is an important part of water treatment: 

  • It kills disease- causing microorganisms 
  • If the correct amount is added, enough chlorine remains in the water to kill bacteria that might enter the supply after treatment, 
  • It prevents the growth of algae, gets rid of bad tastes and smells and removed discolouration 

There are disadvantages to chlorinating water: 

Chlorination can have negative impacts on health: 

  • Water contains a variety of organic compunds e.g. from the decomposition of plants. Chlorine reacts with these compounds to form chlorinated hydrocarbons many of which are carcinogenic. However, this increased cancer risk is asmalle compared to the risks from untreated water - a cholera epidemic could kill thousands 
  • Chlorine gas is very harmful if breathed in. Liquuid chlorine on the skin or eyes cause severe chemical burns. Accidents involving chlorine during the chlorination process could be really serious, or fatal.
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Alkalis

An alkali is a compund that forms hydroxide ions when dissolved in water. 

Acid+ Hydroxide= Salt + water

Acid + carbonate= salt + water + carbon dioxide

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Salt in the food industry

There are some health issues with the use of salt

  • Eating too much salt may cause high blood pressure for about 30% of the UK population. High blood pressure can lead to strokes and heart attacks
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