Chemistry C2

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C2 Chemical Resources

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The Earth's Structure

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The Earth's Structure

The crust is the earth's thin outer layer made of solid rock (0-60km).

The lithosphere includes the crust and the mantle and is made up of tectonic plates.

The mantle is a solid section between the crust and the core,but as you go deeper, the temperatures increase and the solid turns into more of a liquid.

The core is really thick, the inner core being solid and outer being liquid.

Radioactive decay causes a lot of the heat inside the earth, which creates convection currents in the mantle and causes the plates in the lithosphere to move. Tectonic plates are made of rock and float on the mantle. Every year they are moving very slowly and the continents are moving too. Volcanoes and earthquakes often occur where the plates meet.

It is difficult to study the inner structure of the earth, but seismic waves can be used to see the structure. They are produced by earthquakes, but can also be produced by man made explosions. By measuring the time it takes for the wave to travel through the earth and where it comes out scientists can draw conclusions about the structure. P-waves can travel through solids and liquids but S-waves only solids.

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Plate Tectonics

For years, fossils of very similar plants and animals had been found on opposite sides of the Atlantic Ocean. Most people thought there used to be land bridges which had sunk or been covered by water. In 1914 Wegener proposed a theory that Africa and South America had previously been joined. He started to look for more evidence to back up his theory and found it e.g. there was matching layers of rocks on both continents. According to Wegener's continental drift theory, about 300 million years ago all of the continents were joined and he called this one 'super-continent' Pangaea.

His theory was not accepted at first because his theory of how the drifting happened wasn't very convincing. However, eventually the evidence became overwhelming. In the 1960s evidence was found that the sea floor is spreading and this along with other evidence was convincing enough to provve Wegener's theory.

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Volcanic Eruptions

Volcanoes occur when molten rock (magma) from the mantle emerges through the earth's crust erupts as lave to the surface. The oceanic crust is denser than the continental crust and when these two plates collide, the oceanic plate is forced under the continental one. This is called subduction and as the oceanic crust is forced down, it melts and forms magma.

When the molten rock cools down and solidifies, igneous rock is formed. The type of igneous rock and behaviour of the volcano depends on how quickly the magma cools and the composition of the magma. Some volcanoes produce magma which is iron rich basalt. This produces runny lava and he eruption is fairly safe. But if the magma is silica-rich rhyolite, the eruption is explosive and thick lava is produced which can be violently blown out of the top of the volcano.

Geologists can try to predict when volcanoes are going to explode by monitoring things like magma movement. Being able to spot these signs means that scientists can predict eruptions with much greater accuracy than in previous years. 

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Sedimentary Rock

Sedimentary rock:

Sedimentary rocks are formed from layers of sediment laid down in lakes or seas. Over a long period of time the layers get buried under more layers and the weigt squeezes out the water. Fluids flowing through the pores deposit natural mineral cement.

Limestone is a sedimentary rock and is mostly formed from sea shells. When limestone is heated it undergoes thermal decomposition to make calcium oxide and carbon dioxide.

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Metamorphic and Igneous

Metamorphic rocks

Metamorphic rocks are made of other rocks, and formed under heat and pressure over many years. The mineral structure and  texture can be different, but the chemical composition is often the same.

Marble is an example of a metamorphic rock and is another form of calium carbonate. Very high temperatures and pressures bereak down the limestone and it reforms as small crystals which gives the marble a more even texture and makes it much harder.

Igneous rocks

Igneous rock is formed when magma cools. They contain various different minerals and interlocking, radomly arranged crystals which makes them extremely hard. 

Granite is a good example of igneous rock and it is even harder than marble. This makes it ideal for things like steps and buildings.

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Construction Materials

Rocks tend to be a mixture of minerals, ores are rocks in which we can get useful materials from. Aluminium and iron are useful construction materials which can be extracted from their ores.

Glass is made by melting limestone, sand and sodium carbonate and when it cools it forms glass.

Bricks are made from clay. Weathered and decomposed rocks form clay. It's soft and easy to mold into bricks, and can be hardened by heating them to extreme temperatures. This makes them ideal for building as a brick can withstand the weight of lots more bricks.

Cement is made from limestone and clay. When cement is mixed with water a chemical reaction takes place slowly which causes the cement to go hard. Sand, gravel and water can be mixed in with the cement to make concrete. Concrete is a very quick and cheap way to construct buildings, but not very vicually pleasing. Reinforced concrete is a composite material made of concrete and a steel support. It is a better construction material than ordinary concrete because it cinnbines the hardness of concrete with the flexibility and strength of steel.

Extracting rocks can cause environmentla issues though as quarrying uses up land and destroys habitats. Transporting rock can be can noise and pollution and the quarrying process itself produces a lot of dust and noise. Disused sites can be dangerous as people can drown in former quarries that have been turned into lakes.

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Extracting pure copper

Electrolysis is used to obtain very pure copper.The copper is in a liquid called the electrolyte which conducts electricity. Ellectrolytes are usually free ions disolved in water and in purifying copper, Copper (II) sulfate solution is the electrolyte used. The electricl supply acts sort of like an elecrtical pump: 1. it pulls electrons off copper atoms at the anode causing them to go into the solution as Cu2+ ions  2. it then gives the electrons to Cu2+ ions at the cathode to turn them back into copper atoms 3. the impurities are dropped at the anode as sludge and pure copper atoms bond to the cathode. Recycling copper is better than using new copper because it is cheaper, saves resources and uses less energy.

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Alloys

An alloy is a mixture of metal and other elements or a mixture of two or metals. Often alloys have properties from all of the materials they are made from, which can make them more useful than the pure metal. 

Steel is an alloy of carbon and iron. Steel is harder than iron and alsoo stronger. Iron on its own will rust (corrode) fairly quickly, but steel is much less likely to rust. A lot of things are made of steel such as girders, bridges, cutlery and drill bits.

Brass, bronze, solder and amalgam are also alloys, brass being an alloy of copper and zinc. Most of the properties of brass are a mixture of copper and zinc, but it is much harder than either of them. It is used for making musical instruments and also for fittings and fixtures, e.g. screws, spprings and doorknobs. Bronze is an alloy of copper and tin. It is much harder and stronger than copper or tin and is also more resistant to corrosion. It's also used springs and motor bearings, and also for things such as bells and sculptures. Solder is an alloy of tin and lead, it doesn't have a specific melting point but gradually solidifies as it cools. Useful for soldering things together. Amalgan is an alloy cointaining mercury. It is used for filings. 

Some alloys are smart such as nitinol, made of nickel and titanium. It has shape memory so can go back to its original form. You can get glasses with nitinol frames so they can be bent and go back to how they were.

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Building Cars

Iron and steel corrode much more quickly than aluminium. Rusting can only occur when the metal comes into contact with both oxygen and water. The chemical reaction that takes place is an oxidation reaction, the iron gains oxygen too form iron (III) oxide. Water then becomes losely bonded to the iron (III) oxide and the result is hydrated iron (III) oxide which is what we call rust: iron + oxygen + water --> hydrated iron (III) oxide. Unfortunately, rust is really soft and crumbly so it can easily flake off and leave more iron that is available to corrode. Also, if the water is salty or acidic it happpens much quicker.

Aluminium doesn't corrode when it's wet, because it reacts ery quickly with oxygen in the air to form aluminium oxide. A protective layer of aluminium oxide sticks to the aluminium and stops any other reaction from taking place.

Car bodies

Aluminium has two big advantages over steel, one being the factvthat it corrodes less so has a longer lifetime. Also, it has a much lower density so it will be lighter and gives the car better fuel economy. But it has a massive disadvantage: it costs a lot more than iron oor steel.

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Building Cars

You need various materials in cars:

  • Steel is strong and can be hammered into sheets and welded together - good for bodywork.
  • Aluminium is strong with a low density so is used to reduce weight in parts of the engine.
  • Glass is transparent so is needed for the windshield and windows.
  • Plastics are light and hardwearing - used for internal coverings for doors, dashboards and electrical insulators and electrical wires.
  • Fibres (natural and synthetiic) are hardwearing so used for seat and the floor.

Recycling Cars:

Recycling cars is important because it saves natural resources, saves money, and reduces landfill use. A lot of metal is recycled from a scrap car, but other materials (plastics, rubber, etc.) go into landfill. But Europeans laws are now in place saying that 85% of materials in cars must be recyclable. The biggest problem with this is that the materials must be separated before being recycled.

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pH Scale

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A very strong acid has a pH of 0 and a very string alkali has a pH of 14. A neutral substance has a pH of 7.

The dye in an indicator changes colour depending on the pH. Universal indicator is a combination of dyes and changes colour acording to the pH scale. Some indicators e.g. phenolphthalein change colour suddenly at a particular pH e.g. colourless to bright pink.

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Acids and Bases

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An acid has a pH of lower than 7, and form H+ ions in water, the pH being determined by the concentration of H+ ions. A base is a substance with a pH greater than 7. An alkali is a base soluble in water and alkalis foorm OH- ions in water. The reaction between acids and bases is called neutralisation: acid + base --> salt + water. In terms of ions: H+ + OH- <--> H2O (the symbol means it is reversible). the products of this reaction are neutral.

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Reactions of Acids

Metal oxides and hydroxides are bases but some dissolve in water so are alkalis. Evem bases that don't dissolve in water still react with acids to form a salt and a water. Acid + Metal Oxide or Hydroxide --> Salt + Water.

hydrochloric acid + copper oxide --> copper chloride + water

sulfuric acid + potassium hydroxide --> potassium sulfate + water

nitric acid + sodium hydroxide --> sodium nitrate + water

phosphoric acid + sodium hydroxide --> sodium phosphate + water

Acids and carbonates produce carbon dioxide: acid + carbonate --> salt + water + carbon dioxide.

hydrochloric acid + sodium carbonate --> sodium chloride + water + carbon dioxide

sulfuric acid + calcium carbonate --> calcium sulfate + water + carbon dioxide

phosphoric acid + sodium carbonate --> sodium phosphate + water + carbon dioxide

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Reactions of Acids

Acids and ammonia produce ammonium salts:

Acid + Ammonia --> Ammonium salt

hydrochloric acid + ammonia --> ammonium chloride

sulfuric acid + ammonia --> ammonium sulfate

nitric acid + ammonia --> ammonium nirate

This last equation goes to make the famous ammonium nitrate fertiliser.

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Fertilisers

The three main essential elements in fertilisers are nitrogen, phosphorus and pottasium, without these plants cannot grow well and their life processes are affected. the elements may be missing from soil if they have previoously been used up, fertilisers replace these missing elements and provide more of them which helps to increase crop yield as the crops can grow faster and bigger. But before they can be taken in by crop roots they must be dissolved in water.

Ammonia can be neutralised with acids to produce fertilisers. If you neutralise nitric acid with ammonia you get ammonium nitrate. Ammonium sulfate is made by sulfuric acid and ammonia, ammonium phosphate is made using phosphoric acid and ammonia, potassium nitrate is made using nitric acid and potassium hydroxide. All of these are examples of fertilisers.

Fertilisers are really useful but can cause problems. The population of the world is rising quickly and fertilisers increase crop yield. Therefore, the more fertilisers we make and use, the more crops we can grow and the more people we can feed. But using too many fertilisers can risk polluting water supplies and causing eutrophication.

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Eutrophication

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Preparing Fertilisers

Preparing ammonium nitrate

You can make most fertilisers using the titration method. To make ammonium nitrate you need ammonia and nitric acid. 1. You would have the acid in the burette and ammonia and methyl orange in a conical flask. 2. Then add the nitric acid slowly, swirling all the time. The mixture should turn from orange to red when all of the ammoina has been neutralised to make ammonium nitrate solution. 3. To get solid ammonium nitratte you would evaporate most of the liquid, only leaving little and then leaving it to crystalise. 4. But these are not pure as they have some methyl orange in them so you have to note exactly how much acid was needed and repeat without using the methyl orannge.

Percentage yield

Percentage yield compares the actual yield to the predicted yield (yield just being the mass of the product you end up with). You never get 100% yield but the higher percentage you get, the more product you will have ade and the less you have wasted.

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The Haber Process

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Nitrogen is obtained easily from the air (78% nitrogen in air). Hydrogen comes from the cracking of oil fractions or natural gas. Because the reaction is reversible not all of the nitrogen and hydrogen will be converted to ammonia, they don't react soo can be recycled and passed through again so nothing is wasted. Industrial conditions are a high pressure (200 atmospheres), 450 degrees C temperature and an iron catalyst.

The high pressure and low temperatures increase percentage yield. However, lower temperautes slow down the reaction rate so manufacturers tend to use high temperatures anyway to increase the reaction rate. 450 degrees Celsius is the optimum temperature as it gives a fast reaction rate with a reasonable percentage yield. The unused nitrogen and hydrogen are recycled to reduce waste.

The iron catalyst speeds up the reaction and keeps cost down. Without the catalyst the temperatures would have to be even higher to get a quick enough reaction, which would reduce the perecentage yield further, so the catalyst is important.

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The Haber Process

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Minimising the cost of production

1. Price of energy: industry needs to keep its energy bills low, but higher temperatures increase the running costs.

2. Cost of raw materials: this can be kept to a minimum by recycling any materials that haven't reacted. The Haber process is a good example of this.

3. Labour/wages cost: you have to pay your workers money, and labour intensive processes can be very expensive. Automation cuts running costs by reducing the number of people involved, but the initial and running cost of machinery can be more than the cost of their wage bills.

4. Equipment costs: the cost of the equipment depends on the conditions it has to cope with. For example equipment that has to cope with extreme pressures would be very costly.

5. Rate of production: generally, the faster the reaction, the lower the costs of production, so rates of reaction are often increased by using a catalyst.

Optimum conditions are chosen to give the lowest production cost per kg of product. However, the rate of reaction and percentage yield must both be high enough to make sufficient amount of product each day. A low percentage yield is okay as long as the starting materials can be recycled.

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Salt

Salt is mined from underground. Rock salt is a mixture of salt and impurities, it's drilled, blasted and dug out using machinery or hot water is pumped into the ground and it dissolves in this to form a salt solution (solution mining). Subsidence can ocur if the holes arre not filled in. This is when the land collapses and slides into the holes. It can be used in this form to stop ice forming on roads or it can be separated out to use in food or making chemicals.

Half equations of the electrolysis of brine

At the cathode 2H+   +   2e- --> H2

At the anode 2Cl-   -   2e- --> Cl2

The electrolysis of brine is done using the Chlor-alkali process. the products of this process are used for all kinds of things. For example the hydrogen gas is used for the Haber process to make ammonia and in margerine. The chlorine is used to disinfect water, to make plastics (e.g. PVC), solvents, or hydrochloric acid. The sodium hydroxide is used to make soap, or can be reacted with chlorine to make household bleach. 

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Electrolysis of Brine

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