Chemistry C2

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Earth Structure

Lithosphere = the outer layer of the Earth which is relatively cold and rigid. It comprises the crust and top part of the mantle. It is made out of tectonic plates which are less dense than the mantle below.

Mantle = the zone between the core and the crust. It is cold and rigid close to the crust but the further you get towards the core, the hotter and softer it becomes.

  • The Earth's core transfers energy, so the temperature of the mantle increases with depth.
  • Convection currents slowly move plates.
  • Oceanic crust is denser than continental crust.
  • When they collide, the oceanic plate goes under the continental plate. This is called subduction.
  • Magma rises up through the Earth's crust because it is less dense than the crust. This can cause volcanoes.
  • Different types of igneous rock are forned from lava.
  • Iron-rich basalt rock comes from runny lava in slower volcanic eruptions.
  • Silica-rich rhyolite rock comes from thick lava in explosive eruptions.
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Construction Materials

Clay = Brick

Limestone+Clay = Cement

Sand = Glass

Sedimentary rock (limestone) - It is made from soft sediments compressed and cemented together. This makes the rock very soft.

Metamorphic rock (marble) - It is formed when limestone is changed by heat and pressure. It is typically composed of an interlocking mosaic of carbonate crystals. Marble is harder than limetone because it has been baked.

Igneous rock (granite) - It is formed when magma cools an solidifies. It is very hard as it has interlocking crystals.

  • Concrete is strong under compression (squashing) but weak under tension (pulling).
  • If a heavy load is applied to a beam, the comcrete will bend, creating tension and compression. The tension cracks the concrete.
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Extracting Copper

Advantages of recycling copper:

  • Has a low melting point so does not cost a lot to melt.
  • It reduces the need for mining, saving reserves and reduces the environmental effect.
  • It reduces the cost of copper.

Disadvantages of recycling copper:

  • It is difficult to seperate from other materials.
  • Less copper is mined so less mining jobs.
  • The seperating process may produce pollution.
  • A lot of copper is thrown away as it is hard to make people recycle it.

The impure copper is the anode, and a sheet of pure copper is used for the cathode:

- The positive anode loses mass as the copper dissolves (loses Cu2+ ions; oxidation)

- The negative cathode gains mass as the pure copper is plated onto it. (gains Cu2+ ions; reduction)

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Rusting and Corrosion

  • Only iron and steel rust. Other materials corrode.
  • Acid rain and salt water accelerate rusting.
  • Rusting is an oxidation reaction because iron reacts with oxygen forming an oxide.
  • The word equation for rusting is:

Iron + Oxygen + Water ----> Hydrated iron(III) oxide

  • Aluminium does not corrode in moist air because it has a protective layer of aluminium oxide which, unlike rust, does not flake off the surface.
  • Different metals corrode at different rates.

(http://www.rsc.org/learn-chemistry/content/filerepository/RES/00/000/434/RES00000434-L.JPG)

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Materials used for Cars

Different materials are used in cars because they have different properties (e.g. aluminium in car bodies because they do not erode and have a low density.

- Alloys are mixtures of elements containing at least one metal, and often have different and more useful properties than other metals they are made from. For example:

  • Steel is harder and stronger than iron.
  • Steel is less likely to corrode than iron.

- Car bodies can be built from aluminium or steel and there are advantages and disadvantages of each. Aluminium is lighter and more resistant to corrosion than steel. However, steel costs less and is stronger.

- A lighter aluminium body means that fuel economy is improved. Because aluminium corrodes slowly, the car body will also last longer.

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Recycling

Advantages of recycling the materials from old cars:

  • less mining saves finite resources needed to make metals.
  • less crude oil is needed to make new plastics.
  • less waste means less landfill.
  • fewer toxic materials, such as lead from batteries, are dumped.

Disadvantages of recycling the materials from old cars:

  • fewer mines are built and fewer mining jobs created.
  • difficult to seperate the different materials.
  • some seperating techniques produce pollution.
  • some recycling processes are very expensive.

- There are laws which specify that a minimum percentage of all materials used to manufacture cars must be recyclable to hep protect the environment.

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The Haber Process

Nitrogen + hydrogen <===> ammonia

N2 + 3H2 <===> 2NH3

The optimum conditions for the Haber process are to:

  • use a catalyst made of iron.
  • raise the temperature to about 450oC (fairly low for a industrial process).
  • use high pressure (about 200 atmospheres/20 MPa).
  • recycle any unreacted nitrogen and hydrogen.

- The conditions used in the Haber process are designed to make the process as efficient as possible.

- The optimum temperature is around 450oC. Although the yield is not very high, the rate is fairly quick. This is the best compromise or 'best of a bad balance'.

- Costs increase when the pressure is raised and when the temperature is increased.

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Acids and Bases

- Metal oxides and metal hydroxides are bases

- Neutralisation takes place when an acid and a base react to make salt and water. The word equation for neutralisation is:

Acid + Base ===> Salt + Water

- In solution, all acids contain H+ ions. The pH of an acid is determined by the concentration of H+ ions.

- The higher the concentration, the lower the pH.

- Neutralisation leaves no free H+ ions.

  • Alkalis contain OH- ions (hydroxide ions)
  • Acids contain H+ ions (hydrogen ions)
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Eutrophication

Stages of eutrophication:

1. fertilisers are washed off land into rivers.

2. fertilisers in the water increase the nitrate and phosphate levels in water.

3. this leads to algae growing quickly on the surface (algal bloom).

4. the algae block off sunlight to other oxygen producing plants under the surface which then die.

5. aerobic bacteria use up the oxygen in the water and feed on the dead and decaying plants and the bottom.

6. most living organisms die.

Excessive use of fertilisers can also pollute water supplies.

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Salts

Acids react with bases and metal carbonates to from salts.

The word equation for making salt are:

acid + base ===> salt + water

acid + metal carbonate ===> salt + water + carbon doixide

Some common chemical equations for the neutralisation of acids by a base or metal carbonate can be constructed using:

  • sulfuric acid, nitric acid and hydrochloric acid.
  • ammonia, potassium hydroxide, sodium hydroxide and copper oxide.
  • sodium carbonate and calcium carbonate.

The word equation for the reaction between hydrochloric acid and copper carbonate is:

Hydrochloric acid + copper carbonate ==> copper chloride + water + carbon doixide

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Electrolysis

- Concentrated sodium chloride solution (brine) can be separated by electrolysis.

- Hydrogen is made at the negative cathode.

- Chlorine is made at the positive anode.

During electrolysis of NaCl solution:

  • Na+ and H+ ions migrate to the negative cathode.
  • Cl- and OH- ions migrate to the positive anode.
  • At the cathode, hydrogen is made and electrons are gained (reduction)
  • At the anode, chlorine is made but electrons are lost (oxidation)
  • The ions not discharged make sodium hydroxide solution

Na+ + OH- ===> NaOH

Sodium chloride is an important raw material, obtained by mining it from the ground or by solution mining.

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