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Most paints have three main parts: - pigment (the coloured part) - binding medium (like a glues, sticks it to the wall) - solvent (thins the paint to make it easier to use) Colloids: Colloids are mixtures of tiny particles dispersed within another, they are NOT DISSOLVED. Paints are colloids, because they have small solid particles of pigment dispersed within binding medium. Pigments: We used to make pigments by grinding down different rocks. Now we use synthetic pigments which are brighter and last for longer. Oil Paint: Oil paint contains pigment, a solvent and oil as the binding medium. Oil paint dries when the solvent evaporates, leaving the oil and pigment. The oil, as the binding medium, dries forming a skin and sticks the pigment to the painted surface. The oil dries by chemical reaction. But the evaporating solvent is also a pollutant.... Manufacturers try to reduce the amount of pollution in their paint. One way to do this is to use emulsion paint. Emulsion Paint: Emulsions contain less solvent. It is basically the same as oil paint, except it is dispersed within water (as oil and water do not mix). Therefore, emulsion paints are colloids in two ways: they have pigment dispersed with oil, and then that oil dispersed in water. When emulsion paint dries, the water evaporates leaving the oil droplets behind, which join together to make a continuous film. Thermochromic Paints: These paints change colour at certain temperature. They normally change from coloured to colourless, but can be painted over other colours to make different colours. Thermochromic paints can be used in cups etc, to show when they are too hot. Phosphorescent Paints: Phosphorescent paints are glow in the dark paints, that absorb the energy from daylight, and then slowly release this energy as light. We used to use radioactive paints in watch dials, until the manufacturers started to develop cancer! C2 B – Construction Materials Raw Materials Most modern buildings are made of materials dug out of the earth. Limestone, marble and granite are used in buildings. Limestone is a sedimentary rock. This type of rock is made by fragments settling into layers. Marble is a metamorphic rock. This means the rock has been changed. In the case of marble, it is a form of limestone which has been subjected to heat and pressure making it harder than original limestone. Granite is an igneous rock. Igneous rock is formed out of liquid rock that cools slowly and forms interlocking crystal as it solidifies. The Cement and Concrete Cement is made from limestone which is a form of calcium carbonate. When the calcium carbonate is heated it thermally decomposes to form calcium oxide and carbon dioxide. Cement, sand and gravel mixed with water and left to set is called concrete. Quarries can cause dust pollution, damaged landscape and take up a lot of space. If the quarries were not there then the land could be used as a rubbish tip, covered with soil and planted with trees or left to fill with water and used for sailing and fishing. More on Thermal Decomposition Thermal decomposition is the chemical breakdown of a compound into at least two other compounds under the effect of heat. Calcium carbonate thermally decomposes at a high temperature. CaCO3 CaO + CO2 Calcium carbonate calcium oxide + carbon dioxide Reinforced Concrete Concrete is very strong under compression. It is much weaker under tension. Steel is strong under tension. Steel rods are inserted into concrete reinforcing them. The steel rods stop the concrete from stretching under tension. Grade B Grade A Key points to remember about the structure of the Earth. Tectonic plates move very slowly in different ways -The outer layer is called the lithosphere -Apart -It is made of the crust and part of the mantle underneath. - The tectonic plates are less dense than the mantle and ‘float’ on it. -Two kinds of plates -Continental plates carry continents -Oceanic plates that lie underneath oceans Crust is too thick for anyone to drill through it – yet. Most knowledge comes from measuring seismic waves produced by Earthquakes. -Collide -Scrape sideways past each other Energy from the hot core is transferred to the surface by slow convection currents in the mantle. Early explanations for the movement of tectonic plates was that they were dragged by convecting mantle like a conveyer belt. Now they think that it is more complicated. Grade A Subduction The two types of tectonic plates have different densities. -Oceanic plates are more dense than continental plates and sink low down into the mantle. Oceans accumulate on top of them. -Continental plates float high up in the mantle. When two plates collide the more dense oceanic plate sinks below the less dense continental plate. This is called subduction. Subduction zones are where plates are being destroyed The oceanic plate partially re-melts and is reabsorbed into the mantle. Some of the molten rock works its way back up the surface and creates a chain of volcanoes. The subducting oceanic plate does not move smoothly; it slips at intervals. When it slips the vibrations cause earthquakes. Grade B Magma rises through the Earth’s crust because it is less dense. It then cools and solidifies into igneous rock either after it comes out of a volcano as lava, or before it even gets to the surface. Igneous rocks have different crystal structures. -Small crystals- it has cooled rapidly (close to the surface) -Large crystals – it has called slowly (further from the surface and better insulated) Example of rock type Small crystal Large crystal Iron-rich magma Basalt Gabbro Silica-rich magma Rhyolite Granite Grade A Magma and volcanoes Iron-rich magma - Or basaltic magma tends to be runny. - Fairly ‘safe’ - Lava spills over edges of volcano and people who live near it can get away. Silica-rich magma -Less runny -Erupts quietly or explosively -Dissolved gases in the magma have no time to escape from the stiff liquid -Shoots out clouds of hot ash and pumice -Rain turns ash into mudslides -Falling ash could include volcanic bombs Geologists investigate past eruptions by looking at ash layers. In each eruption, course ash falls first followed by fine ash, producing graded bedding Future eruptions can sometimes be predicted with the help of seismometers. This method is not precise and disasters still occur. Metals and Alloys • Copper is easily recyclable as it melts down easily. • • • Copper must be sorted carefully before recycling so different grades of copper aren’t mixed. Coper must first be analysed before recycling. Impure copper has to be electrolysed before it can be used in areas where pure copper is needed, like electrical wiring. In the purification of copper we use a copper sulfate electrolyte and copper electrodes: The anode is made of impure copper and the cathode of pure. The anode dissolves in the electrolyte and the cathode is plated in pure copper. The cathode is a thin sheet of pure copper, this • • • • • Most metals form alloys. Alloys have lower melting points than the pure metal. Bronze is an alloy of copper and tin. It’s harder than copper and shrinks slightly when it solidifies so it is easy to cast. Steel contains iron. Stainless steels are much stronger than pure iron and they do not rust. Nitinol is a smart alloy made from nickel and titanium. Smart alloys can change shape at different temperatures, this is called shape memory. Smart alloys have a number of uses, one of which is a showerhead that reduces the water supply if the water gets too hot that it may cause damage. Cars For Scrap Rust is a brownish solid that forms when oxygen and water, which are needed for the reaction to happen, react with iron or steel.Salt water and acid rain speed up the reaction of rusting. Rust is a chemical reaction between iron, oxygen and water. The chemical name for the product is Hydrated Iron(III) Oxide. This is a type of reaction called oxidation because the iron reacts with oxygen to make an oxide. Iron and aluminium • Pure iron and pure aluminium aren’t very strong so they are made into alloys. An alloy is a mixture of a metal and another element, for example steel is a mixture of iron and carbon. Often an alloy is a mixture of metals. • Old cars are often dumped and taken to a scrap yard where their parts get recycled. • Iron and aluminium can be separated from each other because iron is magnetic but aluminium isn’t. In the scrap yard the car body is cut into smaller pieces, then an electromagnet attracts the iron and steel parts. • Recycling makes sense because: – It reduces the amount of rubbish that goes into landfill sites – It avoids environmental damage (mining and quarrying) – Aluminium and iron are finite sources so they will eventually run out Different materials in cars are used for different reasons: Material and its use Reasons material is used Aluminium in car bodies and wheel hubs Does not corrode, less density, malleable, quite strong Iron or steel car bodies Malleable, strong Copper in electrical wires Ductile, good electrical conductor Lead in lead-acid batteries Conducts electricity Plastic in dashboards, dials, bumpers Rigid, does not corrode, cheap PVC in metal wire coverings Flexible, does not react with water, electrical insulator Glass and plastic/glass composite in windscreens Transparent, shatterproof Fibre in seats Can be woven into textiles, can be dyed, hard-wearing Iron vs Aluminium • Iron is stronger and harder which is important in a crash. • Iron is cheaper to make a car body out of. Property Aluminium Iron Corrosion in moist air No obvious corrosion Rusts rapidly Density in g/cm)2 2.7 7.9 Melting point in degrees celsius 660 1527 Boiling point in degrees celsius 2467 2750 Magnetism Not attracted to a magnet Attracted to a magnet • Aluminium-bodied cars have a better fuel economy than a similar car made from iron • Aluminium is more malleable than iron • Aluminium doesn’t corrode as easily as iron, so has a much longer lifetime. • Aluminium is less dense than iron so the mass of the car body is less than one made of iron. Clean air Clean air is made up of 78% nitrogen, 21% oxygen and 1% other (containing carbon dioxide). These do not change often because of the balance between processes that use carbon dioxide and produce oxygen and vice versa. These processes are in the carbon cycle Clean air If the composition of the air changes then it is due to the factors; increased energy usage, increased population and deforestation. This is the theory of the evolution of the atmosphere; first of all the original gases came from the centre of the earth in a process called degassing, the original gases were ammonia and carbon dioxide, then the ammonia reacted with rocks to produce nitrogen and water, the percentage of nitrogen increased and because it is unreactive very little was removed from the atmosphere, then photosynthesising organisms evolved and produced oxygen, as the amount of oxygen increased the carbon dioxide percentage decreased until the atmosphere of today's levels were reached. Clean air These are some pollutants in the atmosphere. Pollutant Where it comes from Environmental effects Carbon monoxide Incomplete combustion Poisonous gas Oxides of nitrogen Reaction of nitrogen and oxygen in internal combustion engines Photochemical smog, acid rain Sulfur dioxide Acid rain Combustion of fossil fuels with sulfur impurities Catalytic converters are used to reduce the amount of the pollutants. Catalytic converter Carbon monoxide hydrocarbons oxides of nitrogen Not fitted 5.59 1.67 1.04 Fitted 0.61 0.07 0.04 Clean air Catalytic converters contain a rhodium catalyst. A reaction between nitric oxide and carbon monoxide contain takes place on the surface of the catalyst the reaction forms nitrogen and carbon dioxide. Carbon monoxide + nitric oxide = nitrogen + carbon dioxide 2CO + 2NO = N2 + 2CO2 Faster or Slower [1] Explosions: •Are caused by chemical reactions •Very fast reaction that makes lots of gas •The force of the explosion is caused by the gas molecules moving away from the centre Speed of Reaction: •Reactants are made into products during chemical reactions •Chemical reactants take place when particles collide with each other •The speed of a reaction can be controlled by the: * Concentration of the reactants * Pressure of reactants that are gases * Temperature of the reactants * Surface area of the reactants When any of these factors are increased the rate of reaction will also be increased as the particles either move faster, have less room to move in, have a bigger area to collide with or have more particles to collide with and all of these factors create more successful collisions per second. Simple collision Theory: • The more successful collisions there are per second the faster the process of the reaction. • For a successful collision to occur the particles must be moving very fast ad have a lot of kinetic energy. Diagram B represents the fastest chemical reaction process in both of these examples: A = has a lower concentration B = has a higher concentration A = has a lower temperature B = has a higher temperature (the arrows on B show that the particles are moving faster) A = has lower pressure B = has higher pressure A = has a smaller surface area B = has a larger surface area (a magnifying glass showing that the particles have a larger surface area) Note: It isn’t the number of collision that determines the rate of reaction it is the collision frequency. The more successful collisions per second the faster the reaction. Measuring the rate of Reaction: Most chemical reactions are hard to measure. Magnesium and dilute hydrochloric acid are easier to measure than others. • • • • During the reaction the magnesium fizzes in the dilute hydrochloric acid and bubbles are given off. The hydrogen released in the bubbles is then recorded in a gas syringe every few seconds. Magnesium + Hydrochloric acid > Magnesium chloride + Hydrogen The reaction time is the time taken for the magnesium to begin to react and the amount of bubbles released. When the reaction is over no more gas is made and one of the reactants is used up. C2G. Faster or Slower 2! Some factories use combustible powders such as: o Sulfur o Flour o Custard Flour o Wood Dust o Trinitrotoluene (TNT) They must be extremely careful because if the powders reach the open atmosphere they can potentially explode. They must make certain that the chance of producing a spark is very small. Therefore reducing the risk of ignition. Mwah haha, I wonder what will happen to my special combustible power is I set it alight??........ Faster or Slower 2 A powder has a much larger surface area than a block or lump of reactant. As the surface of a solid , the rate of reaction also . When a substance is in a big lump fewer reacting particles can be in contact with the reacting particles of a different substance. Whereas, if a powder reacts with another substance more reacting particles can be in contact. As the surface are increases there are more particles colliding with each other. This means there are more successful collisions per second. Successful collisions = when two chemicals collide and produce a chemical reaction. It is the collision frequency between reactant particles that is important in determining how fast a reaction takes place. The more successful collisions there are the faster the reaction takes place. When the surface area of a solid reactant increases there will be even more collisions every second. This means that the rate of reaction has increased. Reactions can happen at different speeds. Rate of reaction can be increased by temperature, concentration, pressure of particles and a larger surface area. These all help a reaction to speed up meaning more successful collisions per second. Faster or Slower 2! A catalyst is a substance added to a chemical reaction to make the reaction go faster. A catalyst does not change how much a product is made. A catalyst will never change as it is not part of the reaction. A catalyst is extremely useful when making chemicals. When a catalyst is added to a reaction it speeds it up vastly. A catalyst increases the rate of reaction. Some other properties of a catalyst are: it is unchanged at the end of a reaction only a small mass of catalyst is needed to have an effect over a large mass if reactants One catalyst is specific to a specific chemical reaction. This is because they are certain shapes so only the reactants in a certain chemical reaction fit a specifically designed catalyst. The time taken for a reaction to finish can be longer or shorter, but not faster or slower. Catalysts get particles in the correct orientation for a reaction. This means collisions need less energy to be successful. Faster or Slower 2! Most catalysts only make a specific reaction faster. They are not made for all types of chemical reactions. Copper catalyses the reaction between zinc and dilute sulfuric acid, but it will not catalyse other reactions. Unfortunately, this means that scientists have had to research and discover hundreds of different catalysts for us to use in different reactions. Examples of these are: zeolites or aluminium oxide in the cracking of long-chained hydrocarbons. rhodium-based catalysts in a catalyst converter. the use of vanadium oxide in manufacturing sulfuric acid. FACT: CFC’s produce chlorine atoms when they slowly break down the atmosphere which are catalysing the destruction of our atmospheric ozone. A catalyst does not increase the number of collisions per second. Instead it works by making the collisions that take place more successful. It helps reacting particles collide with the correct orientation. Causing a faster reaction. It also allows collisions between particles with less kinetic energy than average to be successful.