Chemistry

A selection of the topics that are needed to revise for the Chemisrty gcse higher tier exam. 

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Atoms

  • All substances are made up of atoms, A substance that is made up of only one type of atom is called an element. There are about 100 different elements and are shown in the perodic table. The groups contain ones with similar properties.
  • Atoms are represented by chemical symbols eg Na is sodium
  • Atoms have a small central nucleus which is made up of both protons and neutrons and surronded by electrons 
  • In an atom the number of electrons is equal to the number of protons. 
  • The number of protons in an atom= the atomic number 
  • the sum of both protons and neutrons= the mass number 
  • Group 0 are noble gases. 
  • A compound which has both metals and non metals consists of Ions. The metal atoms lose electrons to form positive Ions and the non metals gain electrons to form negative ions. The opposite charges of the ions mean that they're strongly attached to each other, IONIC BONDING!
  • A compound formed from from non metals consists of molecules. Each atom shares an electron with another atom this is COVALENT BONDING! Sharing bonds! 
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Electrons and Periodic Table!

  • Each electron in an atom is at a particular energy level. 
  • The electrons in an atom occupy the lowest available energy levels. 
  • Electrons in the same group in the table have the same number of electrons on their outer shell, this then gives them similar properties.
  • Protons have +1 charge
  • Neutrons have 0 charge
  • Electrons have -1 charge
  • Goes in the structure of 2,8,8
  • Full electron shells are happy eg noble gases always have their outer shells full! 
  • Group 0 are noble gases and are stable and unreactive as there outer shell are full
  • Similar properties form columns 
  • vertical columns are groups and have the same number of electrons in their outer shell 
  • Group 1 metals Li,Na,K,Rb,Cs,Fr are all metals and react the same way. 
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Balancing Equations!

  • Atoms are never made or lost in chemical reactions!
  • Because they are never gained or lost it means the mass of the reactants equals the mass of the products. 
  • So if you react 6g of magnesium with 4g of oxygen makes 10g of magnesium oxide
  • You balance the equation by putting numbers in front of the formulaes when needed.
  • REMEMBER  
    • just balance one atom at a time
    • FInd an element that doesnt balance and try to sort it 
    • it could however make another wrong atom 
    • just try and keep on going sorting it out. 
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Limestone!

  • Limestone, mainly composed of the compound calcium carbonate is quarried and can be used as building materials, 
  • Calcium carbonate can be decomposed by heating (thermal decomposistion) to make calcium oxide and carbon dioxide. 
  • The carbonates of magnesium, copper, zinc, calcium, and sodium decompose on heating in a similar heating 
  • Calcium oxide reacts with water to produce calcium hydroxide with is an alkali that can be used in the neutralisation of acids.
  • A solution of calium hydroxide (lime water) reacts with co2 to produce calcium carbonate. Limewater is used as a test for co2. Co2 turns limewater cloudy. 
  • Carbonates react with acids to produce co2, a salt and water. Limestone is damaged by acid rain, 
  • Limestone is heated with clay to mkae cement, cement is then mixed with sand to make mortar and with sand and aggregegate to make concrete
  • Limestone produces things you want like houses and roads. Chemicals in dyes paints and medecines also come from limestone. 
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Extracting Metals!

  • Ores contain enough metal to make it econmic to extract it. 
  • Ores are mined and may be concentrated before the metal is extracted and purified. 
  • Unreactive metals such as gold are found in the earth as the metal itself, but most metals require chemial reactions to extract it.
  • Metals less reactive than carbon can be extracted from their oxides by reduction with carbon eg Iron oxide is reduced in the blast furnace to make iron
  • Metals more reactive than carbon as extracted by electrolysis, very expensive
  • Copper can be extracted from copper rich ores by heating the ores in a furnace(smelting). The copper is then purified by electrolysis. 
  • Copper can be extracted by phytomining or by bioleaching,. 
  • Copper can be obtained from soloutions of copper salts by electrolysis or by displacement using scrap iron. 
  • We should recycle the metals because extracting them uses limited resources and is expensive in terms of energy and effects the enviroment. 
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Extracting Metals! Electrolysis

  • Aliminium and titanium cannot be extracted from their oxides by reduction with carbon. Current methods of extraction are expensive because there are many stages in the process and large amounts of enery are needed. 
  • Electrolysis means splitting up with electricity
    • uses electricity
    • requires a liquid called the electrolyte
    • ogten metal salt solutions make from the ore
    • electrolyte have free ions these conduct the electricity 
    • Electrons are taken away by the (positvie) anode and given away by the (negative) cathode. 
    • As ions gain or lose electrons they become atoms or molecules and are released. 
  • Displacement reaction uses a solution
    • more reactive metals react more vigorously than less reactive metals
    • If you put a reactive metal into a solution of a dissolved metal compound, the reactive metal will replace the less reactive in the compound. 
    • because the more reactive metal bonds more strongly. 
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Extracting Metals, Displacement!

  • Displacement reaction uses a solution
    • more reactive metals react more vigorously than less reactive metals
    • If you put a reactive metal into a solution of a dissolved metal compound, the reactive metal will replace the less reactive in the compound. 
    • because the more reactive metal bonds more strongly to the non metal bit of the compound and pushes out the less reactive one. 
    • eg scrap iron can be used to displace copper from solution, this is useful because iron is cheap but copper is expensive. 
    • If some iron is put in a solution of copper sulfate, the more reactive iron will then kick out the less reactive copper from the solution. 
    • You end up with iron sulfate solution and copper metal. 
    • COPPER SULFATE+IRON----- IRON SULFATE+COPPER
    • If a piece of silver metal is put into a solution of copper sulfate, nothing happens. The more reactive metal (copper) is already in the solution.
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Bioleaching!

  • This uses bacteria to separate copper from copper sulfate. 
  • The bacteria get energy from the bond between copper and sulfur, separating out the copper from the ore in the process. The leachate (the solution produced by the process) contains copper, which can be extracted. 
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Phytomining!

  • This involves growing plants in soil that contains copper. 
  • The plants cant use or get rid of the copper so it gradually builds up in the leaves
  • The plants can be harvested, dried, and burned in a furnace. 
  • The copper can be collected from the ash left in the furnace
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Metal Extraction bad for the environment and recyc

  • Mining and extracting can use alot of energy most burns fossil fuels
  • fossil fuels are running out so its important to conserve them, contributes to acid rain, global dimming and climate change
  • Recycling metals only uses a small fraction of the energy need to mine and extract new metal. 
  • Energy doesnt come cheap so recycling saves money 
  • recycling metals cuts down on landfill sites
  • If all the aluminium cans in the UK were recycled, there'd be 14 million fewer dustbins to empty each year.
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Properties of the metals!

  • They are strong, bendy and are great conductors in heat and electricity 
  • metals in the transitions section in the periodic table have lots of everyday uses used for saucepans car bodies bridges and electrical wires. 
  • COPPER! 
    • Good conductor of electricity so ideal for wires
    • hard and strong but can be bent 
    • doesnt react with water 
  • ALUMINIUM! 
    • Corrosion resistant 
    • low density 
    • Pure aluminium isn't particularly strong but it forms hard, strong alloys
  • TITANIUM! 
    • low density metal
    • very strong 
    • corrosion resistant
  • Useful structural materials but some corrode when exposed to air and water so they need to be protected 
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Alloys

  • Iron from a blast furnace contains 96% iron. The impurities make it brittle and so it has limited uses. The other 4% is impurities such as carbon. 
  • Most iron is converted to steels, steels are alloys since they are mixtures of Iron with carbon. Some steels contain other metals 
  • Alloys can be designed to have properties for specific uses 
  • Low carbon steels are easily shaped, high carbon steels are hard and stainless steels are resistant to corrosion 
  • Most metals in everyday use are alloys. 
  • Pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use. 
  • ALLOYS ARE HARDER THAN PURE METALS! 
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Crude Oil

  • Its a mixture of a very large number of compounds 
  • A mixture consists of 2 or more elements or compounds not chemically combined together
  • the chemical properties of each substance in the mixture are uncharged 
  • It is possible to separate the substances in a mixture by physical methods including distillation, 
  • Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon atoms only (hydrocarbons)
  • Most of these are saturated hydrocarbons called alkanes with have the formula of CnH2n+2
  • CRUDE OIL IS SPLIT INTO SEPARATE GROUPS OF HYDROCARBONS
  • We can separate this by fractional distillation 
  • Crude oil is mostly alkanes.  
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ALKANES!

  • Are made up of chains of carbon atoms surrounded by hydrogen atoms
  • Different alkanes have different chain length 
  • First 4 alkanes are methane, ethane, propane and butane
  • Carbon atoms form 4 bonds and hydrogen atoms only form 1 bond 
  • the shorter the molecules the more runny the hydrocarbon is 
  • the shorter the molecules the more volatile they are this means they turn into a gas at a lower temperature, therefore the lower the temperture is which they condense and a lower boiling point 
  • shorter molecules are more flammable 
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Polymers!

  • Alkenes can be used to make polymers such as poly(ethene) and poly(propene). 
  • In these reactions monomers join together to form polymers. 
  • = double bond
  • - single bond
  • Polymers can be used for
    • packaging materials
    • waterproof coatings
    • dental polymers
    • wound dressings
    • Plastic bags 
  • Polymers are not biodegradable so they are not broken down by microbes, this can then lead to waste diposal 
  • Polymers have different physical properties
    • the physical properties are affected by the temp and pressure of polymerisation 
  • Polyethene is made at 200 celcius and is flexible with a low density 
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Ethanol and Emulsions!

  • Ethanol can be produced by the hydration of ethene with steam in the presence of a catalyst 
  • It can be produced by FERMENTATION with yeast, using renewable sources. This can be represented by 
    • sugar---carbon dioxide+ethanol 
  • EMULSIONS!
    • Oils do not dissolve in water. They can be used to produce emulsions
    • Emulsions are thicker than oil or water and have many uses that depend on their properties. 
      • They provide better texture 
      • coating ability 
      • appereance 
    • Emlusifiers have hydrophillic and hydrophobic properties 
    • Emulsifiers stop emulsions from sperating out and this gives them a longer 'shelf life' 
    • Some people are allergic to them e.g egg yolk is one 
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Vegetable and unsaturated and saturated Oils!

  • Some fruits, seeds and nuts are rich in oils that can be extracted. The plant material is crushed and the oil removed by pressing or in some cases by distillation. Water and other impurities are removed.
  • Vegetable oils are important foods and fuels as they provide a lot of energy. They also provide us with nutrients.
  • Vegetable oils have higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling. This produces quicker cooking and different flavours but increases the energy that the food releases when it is eaten. 
  • Vegetable oils that are unsaturated contain double carbon–carbon bonds. These can be detected by reacting with bromine water

Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60 °C. Hydrogen adds to the carbon–carbon double bonds. The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads and in cakes and pastries.

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The Earth!

  • The Earth consists of a core, mantle and crust, and is surrounded by the atmosphere.
  • The Earth’s crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates).
  • Convection currents within the Earth’s mantle driven by heat released by natural radioactive processes cause the plates to move at relative speeds of a few centimetres per year.
  • The movements can be sudden and disastrous. Earthquakes and / or volcanic eruptions occur at the boundaries between tectonic plates.
  • For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:
  • ■ about four-fifths (80%) nitrogen
  • ■ about one-fifth (20%) oxygen
  • ■ small proportions of various other gases, including carbon dioxide, water vapour and noble gases.
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The Earth!

  • During the first billion years of the Earth’s existence there was intense volcanic activity. This activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans
  • There are several theories about how the atmosphere was formed. 
  • One theory suggests that during this period the Earth’s atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like the atmospheres of Mars and Venus today). There may also have been water vapour and small proportions of methane and ammonia.
  • There are many theories as to how life was formed billions of years ago. 
  • One theory as to how life was formed involves the interaction between hydrocarbons, ammonia and lightning.
  • Plants and algae produced the oxygen that is now in the atmosphere.
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The Earth!

  • Most of the carbon from the carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels.
  • The oceans also act as a reservoir for carbon dioxide but increased amounts of carbon dioxide absorbed by the oceans has an impact on the marine environment.
  • Nowadays the release of carbon dioxide by burning fossil fuels increases the level of carbon dioxide in the atmosphere.
  • Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in a variety of industrial processes
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