C3: Topic 3

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  • C3: Topic 3
    • Electrolysis
      • Electrolysis is when an ionic substance is broken down using electricity which form useful elements or compounds.
      • It needs a direct current. the electrodes are made from graphite or unreactive metals such as copper. During electrolysis the positive ions (cations) are attracted to the negative electrode. They gain electrons there and so are reduced. negative ions (anions) are attracted to the positive electrode. they lose electrons there and so are oxidised.
    • Making and using sodium
      • Uses of Sodium: The yellow light is given out when an electric current is passed through sodium vapour in the lamp: sodium is used in street lamps. liquid sodium has a high 'heat capacity' this makes it useful as a coolant in some nuclear power stations.
    • Electrolysis of salt water
      • Electrolysis of the aqueous sodium chloride provides three useful products; hydrogen, chlorine and sodium hydroxide solution.
        • REMEMBER! Reduction happens at the cathode and oxidation happens at the anode!
    • More electrolysis
      • To purify copper using electrolysis the copper ions move to the copper electrode, gain electrons and are discharged as pure copper. The electrodes are in copper sulphate solution. the ions are replaced by copper ions from the impure copper anode. at the bottom of the anode sludge is formed- this contains metals such as silver.
      • Molten lead bromide produces lead and bromine. When the electrolyte is a solution, hydrogen ions and hydroxide ions from the water may be discharged. For example, copper sulphate solution produces copper at the cathode and oxygen at the anode. But sodium sulphate solution produces hydrogen at the cathode and oxygen at the anode.
    • Fertalisers
      • Nitrogenous Fertilisers: they replace the soil minerals used by plants as they grow. they help plants grow therefore increasing crop yields. Nitrogenous fertilisers contain nitrogen compounds.
      • Making Fertilisers: Nitrogenous fertilisers are made from ammonia. Ammonia is made from nitrogen and hydrogen in the Haber process. Nitrogen is extracted from the air. Hydrogen is made from natural gas this is mostly methane.
      • If a farmer uses too much fertiliser in a field, it can have a big effect on the local wildlife. The excess fertiliser will run into a river during the rain and will make the algae grow faster so the surface of the river will be covered. No light or oxygen will be getting into the water therefore the plants will die. furthermore because the plants die the fish wont be able to eat anything so they also die.
      • Reversible Reactions: Forward reaction- N2 + 3N2 ---> 2NH3 Backward reaction- 2NH3 ---> N2 + 3H2
    • Equilibrium
      • Dynamic Equilibrium: A reversible reaction  may reachequilibrium if it happens in a close area. in the haber process nitrogen and hydrogen react to make ammonia: nitrogen + hydrogen ammonia. At equilibrium, the rate of the forward and backwards reaction happen at the same rate. the concentration of the substances also stay the same. Its called a dynamic equilibrium because the two reactions are still happening.
      • Position of Equilibrium: The concentrations of all substances at equilibrium don't have to be the same. If the concentrations of the substances  on the right of the equation are greater than the concentrations of the substances on the left, we say that the position of equilibrium is to the right. If a reversible reaction involves gases and the pressure is increased, the position of equilibrium moves in the direction of the fewest molecules of gas. If the temp is increased the position of the equilibrium moves in the direction of the endothermic change.
      • If the forward reaction is endothermic, the backwards reaction will be exothermic.
    • The Haber process
      • Catalysts: A catalyst is a substance that speeds up the rate of a reaction without being used up. It makes the forward and backward reaction increase by the same amount therefore, it does not change the position of the equilibrium but does reduce the time needed to reach the equilibrium. Catalysts are important as they reduce the cost in industrial processes.
      • The Haber Process is and industrial process for manufacturing ammonia. The conditions needed for the Haber process are usually: an iron catalyst, a high pressure and a temperature of about 450 degrees.
      • The forward reaction is exothermic. you would expect to use a low temp because the position of equilibrium would move to the right. but if the temp was too low, the rate of reaction would also be too slow. 450 degrees is low enough to get an acceptable yield of ammonia but high enough to get it in an acceptable time.
  • Molten lead bromide produces lead and bromine. When the electrolyte is a solution, hydrogen ions and hydroxide ions from the water may be discharged. For example, copper sulphate solution produces copper at the cathode and oxygen at the anode. But sodium sulphate solution produces hydrogen at the cathode and oxygen at the anode.

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