GCSE: OCR gateway: C2: Fertilisers and crop yields + chemicals from the sea

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  • C2
    • Fertilisers and Crop Yields
      • Growing Crops
        • Fertilisers must be dissolved in water before they can be absorbed through plant roots as the dissolved substances are small enogh to be absorbed
        • Fertilisers increase crop yield
          • Replacing essential elements used by the pervious crop
            • Providing extra essential elements
          • Providing nitrogen that makes plant protein + increases plant growth
      • Eutrophication
        • Fertilisers are washed off fields
          • Fertilisers increase nitrate and phosphate levels in ponds, rivers, and lakes
            • Algae grow rapidly
              • Algae block sunlight to oxygen producing plants which die
                • Aerobic bacteria use up oxygen in water and feed off dead/decaying plants
                  • Most living organisms  die
        • Exccessive use of fertilisers may contaminate water supplies
      • Preparing Fertilisers
        • Many fertilisers are salts
          • So they can be made: ACID + ALKALI = SALT + WATER
        • Making fertilisers
          • Alkali is titrated with acid using indicator to find quantities
            • Acid and alkali have reacted completely to produce a neutral of fertiliser contaminated with indicator solution
              • Titration results to repeat experiment using correct quantities
                • Dissolved fertiliser heated to evaporate most water off
                  • Left for remaining solution to crystallise
                    • Crystals then fitlered off
    • Cemicals from the sea; chemistry of sodium chloride
      • Mining and subsidence
        • Salt mined in Cheshire
          • From ground as rock salt
          • Solution mining: water pumped up and saturated salt solution extracted
      • Electrolysis of sodium chloride solution
        • Hydrogen made at cathode
        • Chlorine made at anode
        • Hydrogen and chlorine are reactive
          • So have to use inert electrodes so products don't react before they are collected and electrodes do not dissolve
        • Na+ ions and H+ ions migrate to cathode
          • Electrons gained so reduction
            • 2H+ + 2e- = H2
        • Cl- and OH- ions go to anode
          • Electrons lost so oxidation
            • Na+ + OH- = NaOH
      • Uses
        • Holdhold bleach
        • Solvents
        • Plastics
        • Paints
        • Soaps
        • Medicines
        • Food additives


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