C3: Topics 1 and 2

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  • C3: Topics1 and 2
    • Water Testing
      • Qualitative: investigates types of substance present
      • Quantitative: investigates the amount of each substance present
      • Flame tests: used to detect certain metal cations. Sodium: yellow Potassium: lilac Calcium: red Copper: green/blue
      • Hydroxide Precipitates: 1. Dissolve the sample in water. 2. Add a few drops of sodium hydroxide solution. They form insoluble precipitates.
    • Safe Water
      • Halide Ions: add a few drops of dilute nitric acid and a few drops of silver nitrate solution which forms a coloured precipitate. Chloride: white Bromide: cream Iodide: yellow
    • Safe Limits
      • Testing Water Purity: drinking water is not pure water as it contains dissolves substances. for example chlorine is added because it kills harmful microorganisms and aluminium sulphate is added to remove small solid particles. Its important to make sure the safe amount of these dissolved substances are added to drinking water.
        • Tests for carbonate ions: Carbonate ions can be tested for using dilute acid to a sample containing carbonate ions. the gas formed is carbon dioxide and turns limewater milky.
    • Water Solutes
      • Calculating Concentrations: concentration (g dm -3)= mass of solute (g)/ volume of solution (dm3)
      • Hard water: water in rivers flow over rocks that contain calcium and magnesium and they dissolve into the water to form hard water.
        • Problems with Hard Water: it doesn't easily form a lather when it is mixed with soap.
    • Hard and Soft Water
      • Temporary Hardness: its caused by dissolved calcium Hydrogencarbonate. It can be removed by boiling water, it works because calcium hydrogencarbonate breaks down when heated. Removing hardness from water is called softening.
      • Permanent Hardness: its caused by substances such as calcium sulphate. but it cannot be removed by boiling water.
  • Hard and Soft Water
    • Temporary Hardness: its caused by dissolved calcium Hydrogencarbonate. It can be removed by boiling water, it works because calcium hydrogencarbonate breaks down when heated. Removing hardness from water is called softening.
    • Permanent Hardness: its caused by substances such as calcium sulphate. but it cannot be removed by boiling water.

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