Water

• Water


  Tasteless<|>Colourless<|>Neutral (pH 7)<|>Dissolve ionic compounds (polar solvents)
• Test for water


  1. Physical tests: Use boiling point and melting point

  2. Use universal indicator (turns green in presence of water)
• Test for water


  1. Chemical tests: Use cobalt chloride paper (turns pink in presence of water)

  2. Use anhydrous copper (ii) sulphate (turns blue in presence of water)
• Water of crystallization


  5H2O and 6H2O that can be lost when a compound is heated
• Hydrolysis


  Breaking down (digesting) a compound using water
• Hygroscopic


  A substance (e.g. salt) absorbs moisture from the environment but does not dissolve in the moisture
• Deliquescence


  A substance (e.g. salt) absorbs moisture from the environment until it dissolves in the moisture
• Efflorescence


  A salt gives out moisture to the environment, forming a powder
• Dehydration


  Removal of combined water from a compound, forming an anhydrous salt
• Hard water


  Water that does not readily form lather with soap, instead forming scum
• Scum is a white precipitate of calcium or magnesium stearate
• Soap molecule


  Sodium stearate (NaSt)
• What causes hardness of water

  Presence of calcium (Ca2+) and magnesium ions (Mg2+) in water
• Compounds causing hardness of water

  • Calcium hydrogen carbonate
  • Magnesium hydrogen carbonate
  • Calcium sulphate
  • Magnesium sulphate
• Temporary hardness


  Caused by hydrogen carbonates of magnesium and calcium, can be removed by boiling
• Permanent hardness


  Caused by sulphates of calcium and magnesium, cannot be removed by boiling
• Measuring hardness of water

  Add soap, shake, count number of spatulas or drops required to form lather
• The fewer the number of spatulas or drops of soap required to form lather, the softer the sample of water
• Softening hard water


  1. Physical methods: Boiling/Heating, Distillation

  2. Chemical processes: Addition of washing soda, Ion exchange columns
• Advantages of hard water

  • Gives pleasant taste
  • Has calcium ions good for bones
  • Coats pipes and prevents rusting
• Disadvantages of hard water

  • Coats hot water pipes and makes them less efficient
  • Wastes soap
• Pollution


  Introduction of contaminants into the environment
• Water pollution


  Contamination of water with soluble and insoluble substances called pollutants
• Major water pollutants


  • Sewage
  • Industrial wastes
  • Agricultural wastes
• Sewage


  Wastes from toilets, high in organic matter that can be decomposed by microorganisms, leading to high biological oxygen demand (BOD)
• Biological oxygen demand (BOD)


  Amount of oxygen needed in a specific volume of water to decompose organic matter
• Industrial wastes


  • Toxic chemicals (e.g. mercury, cyanides, lead)
  • Oil (floats on water and reduces oxygen dissolution)
  • Detergents (biodegradable, use up dissolved oxygen)
• Agricultural wastes


  • Fertilizers (can cause eutrophication)
  • Pesticides and insecticides (toxic to water animals)
• Detergent


  Cleaning chemical made up of a hydrophilic head (dissolves in water) and a hydrophobic tail (dissolves in oil)
• Cleansing action of soap

  Hydrophobic tails dissolve in grease, hydrophilic heads remain in water, causing grease to break up into small droplets suspended in water