sec 1 science chapter 4

• Purpose of separation techniques

  • Reduce, reuse, recycle for sustainable living
  • Make products
  • Provide services to allow for a good quality of life and sustainable living
• Constituents of mixtures retain their physical properties.

  Factors to consider:

  • Cost
  • Reliability
  • Environmental impact
• Magnetic attraction

  • Used to separate magnetic substances from non magnetic substances
  • Magnetic materials are attracted by the magnet while non magnetic materials are left behind
  • quicker and more efficient separation of magnetic materials from non magnetic materials
  • Examples: Iron obtained from scrap metal in a junkyard can be reused or recycled, reducing waste
• Filtration

  • The process of separating substances of different particle sizes using a sieve
  • technique used to separate an insoluble solid from the liquid in a solid liquid mixture.
  • A sieve has small holes known as pores, which is of a particular size
  • Particles smaller than pores can pass through
  • Particles bigger than pores are retained
  • Mixture is poured onto the filter funnel lined with filter paper
  • Pores allow water particles to pass through, but retains the chalk particles which are bigger
  • Liquid passed through= filtrate
  • Solid left behind= residue
• Applications of filtration

  • Tea strainer
  • -separates tea leaves from tea
  • Siltation pond
  • -Sand and rocks of different sizes are laid as filters so groundwater is filtered while flowing through holes between them
  • Nose
  • -Nostril and mucus hair, the thick liquid in the nose, helps to trap large solid particles from inhaled air to prevent them from entering the lungs
  • Produce drinking water
• Evaporation

  • The process used to obtain dissolved solute from a liquid
  • Solvent changes from liquid to gas as it is at a lower temperature than the solute, leaving behind the solute as the residue
  • Heat is applied to the salt solution, it speeds up the change of water to water vapour as the water changes state at a lower temperature than salt, so salt if left behind as residue
• Applications of evaporation

  • Decomposition
  • Preserve food
  • -Production of herbs, spices, dried small fishes
  • Production of salt
  • -In a salt mine, hot water is pumped deep into the ground to dissolve the salt, afterwards, the salt solution is pumped onto the ground and the water evaporates, leaving the solid salt behind as residue in the pans
• Distillation

  • The process that separates substances with different boiling points through boiling and condensation
  • When the mixture boils, the vapour with the lowest boiling point enters the condenser first, where it condenses when it comes into contact with a lower temperature surface. Liquid is collected and other substances are left behind as residue.
  • Salt solution is heated till boiled and the steam passes through the condenser with cold water running continuously. It cools and condenses (distillates) and salt is left behind a residue
• Solar distillation

  • Similar to water cycle processes
  • We collect water when its supply is irregular
  • Water evaporates from the ground and vapour condenses on a cool plastic sheet, to obtain pure water
• Applications of distillation

  • Making perfumes
  • -Petals boil in water and the vapour (distillate) is made into perfume
  • Produce distilled water
  • -Water contains minerals and impurities which is removed through distillation
  • Make food flavourings
  • -Citrus oil, liquid extracts such as herbs and spices are inlcuded
  • Obtain drinking water from seawater
• Paper chromatography

  • To separate small amounts of substances that dissolve to different extents in a particular solvent
  • More soluble in solvent, will travel longer distance from the start point
  • Insoluble in solvent, will remain at start point
  • A drop if ink/dye is placed near the bottom of a filter paper and is dipped in water which travel up the paper with the substances
• Applications of paper chromatography:

  • Identify colours in a dye
  • Identify coloured substances in food products
  • Detect water pollutants to ensure cleanliness of water
• Uses of water

  • Essential to stay alive
  • Regulate temperature
  • Maintain body functions
  • Fabricate, process, wash, dilute, cool and transport products
  • Cook, wash and clean
  • Swim, canoeing
  • Singapore does not have enough space to collect or store water
• Sources of water, four national taps

  1. Rainwater from local catchment

  • Network of drains/canals/rivers
  • Channeled to reservoirs for storage
• 2. Imported water

  • Supplements water supply from local catchment
• • Transported by pipelines to waterworks
  • Chemically treated, filtered and disinfected
  • Removes harmful bacteria to become clean, odorless, safe to drink
  • Within WHO guidelines
• 3. NEWater

  • Ultra clean, high grade recycled water
  • Used water from sewers are sent to water reclamation plants for treatment, then sent to NEWater for further purification
  • 1.Microfiltration
  • Microscopic particles and bacteria are removed
  • 2.Reverse Osmosis
  • Undesirable contaminants and viruses are removed
  • 3.Ultraviolet disinfection
  • Passed through UV light
  • Destroys remaining bacteria and viruses
  • Adds chemicals
  • Meets water quality requirements
• 4. Desalinated water

  • Distillation or reverse osmosis
  • Using distillation uses up too much energy and is unsustainable as a large amount of fuel is needed to heat up the water
  • Using reverse osmosis, pre treated seawater is pumped through partially permeable membranes in high pressure
  • The membranes are thin pieces of materials which have small pores so only water particles can pass through
  • Does not allow microorganisms like bacteria or chemical contaminants to pass through
  • Pure water is obtained
• Conservation of water

  • Reduce wastage and reuse water
  • Reduce, reuse and recycle
  • Protect water resources:
  • Do not throw litter/ release animals into waterways/ reservoirs
  • Leads to sustainable living
• Table salt is made up of sodium and chloride.
• Differences between evaporation and distillation

  Water evaporates into the air during evaporation, but water evaporates and condenses back again during distillation.