Separation techniques

• The world around us is filled with naturally occurring mixtures, and we often want to separate these mixtures into their components to collect useful or precious chemicals
• Mixture


  Two or more substances that have been physically and not chemically combined
• Mixtures may contain combinations of gases, liquids, and solids that can be separated through physical means
• Physical change


  A change in the physical properties of a substance that does not involve a change in its chemical composition
• Physical changes


  • Changing between the physical states of solid, liquid, and gas
  • Dissolving into or precipitating out of solution
  • Physically separating the components of mixtures
• We need to consider the physical properties of a mixture when selecting separation techniques
• Physical properties


  • Particle size
  • Density
  • Melting and boiling points
  • Solubility
  • Magnetism
  • Electrostatic attraction
• In a mixture, pure substances retain their distinct physical properties, and any differences in these physical properties can be used to separate mixtures
• Sieving


  Particles smaller than the holes in the sieve pass through, while substances with larger particles collect in the sieve
• Blackbeard the pirate used a sieve to separate a heterogeneous mixture of gold coins and sand
• Heterogeneous mixture


  A mixture that has variable composition and properties
• Homogeneous mixture


  A mixture that has uniform composition and properties
• Density


  The mass of a substance per unit volume
• Water has a density of approximately 1 gram per cubic centimeter, while iron has a density of 7.8 grams per cubic centimeter</b>
• Mass or weight of a substance is not the same as its density
• Sedimentation


  Insoluble particles suspended in mixtures are allowed to settle out from liquids or gases, often when the liquid or gas is stationary
• Decantation


  Pouring off a liquid from above insoluble particles that have settled at the bottom of a mixture
• Miscibility


  The ability of a liquid solute to dissolve in a liquid solvent
• Immiscibility


  When two liquids cannot dissolve in each other, regardless of the proportions in which they are mixed
• Centrifugation


  Rapidly spinning a mixture of substances that have different densities, causing the more dense solids to fall to the bottom and the less dense liquid to float on top
• Separation funnel


  A piece of laboratory glassware used to separate two immiscible liquids of different densities
• Milk is a heterogeneous mixture containing fat, water, and other substances
• Water and lamp oil are immiscible, so they can be separated using a separation funnel
• Separation techniques


  • Sieving
  • Sedimentation
  • Decantation
  • Centrifugation
  • Separation funnel
• The physical properties of a substance include particle size, density, melting and boiling points, solubility, magnetism, and electrostatic attraction