T2W3L2

• pure substances have a fixed or constant composition
• cannot be separated by physics means
• well defined physics properties, e.g:
  • melting point
  • boiling point
  • hardness
  • density
  • colour
• have constant chemical properties

mixtures §

• contains two or more diff substances, in proportions that can vary
• properties vary with composition, depend on the identity and amounts of constituents
• properties of individual constituents can be used to separate the mixture

separating mixtures §

• sieving
• filtration (diagram)
  • use to separate heterogeneous mixtures composed of solids and liquids
  • uses a porous barrier to separate the solid from the liquid.
  • smaller particles of liquid passes through leaving the solid in the filter paper
• decanting
  • done to separate particulates from a liquid by allowing the solids to settle to the bottom of the mixture and pouring off the particle-free part of the liquid.
  • another method is to allow two immiscible liquids to separate and the lighter liquid is poured off.
  • separating funnel is better than decanting
• use of separation funnel (diagram)
  • dehydrating agent to remove water
  • something filtered using funnel is called filtrate
• distillation (diagram)
  • you need to be very careful and selective
  • a question might ask for you to choose a method
    • if this is the case, identify if substances is homogenous or heterogenous
  • distillation works for homogenous, LIQUID homogenous mixtures
  • if it is simple distillation, there must be a NOTICEABLE difference in boiling point.
  • eg water and ethanol works for distillation
  • you can use heating mantle instead of bunsen burner
  • 
  • you should be able to label this (no need to draw diagram)
  • not incl: water outlet label, distillate label
• fractional distillation (basic diagram)
  • when the boiling point is too close together for normal distillation.
    • more than 2 things to be separated
• electrostatic attraction
• magnetic susceptibility
• vaporisation
• crystallisation
• chromatography
• centrifuging
• evaporating
• dissolving
• sieving
  • a porous material is used to separate particles of different sizes.
  • method is most commonly used to effect gross separations, as of liquids from suspended crystals or other solids.
  • to accelerate filtration, pressure usually is applie.
  • a series of sieves is stacked, with the screen of largest hole size at the top.
• flotation

homogenous materials §

• have uniform compositions throughout
• include all pure substances (elements and compounds) and some mixtures.
• the only kind of mixture that is homogenous is a solution, eg: salt water.

heterogeneous materials §

• materials are non-uniform - you can see differences from one section to another
• the constituents are physically separated, eg: in a different phase
• examples include
  • granite (mixture of mineral grains)
  • milk (fat globules suspended in water)
  • toothpaste (solid particles suspended in liquid)