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• Pure substance


  Consists only of one element or one compound
• Mixture

  Two or more different substances that are not joined together
• Types of chemical substance

  • Element (contains just one type of atom)
  • Compound (contains two or more types of atoms joined together)
  • Mixture (contains two or more different substances not joined together)
• Pure substances


  • Have a sharp melting point
• Mixtures

  • Melt over a range of temperatures
• Cooling a pure substance

  Temperature stays the same while it changes state
• Cooling an impure substance (mixture)

  Temperature changes slightly as it changes state
• The different substances in a mixture can be elements or compounds
• The components of a mixture can be separated without chemical reactions
• There are different ways to separate mixtures, for example by filtration, crystallisation, distillation or chromatography
• The method chosen depends upon the type of mixture
• Distillation

  A separation method used to separate a solvent from a solution
• Solvent


  The liquid in which the solute dissolves to form a solution
• Solution

  Mixture formed by a solute and a solvent
• Dissolved

  A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution
• Solute


  The dissolved substance in a solution
• Boiling point

  The temperature at which a substance rapidly changes from a liquid to a gas
• Vapour


  Gas formed below the boiling point of a substance
• Condensed


  Turned from a gas or vapour into a liquid, usually as a result of cooling
• Concentration

  The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present
• Ethanol

  The alcohol which is produced as a result of fermentation of sugars by yeast
• Fraction

  In fractional distillation, such as that of crude oil, the different parts of the original mixture are called fractions. The substances in each fraction have similar boiling points to each other
• Crude oil


  Mixture of hydrocarbons, mainly alkanes, formed over millions of years from the remains of ancient dead marine organisms
• Methods to separate mixtures

  • Filtration
  • Crystallisation
  • Distillation
  • Chromatography
• Mixture

  Combination of two or more substances that are not chemically bonded
• The method chosen to separate a mixture depends upon the type of mixture
• Treating fresh water to make it potable

  1. Remove large objects using screens

  2. Remove insoluble particles using a coarse filter bed

  3. Clump smaller insoluble particles using aluminium sulfate, then settle in a sedimentation tank

  4. Remove very small insoluble particles using a fine filter bed

  5. Add chlorine gas to kill harmful microorganisms
• Potable water

  Water that is safe to drink
• Insoluble

  Unable to dissolve in a particular solvent
• Particle

  Small piece of matter
• Microorganism

  Microscopic living thing such as archaea, bacteria and some species of eukaryotes
• Treating seawater to produce drinking water

  1. Boil seawater

  2. Water vapour is led away and cooled

  3. Water vapour condenses to form pure water, leaving the salt behind
• Distillation


  Separation method used to separate a solvent from a solution
• Vapour

  Gas formed below the boiling point of a substance
• Condensed

  Turned from a gas or vapour into a liquid, usually as a result of cooling
• Ion

  Electrically charged particle, formed when an atom or molecule gains or loses electrons
• Water produced by distillation is useful in the laboratory for dissolving substances as it does not contain any dissolved ions that might interfere with a chemical analysis