Chemistry p1

• Element


  All of the atoms are the same
• Compound


  Contains two or more different elements chemically combined in fixed proportions
• Compounds usually have totally different properties to the elements that they're made from</b>
• Mixture


  Contains different elements or compounds, but they are not chemically combined
• Separation techniques for mixtures

  • Filtration
  • Distillation
  • Crystallization
  • Chromatography
• Molecule


  Any elements chemically combined, even if they are the same element
• Molecules


  • Methane
  • Water
  • Ammonia
  • Chlorine
  • Oxygen
• Molecules that are not compounds contain the same element chemically combined
• Chemical formula


  Tells us the elements in a molecule and the numbers of atoms of each element
• In a specific compound, the number of atoms of each element is fixed and cannot be changed</b>
• Physical separation techniques can only be used to separate mixtures, they cannot be used to separate the elements in a compound
• Chemical reactions such as reduction or electrolysis can be used to separate the elements in compounds
• Filtration


  Used to separate an insoluble solid from a liquid
• Insoluble


  The solid will not dissolve in the liquid
• Example of insoluble solid and liquid


  • Silver chloride and water
• Filtration process


  1. Pour mixture into filter paper

  2. Liquid (filtrate) passes through

  3. Solid trapped in filter paper
• Crystallization


  Used to separate a soluble solid from a liquid
• Example of soluble solid and liquid


  • Sodium chloride and water
• Crystallization process


  1. Leave solution to evaporate

  2. Water evaporates

  3. Solid crystals left behind
• Heating can be used to speed up crystallization, but some chemicals may break down if heated
• Simple distillation


  1. Evaporate the liquid by heating

  2. Condense the vapor back to a liquid by cooling
• Simple distillation apparatus


  • Flask with solution
  • Continuous glass tube
  • Condenser with cold water circulation
  • Thermometer
• Heating the solution


  Liquid starts to evaporate, turning into a vapor
• Vapor passing over the thermometer

  Thermometer reading increases
• Vapor passing through the cold condenser

  Vapor condenses, turning back to a liquid
• Uses of simple distillation


  • Producing drinking water from sea water
• Simple distillation requires a great deal of energy, so it is generally not used to produce drinking water
• Fractional distillation


  A process used to separate a mixture of different liquids based on their different boiling points
• Fractional distillation


  • Requires a mixture of liquids with different boiling points
  • Uses a fractionating column containing glass beads to increase the separation of the liquids
• Fractional distillation


  1. Heat the mixture

  2. Vapors enter the fractionating column

  3. Vapors condense and drip back into the flask

  4. Repeated evaporation and condensation increases the concentration of the lower boiling point liquid

  5. Thermometer measures the temperature as the vapors pass through

  6. Collect the fractions as the temperature reaches the boiling points of the different liquids
• If the two liquids have very similar boiling points, it is much harder to separate them and multiple rounds of fractional distillation may be required
• The equipment shown is not suitable for separating very large volumes of liquid, such as when refining crude oil
• Paper chromatography


  A separation technique used by scientists to separate substances in a mixture
• Paper chromatography is a physical process that does not involve chemical reactions and no new substances are made
• Stationary phase


  The paper, which does not move
• Mobile phase


  The solvent, which moves up the paper
• Paper chromatography procedure


  1. Draw pencil line at bottom of paper

  2. Put dots of substances on line

  3. Place paper in solvent

  4. Solvent moves up paper, dissolving and carrying substances

  5. Substances separate based on solubility
• A pure compound will produce a single spot in all solvents, while compounds in a mixture may separate into different spots
• More soluble substance


  Travels further up the paper than less soluble substance
• The pencil line is used so that the pen ink does not dissolve and move up the paper