Chemistry year 10

• Chemists use symbols and formulae to represent elements and compounds
• Word equations and balanced chemical equations represent the changes that happen in chemical reactions
• Atom


  The smallest part of an element that can exist
• Element


  A substance made of one type of atom only
• Chemical symbol


  • Consists of one or two letters
  • Always starts with a capital letter, with any other letter in lower case
• Chemical symbols


  • O (oxygen)
  • Na (sodium)
• There are over 100 different elements
• Elements are arranged into groups with similar properties in the periodic table
• Groups are numbered from 1 to 7, then 0 in the periodic table
• In the periodic table, metals are on the left of the stepped line, and non-metals are on the right
• There are different ways to separate mixtures, such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
• The method chosen depends on the type of mixture
• Pure (in chemistry)


  A substance consisting only of one element or one compound
• Mixture


  Two or more different substances, not chemically joined together
• The substances in a mixture can be elements, compounds, or both
• Being part of a mixture does not change the chemical properties of the substances that are in it
• Mixtures can be separated by physical processes
• Physical processes do not involve chemical reactions, and no new substances are made
• Filtration


  Method used to separate an insoluble solid from a liquid using a physical barrier such as paper
• Filtration


  • Filter paper has tiny holes or pores that are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid
• Filtration


  1. Mixture of solid and liquid is poured into the filter funnel

  2. Liquid drips through the filter paper but the solid particles are caught in the filter paper
• Crystallisation


  The process of producing crystals from a solution by evaporating the solvent
• Crystallisation


  1. Solution is placed in an evaporating basin and heated

  2. Volume of the solution decreases as some of the solvent evaporates

  3. All the solvent has evaporated, leaving solid crystals behind
• Methods to separate mixtures

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Obtaining large, regularly shaped crystals from crystallisation

  • Put the solution in an evaporating basin
  • Warm the solution by placing the evaporating basin over a boiling water bath
  • Stop heating when crystals begin to form around the edge of the basin
  • Pour the excess liquid away (or filter it)
  • Dry the crystals using a warm oven or by patting them with filter paper
• The method chosen depends on the type of mixture
• Simple distillation


  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
• Simple distillation is used to produce pure water from seawater
• Dissolved solute has a much higher boiling point


  Than the solvent
• Chromatography


  Used to separate different substances dissolved in a liquid
• Chromatography


  • Relies on two different 'phases': the stationary phase and the mobile phase
  • The stationary phase is very uniform, absorbent paper
  • The mobile phase is the solvent that moves through the paper, carrying different substances with it
• Dissolved substances


  The different dissolved substances in a mixture are attracted to the two phases in different proportions, causing them to move at different rates through the paper
• Simple distillation


  1. Solvent vapour leaves the solution

  2. Solvent vapour cools and condenses

  3. Remaining solution becomes more concentrated
• Chromatogram


  The results of separating mixtures by chromatography
• A paper chromatogram can be used to distinguish between pure and impure substances
• A pure substance produces one spot on the chromatogram, while an impure substance or mixture produces two or more spots
• Fractional distillation


  Used to separate different liquids from a mixture of liquids
• A paper chromatogram can also be used to identify substances by comparing them with known substances