C8

• A pure substance contains only one type of element or compound
• This means pure substances:

  Melt and solidify at one temperature called melting point

  Boil and condense at one temperature called Boling point
• Impure substances are mixtures they do not melt and boil at one temperture
• Formulations are mixtures that have been carefully designed to have specific properties
• The component in a formulation is carefully controlled quantities to ensure that the product has the required properties. They have many uses such as fuel, paints, medicine and fertilisers
• Chromatography involves:

  A stationary phase which does not more

  And a mobile phase which moves
• In paper chromatography the stationary phase is the absorbent paper and the mobile phase is the solvent often water
• Rf = distance moved by substance / distance moved by solvent
• Gas test: Hydrogen

  Properties: A colourless gas. It combines violently with oxygen when ignites

  Test for Gas: Squeaky pop test
• Gas Test: Chlorine

  Properties: A green poisonous gas that bleaches dyes

  Test for gas: Turn damp indicator paper white
• Gas Test: Oxygen

  Properties: A colourless gas that helps fuels burn more readily in air

  Test for Gas: Relight a glowing splint
• Gas test: Carbon Dioxide

  Properties: A colourless gas

  Test for Gas: When bubbles the through limewater it turn the water cloudy
• Flame emission spectroscopy is very useful instrumental method

  it is used to analyse solutions that contain metal ions

  A sample of the metal solution is placed in a flame and light emitted is passed through the spectroscope

  This produces a line spectrum which can be used:

  to identify the metal ions in a solution

  Measure the concentration of the metal ion
• Modern instrumental methods of detection and analysis give rapid results and are very sensitive can be used on small samples
• Flame tests can be used to identify metal ions (cations)
• distinctive colour indicate the presence of certain ions:

  Copper = green

  Calcium = brick red

  Lithium = Crimson red

  Potassium = lilac

  Sodium = yellow

  If a sample contains a mix of ions the colour of the ions can be masked
• Carbonates react with dilute acid to form carbon dioxide gas
• Carbon dioxide turn colourless limewater cloudy

  Most metal carbonates are insoluble

  However sodium carbonate and potassium carbonate are soluble and dissolve in water to form solutions that contain carbonate ions
• Solutions of metal compounds contain metal ions. Some of these form precipitates and insoluble material that comes out of the solution when sodium hydroxide solution is added to them. This can be seen in the chemical equation when the reactant are aq and the product is s
• Metal ion: Aluminium

  Precipitate formed: Aluminium hydroxide

  Precipitate colour: white - dissolves if more sodium hydroxide solution is added
• Metal ion: Calcium

  Precipitate formed: Calcium hydroxide

  Precipitate colour: white
• Metal ion: Magnesium

  Precipitate formed: Magnesium hydroxide

  Precipitate colour: white
• Metal ion: Copper

  Precipitate formed: Copper hydroxide

  Precipitate colour: blue
• Metal ion: Iron (Fe 2+)

  Precipitate formed: Iron (II) hydroxide

  Precipitate colour: Green
• Metal ion: Iron (Fe 3+)

  Precipitate formed: Iron (III) hydroxide

  Precipitate colour: brown
• If dilute hydrochloric acid and barium chloride solution are added to a solution contain sulphate ions a white precipitate of barium sulphate is produced
• Solutions of halide ions (Chloride , bromide and iodide ions) react with silver nitrate solution in the presence of dilute nitric acid to produce silver halide precipitates

  Sliver chloride = white

  Silver bromide = cream

  Silver iodide = yellow