8 - Chemical analysis

• A formation is a mixture designed as a useful product.
• Pure - Single element/compound
• Purity - Measure of how pure something is
• An impure sample should have a higher boiling point, over a range.
• Chromatography - A method used to separate the dyes in an ink.
• Chromatography paper - Stationary phase, substances/molecules cannot move
• Solvent front - A pencil line where solvent reached. Measure distance from baseline.
• Beaker - Can add a lid to prevent evaporation of any liquid.
• Baseline - Drawn in pencil as it is insoluble.
• Solvent - Liquid that can dissolve substances. Mobile phase - Substances/molecules can move in it.
• Separated dyes - Spot has travelled further (more soluble). Spot has not moved (insoluble in that solvent).
• Inks to separate - Mixture of dyes, in one spot = pure. Any spots at the same height = same substance.
• Dyes travelled further = more attracted to the mobile phase.
• Dyes travelled less = More attracted to stationary phase.
• Rf = distance of spot / distance of solvent front

  Usually in mm. Rf value is a number from 0 to 1 to show how far a spot has travelled compared to others.
• CHROMOTOGRAPHY PRACTICAL RQ

  • Draw a pencil line horizontally at the bottom of the chromatography paper.
  • Using a capillary tube place a small dot of each dye along the baseline
  • Add solvent to the beaker and insert chromatography paper, making sure the solvent is partly submerging the bottom of the paper
  • Wait for the solvent to travel up the paper and draw another pencil line marking the solvent front
  • Dry the chromatography paper
  • Calculate Rf value using the equation (insert equation)
• H2 test

  • Add lit splint
  • Squeaky pop noise/H2 ignites
• O2

  • Add a glowing splint
  • It relight
• CO2

  • Bubble through limewater
  • Should go cloudy
• Cl2

  • Add damp litmus paper
  • Bleached white
• 2 methods for testing for cations

  • Flame
  • NaOH
• FLAME TEST

  • Doesn't work for mixtures of metals as colours mask each other.
  • Use a nichrome wire (cleaned w/acid) or a damp splint, the compound is added to a blue flame and the colour change is observed.
• FLAME TEST

  Lithium - Red/Crimson
• FLAME TEST

  Sodium - Yellow-orange
• FLAME TEST

  Potassium - Lilac
• FLAME TEST

  Copper - Green
• FLAME TEST

  Calcium - Red-orange
• FLAME TEST

  Strontium - Red
• NaOH TEST

  • Forms coloured precipitates (ppt)
  • ppt = a solid in a solution
  • Can test further using flame test
• NaOH test

  Cu2+ = blue ppt
• NaOH test

  Fe3+ = brown ppt
• NaOH test

  Fe2+ = green ppt
• NaOH test

  Mg2+, Zn2+, Al3+, Ca2+ = white ppt

  However if further NaOH is added to Al3+, the ppt redissolves
• 3 types of anions

  • Carbonate (CO3)
  • Sulfate (SO4)
  • Halide (Gr.7)
• LOOK IN BOOKLET FOR EQUATIONS!!
• CARBONATE

  • Add acid to the carbonate compound to produce CO2
  • Pass it through limewater, if it turns cloudy = CO2 is present
• SULFATE

  • Add HCl to a sulfate, followed by BaCl2 (Barium Chloride)
  • A white ppt is formed
• HALIDES

  • Add HNO3 (Nitric acid) to a halide compound, followed by AgNO3 (silver nitrate) then coloured precipitates are formed
  • Cl compound = white ppt
  • Br compound = cream ppt
  • I compound = yellow ppt
• Instrumental analysis - Using machines (spectrometers) to analyse compounds to find out information/composition.
• An example of instrumental analysis is Flame emission spectroscopy which is an alternate method to find metal ions in a solution.