Chemical Tests

• Carbonate + Acid ---> Salt + Carbon Dioxide + Water
• Test for CARBONATES:

  • Add some DILUTE Hydrochloric Acid to the Carbonate
  • Take any gas that is produced and run it through Lime Water

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  If a Carbonate IS present, then the CO2 Gas produced will make the limewater bubble and turn cloudy

  
• The Sodium Hydroxide Test:

  If you react a METAL ION with a solution of Sodium Hydroxide, it will form a Coloured Precipitate (The Metal Reacts with the HYDROXIDE Ions)

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  Results:

  • IRON (II) (Fe2+) makes a [Green] Precipitate
  • COPPER (II) makes a [Blue] precipitate
  • MAGNESIUM (Mg2+) makes a [White] Precipitate
  • ALUMINIUM (Al3+) makes a [White] Precipitate, which turns colourless if there is excess NaOH
  • CALCIUM (Ca2+) makes a [White] Precipitate
  • IRON (III) (Fe3+) makes a [Brown] Precipitate

  A) White

  B) Green

  C) Brown

  D) White

  E) White

  
• The Colour of Metal Ion Flames (Cations):

  • Lithium makes a Crimson Red flame (Li+)
  • Sodium makes a Yellow Flame (Na+)
  • Potassium makes a Lilac flame (K+)
  • Calcium makes an Orange-Red flame (Ca2+)
  • Copper makes a Green flame (Cu2+)

  A) -

  
• FLAME Test for CATIONS (Metal Ions):

  • Dip a PLATINUM (or Nichrome) WIRE LOOP, in some DILUTE Hydrochloric Acid to clean it. Then RINSE it, and heat it over a Bunsen Burner
  • Dip the Wire Loop into the sample you want to test, and hold it in the CLEAR BLUE part of the Bunsen Burner (the HOTTEST part)
  • Record the colour in Flame

  A) -

  
• Test for HALIDES (Cl-, Br- and I-):

  • Add Dilute NITRIC Acid to the test tube, to remove any Impurities
  • Add SILVER NITRATE (AgNO3), so that the Silver Ions can react with one of the Halides to form a Precipitate

  Each Halide forms a DIFFERENT colour Precipitate:

  • Chloride (Cl-) forms a White Precipitate
  • Bromine (Br-) forms a Cream Precipitate
  • Iodide (I-) forms a Yellow Precipitate

  A) White

  B) Cream

  C) Yellow

  
• Test for SULFATES:

  • Add Dilute Hydrochloric Acid to the test sample, to REMOVE any Impurities
  • Then we can add the Barium Chloride solution (BaCl2)

  ---> If Sulphate Ions are present in the sample, you will see a WHITE Precipitate form in the tube

  • Because the Sulfate Ions react with Barium Chloride, to produce BARIUM SULFATE

  A) -