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Chemistry - Wizznotes

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									 Chemistry

Qualitative Analysis
What is qualitative analysis

 Qualitative analysis is used to determine the chemical
  composition of an unknown substance. Below is a list of
  some simple tests used to determine the presence of
  numerous anions and cations using the bench reagents
  present in the laboratory.
Test for carbonates and hydrogen carbonates


 Carbonates react with dilute acid with effervesce, liberating
  carbon dioxide.
 Test for carbon dioxide- carbon dioxide outs a lit wooden
  splint.
 Carbonates are present when a dilute acid is added to an
  unknown substance and carbon dioxide is liberated.
Test for the chloride and bromide ions


 chloride and bromide ions react with aqueous lead nitrate to
  form a white precipitate (ppt.)
 This ppt. dissolves when heated and solidifies when cooled.
Conformation of chloride ions (done after test for halides)

 Chlorides react with silver nitrate solution to form a white
  ppt.
 This ppt. then dissolves in a solution of aqueous ammonium
Test for the metal ions lead, zinc and aluminum


 Lead, zinc and aluminum ions react with aqueous sodium
  hydroxide to form a white ppt.
 White ppt. is soluble in excess sodium hydroxide.
Conformation of zinc ions (done after test for lead, zinc and
aluminum)

 Zinc ions react with aqueous ammonia to form a white ppt.
 Precipitate soluble in excess aqueous ammonia.
Conformation of aluminum ions (done after test for lead, zinc and
aluminum)

 Aluminum ions react with aqueous ammonia to form an
  white gelatinous ppt.
 Precipitate insoluble in excess aqueous ammonia.
Test for calcium ions


 Calcium ions form a white ppt. in aqueous sodium hydroxide
 Precipitate insoluble in excess aqueous sodium hydroxide.
Conformation of calcium ions (done after test for calcium)


 Add aqueous ammonia solution to an unknown solution until
  in excess-
 No ppt. formed.
Test for absence of lead and copper ions


 Add aqueous potassium iodide to an unknown solution
 No visible reaction.
Test for copper ions


 Copper ions react with aqueous sodium hydroxide to form a
  pale blue ppt.
 Insoluble in excess aqueous sodium hydroxide
Conformation of copper ions (done after test for copper)


 Copper ions react with aqueous ammonia to form a pale blue
  ppt.
 Precipitate dissolves in excess ammonia to form a dark blue
  solution
 Or add aqueous potassium iodide
 Dark brown ppt. formed (formation of the brown copper
  iodide).
Test for sulphate


 Sulphate ions react with barium chloride solution to form a
  white ppt.
 This ppt. is soluble in dilute HCl without effervescence
Test for nitrate


 Heat solid in test tube- colorless gas evolved followed by a
  pungent brown gas. Colorless gas relights a glowing wooden
  splint and brown gas turns damp blue litmus red.
 Colorless gas is oxygen
 Brown gas is NO2
Example of Qualitative Analysis


 Identify the ions in the unknown Z using the bench reagents.

								
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