Qualitative testing

• What is qualitative analysis?

  + uses simple test tube reaction observations instead of measurements e.g. gas bubbles, precipitates, colour changes
• How do you test for carbonate ions?

  + react with acids to produce carbon dioxide

  + add dilute HNO3 to carbonate in test tube

  + if bubbles of gas evolved/ given off this could be CO2

  + test gas by bubbling gas through limewater (saturated Ca(OH)2 solution)

  + CO2 reacts and forms a fine white precipitate CaCO3 and turns limewater cloudy (milky)
• How do you test for sulfate ions?

  + add small amount of barium chloride solution

  + milky white precipitate of barium sulfate formed, indicating presence of sulfate ions
• What is the test for identifying halide ions?

  + make solution of halide

  + acidify dilute nitric acid - prevents precipitation of other salts

  + add a few drops of silver nitrate solution

  + treat any precipitate with dilute/concentrated ammonia solution

  + if precipitate still exits, add concentrated ammonia solution
• How would you acidify the sample?

  + should add a few drops of dilute nitric acid to test the solution then add silver nitrate solution

  + prevents formation of other insoluble silver compounds e.g. silver carbonate

  + acid reacts with carbonate ions to form carbon dioxide gas

  + cannot use HCl as it contains chloride ions (gives white ppt with silver nitrate solution)

  + nitric acid contains nitrate ions -> nitrate compounds are soluble in water
• What is the further test to confirm the identity of halides present in solution?

  + adding ammonia solution

  + AgCl readily dissolves in dilute ammonia solution, silver bromide is soluble in concentrated ammonia solution and silver iodide is insoluble in concentrated ammonia solution
• What does the ammonia solution test for halides depend on?

  + relies on differences in solubility in ammonia between the three silver halide precipitates
• How do you test for the ammonium ion?

  + easily break down into ammonia gas

  + add NaOH

  + warm mixture and ammonia gas makes damp red litmus paper turn blue
• What is qualitative analysis used for?


  used to test for cations and anions in solution