11. Qualitative analysis

• What is precipitate?

  It is the insoluble salt produced when solutions are mixed
• How to test for cations?

  1. Place about 1.5 - 2cm^3 of the unknown solution into a test tube
  2. Add in a few drops of NaOH solution and shake after each drop
  3. Observe if any precipitate is formed
  4. If precipitate is formed, add excess NaOH solution
  5. Shake after adding to see if the precipitate is soluble or insoluble in excess
• How to test for certain cations?

  MEMORISE

  
• How to differentiate zinc from aluminium and lead ions?

  Add aqueous ammonia to differentiate zinc ions from aluminium or lead ions
• How to differentiate aluminum from lead ions?

  Add potassium iodide solution to unknown solution. If no ppt is formed, aluminium ion is present. If yellow ppt is formed, lead (II) ion is present
• How to test for certain anions?

  MEMORISE!

  
• Why must dilute nitric acid be added first in the test for sulfates, chlorides, and iodides anions?

  To react away other anions, such as carbonate, which might also give precipitates with the reagent and thereby giving a false positive result.
• How to test for certain gases?

  MEMORISE!

  
• What are the colours of common solids?

  MEMORISE!