O Level Chemistry: Qualitative Analysis (QA) Tips


Below is a Table that can help us to identify cations in an unknown solution. This is very important in Qualitative Analysis Tests.

Besides SPA and Practical Examinations where the following table will be provided, you will need to memorize the table in order to answer QA questions that come out for Multiple-Choice Questions as well as Structured Questions.

But no fret, it is not that difficult to memorize it. Start by looking at Cu2+, Fe2+, Fe3+ and NH4+ because they have very distinct colours changes:

  • Cu2+ –> Blue PPT
  • Fe2+ –> Green PPT
  • Fe3+ –> Reddish Brown PPT
  • NH4+ –> Gives Pungent Ammonia Gas upon heating with NaOH
    identifying-cation.jpg (Click Image to have a better view)

PS: Do print a copy and paste it at the end of your notebook if necessary.

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2 Responses to O Level Chemistry: Qualitative Analysis (QA) Tips
  1. dona
    May 14, 2008 | 5:06 am

    ive discovered that when the substances react with NaoH, metal hydroxides r formed.those that are amphoteric react with excess NaoH causing the ppt to dissolve. therefore the ppt is sol. in xs. eg Pb2+, Al3+ & zn2+. correct me if im wrong

    Reply

  2. sean
    May 15, 2008 | 1:00 am

    You are right. These hydroxides are amphoteric in nature and will react with
    NaOH to form complexes that are soluble in water.

    Reply

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