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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4 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

  3. Sophia
    April 29, 2014 | 7:47 pm

    Hello! (: your tips on ‘QA- tests for cations’ really helped me! Do you happen to know any easy ways to remember the tests for anions? That would be a great help! (: thanks for taking the time to read my comment!

    Reply

    Sean Chua Reply:

    Thanks Sophia for your compliments.

    “Test for Anions” is in fact easier than the “Test for Cations” in my opinion.

    Cos there are only a few Anions they will test you on: Cl-, I-, NO3-, SO42- and CO32-.

    And the test for them are quite distinctive from the other (except that Cl- and I- have similar test and observations”.

    I will suggest that instead of memorising it, perhaps you want to understand the Chemistry of each test. In that way, you will find it easier to remember the tests.

    Enjoy learning Chemistry!

    Sean Chua

    Reply

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