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