Cation precipitate tests (1 Viewer)

[Pandamonium99]

Hi All,

I have a chem. prac tomorrow on testing unknown cations in solution. We know that there will only be one cation per unknown sample.

What would be the best way of identifying the unknowns? Only problem with following the flowchart is that my school might not provide all the necessary things for each test... (e.g. NaF)

Any help would be appreciated!

 

[fan96]

Hydroxide precipitates are useful for identifying copper and both iron cations (especially for the latter if you aren't given thiocyanate or ferricyanide ions).

Your school should certainly have sodium hydroxide available.

is blue, is green, and is brown.

Lead will precipitate white with chloride (e.g. sodium chloride) and yellow with iodide.

If you have access to a bunsen, you can do a flame test for barium and calcium (but make sure the solution you are testing does not contain lead).

 

[Pandamonium99]

I thought that you the addition of NaOH to Fe2+ or Fe3+ would produce a brown precipitate (how would you differentiate between them?)

 

[fan96]

I thought that you the addition of NaOH to Fe2+ or Fe3+ would produce a brown precipitate (how would you differentiate between them?)

The iron (II) cation in hydroxide produces a GREEN precipitate - https://en.wikipedia.org/wiki/Iron(II)_hydroxide
The iron (III) cation in hydroxide produces a BROWN precipitate - https://en.wikipedia.org/wiki/Iron(III)_hydroxide

 

[HeroWise]

Flame tests can help too,

Strontium = scarlet
Lead = Prussian Blue
Potassium = lilac
Calcium = Carmine
etc

You can use ammonia and also Hydroxides to differentiate
Use solubility rules to see if prec will form or not