Test for Cations (1 Viewer)

[Ragerunner]

for the test of FE2+ [ Iron(II) ]

"Every" textbook i have looked at has said a white precipitate forms and slowly turns brown when a NaOH solution is added to it.

however, i have done it for a prac and the results show it turns a greenish colour

anyone can confirm this ?

 

[spice girl]

that's because "slowly" means REALLY slowly

come back tomorrow and you'll see it brown...

 

[+:: $i[Q]u3 ::+]

i'm actually quite confused about this as well...
thickett and my prac sheets say that fe(oh)2 will be a pale greenish colour. and yes, my prac results showed it was green.
OTEN also says this in the shipwrecks option, where green
fe(oh)2 is oxidised in air to form rust.
is it just conq that says "white that slowly turns brown"?
at any rate, hsc markers can't mark us wrong if it's from a textbook.. and since conq says "whit turning brown", it's what i'm putting..

 

[freakofcool]

we had this discussion in class and the teacher said that it is green and that conq was wrong. we had an anion/cation assessment and i got the Fe2+ solution, which got the green and by the end of the lesson it was going brown! so it was definately and Fe2+ soln.

 

[Giant Lobster]

don't you add acidified potassium permanganate to Fe2+ soln and see if it is decolourised to test Fe2+?

I didnt know the OH method was actually a 'formal mark-earning' method...

 

[Exeter]

just add potassiumferricynaide in an acidic soln and it turns a deep deep prussian blue almost immediately

 

[Constip8edSkunk]

Originally posted by Exeter
just add potassiumferricynaide in an acidic soln and it turns a deep deep prussian blue almost immediately

But Fe3+ will give u a blue precipitate as well...


So what colour is Fe(OH)2 officially?

i got white, but didnt hav time 2 wait so im assuming it will, as Conquering and spice girlm, say SLOWLY turning Brown

But My Prac Sheet and Macquarie Uni says its white QUICKLY turning brown

Macmillan, CSU, and it seems alot of you got GREEN

Context doesnt even have the thing

guess i will just hav 2 use the decolourising permanganate 1...

 

[spice girl]

Originally posted by Constip8edSkunk
But Fe3+ will give u a blue precipitate as well...

test for Fe2+: add potassium hexacyanoferrate (K3[Fe(CN)6])
test for Fe3+: add potassium hexacyanoferrite (K4[Fe(CN)6])

positive test is deep blue

 

[Giant Lobster]

damn those compounds are complex.. Im sure there are many ways to test them.
I was taught Fe3+ is tested by adding sodium thiocyanate and it forms a deep red complex...

is there a right or wrong in regarding all these tests? most of which i never even heard about...

 

[Constip8edSkunk]

ok thanx for the correction (damn -ites -ates )

there r more ways than 1 to test the ions.