[Arkcon]

Not really no.  Typically, what's done is a small portion is left aside for certain tests, such as this one.  Also, if you will have an unknown anion, make sure it isn't one of the anions you've added for cation determination.  Even if you're sure, you should always keep some aside, as you add reagents, you dilute the unknown.  At some point, you will have a large volume of liquid.  Also, you should still stick to your addition procedure, because, in the case of multiple ions, you want to remove some so they don't react at the next steps.

You've also missed a very easy QA test for 3 of your ions.  Not that that's all that important, your procedure is well streamlined for your suspected cations.  Just wanted to make you look and see it, so you know there's something else out there, if you get a different set, some other time.

[Rutherford]

I know that I have to split the substance into few portions (thought about 4 for determining the cations and 4 for anions).
I had a tree-type procedure (adding HCl, H₂S, KI...), but I thought this way is much easier and faster and I had to split the substance into less portions.
No anions that I add, could be in the solution (CrO₄^2-, C₂O₄^2-, OH^-...). Didn't understand, can I swap step 2 and 4? And thanks for the help, it means a lot to me.

[Arkcon]

OK, you know that HCl is a rapid test for 3 cations -- Ag⁺, Pb²⁺, and Hg.  Just didn't want you to miss out on that one.  I wouldn't swap 2 and 4, step 4 should be done on a set aside portion ...  Nessler's Reagent, which is . wiki wiki wiki . potassium tetraiodomercurate in NaOH ... may be, at the very least, diluting your sample before step three.  When you do these sorts of procedures, you want to use complex reagents such as Nessler's very last.

[Rutherford]

So I can do step 1, 2 and 3 in the same portion and 4 in another one. Thanks again for the help.
Just a quickie for the anions:
CO₃^2-+HCl=bubbles
SO4^2-+Ba²⁺=unsoluble in almost anything
Cl^-+Ag⁺= white cheese precipitate soluble in NH₄OH
CH₃COO^-+acid(HCl, H₂SO₄...)=smell of CH₃COOH
The thoughest one: NO₃^-+H₂SO₄+FeSO₄=2 layers of liquid and a dark ring between them.
Is it ok?

[Arkcon]

Yes, I'd heard of that last one.  But I've never done it myself.  Ask the instructor if you can try that one out with a known solution to see if you have perfected the technique.

[AWK]

http://en.wikipedia.org/wiki/Nitrate_test

[Rutherford]

Thanks very much.

[Rutherford]

I add K₂CrO₄ (after the ion I will write the colour of the precipitate):
Ag⁺ red
Pb²⁺ dark yellow
Hg²⁺ orange
Cu²⁺ dark brown
Ba²⁺ light yellow

Can I add K₂Cr₂O₇ instead of K₂CrO₄? Will it make "completly" the same precipitates as CrO₄^2-?

[AWK]

-----Chromate - dichromate
Ag red-brown - brown-red (different colours)
Pb yellow ---------- yellow chromate
Hg orange -------- none
Cu red-brown ---- none
Ba yellow -------- none (chromate if CH₃COONa is added)

[Rutherford]

How to make chromate from dichromate because I can only use dichromate and I know how to determine the cations with chromate.

[AWK]

2Pb(NO₃)₂ + K₂Cr₂O₇ + H₂O = PbCrO₄ + 2KNO₃ + 2HNO₃
Nitric acid should be neutralized by sodium acetate to get complete precipitation.