Confirmation Tests for Cations/Anions?

Question

I’m stuck on some problems for a lab report. Here are the questions, and my thinking on them so far:

A) Each of the following samples contains only one of the two chemicals indicated. What reagent would you use to identify which of the chemicals is present that you would use to distinguish between the two chemicals? Explain your choice.

1) Na2SO4 and NaI (Reagent: BaCl3 or FeCl3)

Leaning towards BaCl3, because it produces a precipitate with NaI only.

2) Fe(NO3)3 and Zn(NO3)2 (Reagent: NH3 or K4[Fe(CN)6])

NH3, because the other introduces Fe whether or not it is already present?

3) K3PO4 and Na2CO3 (Reagent: (NH4)2MoO4 or HCl)

I’m at a loss for this one.

B) How would you go about testing for the presence of SO4 in the presence of NO3?

Add a base first, or something else to react with the NO3 before you add the BaCl2, so that the Ba isn’t all used up in the formation of soluble barium nitrate. Maybe just excess BaCl2?

Tips and/or answers greatly appreciated!

Answer 1

A) 1)Na2SO4 and NaI (Reagent: BaCl3 or FeCl3)
BaCl3, To form precipitation BaSO4, whose solubility is extremely low.

2)Fe(NO3)3 and Zn(NO3)2 (Reagent: NH3 or K4[Fe(CN)6])
K4[Fe(CN)6]
Notice Fe(III) in Fe(NO3)3 and Fe(II) in K4[Fe(CN)6]. Fe(3+) added into K4[Fe(CN)6] forms Prussian blue:
http://en.wikipedia.org/wiki/Prussian_blue

3)K3PO4 and Na2CO3 (Reagent: (NH4)2MoO4 or HCl)
HCl.
Add HCl into Na2CO3 will generate bubbles due to:
2HCl(aq) + Na2CO3(aq) ==> 2NaCl(aq) + H2O + CO2(g)

B) How would you go about testing for the presence of SO4 in the presence of NO3?
Add Ba++ to form BaSO4(s).

Answer 2

Confirmatory Test For Anions