Valence States of Chromium and Silver in Net Ionic Equations: Which One to Use?

[greg153]

Homework Statement

I have to write a net ionic equation for Cr and silver nitrate, but I am confused on which valence state to use, since Cr has multiple valence states ie +2, +3 and + 6.2. The attempt at a solution
If I use the valence state of +2 I end up with:
Cr(s) + 2 Ag+(aq) = 2 Ag (s) + Cr2+(aq)

But if I use +3 I end up with:
Cr(s) + 3Ag+(aq) -> 3Ag(s) + Cr3+(aq)

So which one do I use? and is there a rule to follow?

Thanks.

 

[Borek]

In general you should compare potentials of half reactions. In this case go for Cr³⁺.

 

[greg153]

In general you should compare potentials of half reactions. In this case go for Cr³⁺.

Thanks borek. :)

Another quick question. Neither of these reactions would occur correct?

1.Au + HCl
No reaction since Au is below H2 in the activity series.

2.Ni + Ca(C2H3O2)2 (Ca acetate)
No reaction since Ni is below Ca in the activity series.

 

[Borek]

2xOK

 

[greg153]

Thanks.