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Jones reduction

  • Thread starter Big-Daddy
  • Start date
  • #1
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Homework Statement


Give the reactions that take place when the following solutions are passed through a Jones-redactor (amalgamated zinc), and calculate the equilibrium constant at 298.15 K for each.
0.01 mol/dm3 CuCl2
0.01 mol/dm3 CrCl3
0.01 mol/dm3 NH4VO3 (pH =1)

Data:
Couple, E° value
Cu2+/Cu 0.34
Cr3+/Cr –0.74
Cu2+/Cu+ 0.16
Cr2+/Cr –0.90
VO2+/VO2+ 1.00
Zn2+/Zn –0.76
VO2+/V3+ 0.36
TiO2+/Ti3+ 0.10
V3+/V2+ –0.255
Ag+/Ag 0.80
V2+/V –1.13
Fe3+/Fe2+ 0.77

Homework Equations



The usual equations - ΔG=-nFE, ΔG°=-nFE°, ΔG=-RTln(K).

The Attempt at a Solution



---

So one redox equation going on for all cases is the Zn2+/Zn couple, E°=–0.76, Zn2+ + 2e- ::equil:: Zn. The forward reaction will occur if E°[Zn2+/Zn]>E°[Couple j], where j is the couple which represents the redox equation occurring on the other side.

But how do I know which equation j will be, from all the different choices we get for each case? For example, in the first case, is it Cu2+ + e- -> Cu+, Cu+ + e- -> Cu, or Cu2+ + 2e- -> Cu which we need to consider as couple j against E°[Zn2+/Zn]? And how do we determine which equation we need to take for all three cases. I have seen the solutions but this question, of which one to choose of the possible equations, is not properly explained.
 

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