Dry cell chemistry (1 Viewer)

WEMG · Jan 15, 2011

I've seen many different cathode reactions for the Lelanche cell. The ones in Jacaranda and Conquering are both different and I'm not sure which one is correct.

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Zn + 2Mn4+ + 2O2- + 2NH4+ + 2Cl- -> Zn2+ + 2Cl- + 2Mn3+ + 3O2- + 2NH3 + H2O

This is the net ionic equation of the cell and in some notes, I've read that the Cl ion as well as the NH3 are spectator ions. I can see the Cl anion being a spectator ion but I dont see how NH3 is. In Jacaranda, the cathode half reaction still has NH3 but in some other sources NH3 is omitted.

Can someone clear this up for me?

nelsonzheng · Jan 15, 2011

If I'm not mistaken, the chemical reactions in this dry cell are much more complex than what is required by the HSC.
However, as stated in Wikipedia:

When the electrons enter the rod, they combine with manganese dioxide and water, which react with each other to produce manganese oxide and negatively charged hydroxide ions. This is accompanied by a secondary reaction in which the negative hydroxide ions react with positive ammonium ions in the ammonium chloride electrolyte to produce molecules of ammonia and water.

Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) → ZnCl2 + Mn2O3(s) + 2NH3(aq) + H2O

So according to that, NH3 is not a spectator ion, but are in fact a part of a secondary reaction, if that's what you were asking.

The reason why it is omitted in some equations is probably for the sake of simplification.

WEMG · Jan 16, 2011

Yeah I also read something like that but it was in someone elses notes so I wasnt sure it was completely right. Thanks for clearing it up for me.

313985971 · Jan 17, 2011

i just guessing
all i know is in this equation, the Zn lose electrons and Mn get electrons, and the other ions in this equation does not change their velocy so thats why the Cl, NH3 are spectators and as well as H2O and O.... thats all i was guessing.... by the way, u net equation is wrong, except the Cl, ur left hand side should only have One Oxygen ion and right hand side No Oxygen ion...here im apologising about my damn english.... if u dont understand what am saying ,just ignore it!!

Dry cell chemistry (1 Viewer)

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