Question

How would you draw the galvanic cell for the reaction: Zn2+ + 4NH3 ---> [Zn(NH3)4]2+ Is this correct?

The textbook is showing these two half reactions.

I get a little confused when passive electrodes are involved in galvanic cells. It was not part of the question to draw the galvanic cells but its a concept that is expected in my course. And so thats why I was trying to visualize how it would look like in a galvanic cell.

Answer 1

Here's what I get.

Explanation:

The half-cell with the more negative reduction potential is the anode.

Then the half-cell reactions are:

`color(white)(mmmmmmmmmmmmmmmmmmmmmmmmmmmmmll)ul(E^@"/V")`
Anode: `color(white)(ll)color(red)(cancel(color(black)("Zn(s)"))) + "4NH"_3"(aq)" → "Zn"("NH"_3)_4^"2+""(aq)" + color(red)(cancel(color(black)("2e"^"-"))); color(white)(mmm)"+1.04"`
Cathode: `ul("Zn"^"2+""(aq)" + color(red)(cancel(color(black)("2e"^"-"))) → color(red)(cancel(color(black)("Zn(s)")))color(white)(mmmmmmmmm));color(white)(mmml) ul("-0.7618")`
Cell: `color(white)(mml)"Zn"^"2+""(aq)" + "4NH"_3"(aq)" → "Zn"("NH"_3)_4^"2+""(aq)"color(white)(ml);color(white)(mmm)"+0.28"`

You must make some changes to the diagram:

• The anode consists of zinc metal.

• The solution in the anode compartment contains aqueous ammonia and tetraamminezinc ion.

• Tetraamminezinc ions enter the solution from the anode surface as the zinc atoms become oxidized.

• The electrons do not move from the solution to the cathode. Instead, they move to the zinc through the external circuit.

• The zinc ions pick up the electrons at the surface of the cathode, where they become zinc atoms.