Role of sulfuric acid in gravity cells?
Salmon Egg
primary cell of choice well into the 20th century seems to be the Zn
anode, Cu cathode gravity cell. See Wikipedia among others. As far as I
can tell, during proper operation sulfuric acid in the electrolyte is
not used up. Zinc gets dissolved while copper gets plated out. This
copper plating frees up sulfate ion to move up from the bottom of the
cell to the top in order to maintain charge balance with the newly
created zinc ion. This leads me to a number of questions.
The advantage of the gravity cell is that no gas was evolved. That is
no hydrogen bubbles coated the cathode in a way that would increase
internal resistance. Additionally, using gravity to separate the
solutions removed the necessity of porous separators that would clog up
and give trouble.
1. What is the role of the sulfuric acid? Is it used to control pH.
2. Why does the pH need to be controlled. Is it to prevent
precipitation of Zn and Cu hydroxides?
3. What is the proper pH.
4. Is the pH uniform in the copper and zinc solutions? That is, are the
hydrogen (hydronium) ion able to move freely between the top and bottom?
5. I can understand why you would not want copper ion to reach and
plate out on the zinc anode. Does that depend primarily on gravity
between refurbishments of the cell? Is current flow significant in
keeping copper on the bottom?
6. What harm, if any, would there be if zinc ion moved into the copper
solution?
I have other questions as well. I am trying to understand some of these
details in order to improve my understanding of chemistry.
Bill
--
As the years go by, dying just before having to fill out a tax return has merit.