Metal-air cells are a relatively new type of portable energy source consisting of a metal anode, an alkaline electrolyte paste that contains water, and a porous cathode membrane that lets in oxygen from the air. A schematic of the cell is shown above. Reduction potentials for the cathode and three possible metal anodes are given in the table below.
Half Reaction |
E at pH 11 and 298 K (V) |
O2(g) + 2 H2O(l) + 4 e− → 4 OH−(aq) |
+ 0.34 |
ZnO(s) + H2O(l) + 2 e− → Zn(s) + 2 OH−(aq) |
– 1.31 |
Na2O(s) + H2O(l) + 2 e− → 2 Na(s) + 2 OH−(aq) |
–1.60 |
CaO(s) + H2O(l) + 2 e− → Ca(s) + 2 OH−(aq) |
– 2.78 |
Early forms of metal-air cells used zinc as the Zinc oxide is produced as the cell operates according to the overall equation below.
2 Zn(s) + O2(g) → 2 ZnO(s)
A fresh zinc-air cell is weighed on an analytical balance before being placed in a hearing aid for
The zinc-air cell is taken to the top of a mountain where the air pressure is lower
Metal-air cells need to be lightweight for many In order to transfer more electrons with a smaller mass, Na and Ca are investigated as potential anodes. A 1.0 g anode of which of these metals would transfer more electrons, assuming that the anode is totally consumed during the lifetime of a cell? Justify your answer with calculations.
The only common oxide of zinc has the formula ZnO.
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