When a Zn rod is placed in $ZnSO_4$ solution, why does the oxidation not continue indefinitely at the same rate according to the notes?
AThe rod immediately dissolves completely
BA layer of excess positive charge builds up around the rod and opposes further oxidation
CSulfate ions deposit as metal on the rod
DZinc starts gaining electrons from the solution
Answer & Solution
Correct answer: B. A layer of excess positive charge builds up around the rod and opposes further oxidation
As zinc atoms leave the rod as $Zn^{2+}$, electrons remain on the rod, making it negative while the nearby solution becomes relatively positive. The notes say this excess positive charge forms a layer around the rod, which prevents further oxidation; this state is called the saturation point.
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