To determine which substance will act as the cathode in a magnesium and zinc galvanic cell, it is essential to understand the roles of the metals and their ions in the electrochemical series and in redox reactions.
In a galvanic cell, the cathode is the electrode where the reduction reaction occurs. Reduction involves the gain of electrons. The metal that is less electropositive (more noble) will be reduced.
Magnesium (Mg) and zinc (Zn) have different tendencies to lose or gain electrons:
- Magnesium (Mg) has a higher tendency to lose electrons and form Mg²⁺ ions (it is more electropositive).
- Zinc (Zn) has less tendency to lose electrons compared to magnesium.
In a galvanic cell setup with these two metals, zinc is less likely to lose electrons than magnesium. Therefore, we need to identify the cathode by the process of reduction.
The magnesium ions (Mg²⁺) in the solution will not be the site of reduction because they are more likely to be oxidized to Mg metal. Instead, the zinc ions (Zn²⁺) in the solution will undergo reduction to form solid zinc (Zn(s)).
Thus, the cathode of the galvanic cell will be where the Zn²⁺ ions gain electrons and are reduced to solid zinc.
Therefore, the cathode in a magnesium and zinc galvanic cell is:
D. [tex]\( \operatorname{Zn}(s) \)[/tex]
