Question

Which of the following reaction is possible at anode?

• A. $2Cr^{3+}+7H_{2}O \to Cr_{2}O^{2-}_{7} +14H^{+}$
• B. $F_{2} \to 2F^{-}$
• C. $\left(1/2\right)O_{2}+2H^{+} \to H_{2}O$
• D. None of these

Answer 1

Answer: (A)

The anode is the electrode where oxidation (loss of electrons) takes place; in a galvanic cell, it is the negative electrode, as when oxidation occurs, electrons are left behind on the electrode.
The cathode is the electrode where reduction (gain of electrons) takes place; in a galvanic cell, it is the positive electrode, as less oxidation occurs, fewer ions go into solution, and fewer electrons are left on the electrode.
So, in the reaction $2 Cr ^{3+}+7 H _{2} O \rightarrow Cr _{2} O _{7}^{2-}+14 H ^{+}$
Cr is getting oxidised as the oxidation state is changing from $+3$ to $+6$ and hence this reaction is possible at anode.