Question

The molten electrolytes contain $Na+,A{l}^{3+}$, and $C{a}^{2+}$ but only $Al$ gets deposited at the cathode because :

• A. standard reduction potential of $Al$ is more than that of $Na$ and $Ca$
• B. standard oxidation potential of $Al$ is less than that of $Na$ and $Ca$
• C. discharge potential of $A{l}^{3+}$ is higher than that of $N{a}^{+}$ and $C{a}^{2+}$
• D. discharge potential of $A{l}^{3+}$ is lesser than that of $N{a}^{+}$ and $C{a}^{2+}$

Answer 1

Answer: (A), (D)

The correct options are
A standard reduction potential of $Al$ is more than that of $Na$ and $Ca$
D discharge potential of $A{l}^{3+}$ is lesser than that of $N{a}^{+}$ and $C{a}^{2+}$

The Hall-Heroult process is used for the extraction of aluminum.

In electrolytic reaction, reduction takes place at cathode.

The standard reduction potential of metals is as follows:

$Ca=-2.87V$

$Na=-2.71V$

$Al=-1.66V$

The higher the standard reduction potential, the greater is the tendency of the metal ion to get reduced, i.e., the metal will get deposited easily on the cathode.

Out of $Al,Ca,Na$, aluminum has a higher reduction potential. Therefore, it will get deposited at the cathode.

In the electrolysis process, if two or more cations are present which can be ionized, then it is found that only a few cations are discharged at the electrodes.

The potential at which the ion is deposited or discharged on the electrode is called the discharge potential.

The decreasing order of discharge potential or increasing order of deposition is as follows :

$L{i}^{+}>K+>N{a}^{+}>C{a}^{2+}>A{l}^{3+}$

Since the discharge potential of aluminum is lower than $N{a}^{+}$ and $C{a}^{2+}$ metal ions, aluminum will be deposited at the cathode.

Hence, the correct options are (A) and (D).