Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): $Cu ^{2+}$ in water is more stable than $Cu ^{+}$.
Reason (R): Enthalpy of hydration for $Cu ^{2+}$ is much less than that of $Cu ^{+}$.
In the light of the above statements, choose the correct answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. (A) is correct but (R) is not correct
• C. Both (A) and (R) are correct but (R) is not the correct explanation of $( A )$
• D. (A) is not correct but (R) is correct

Answer 1

Answer: (A)

$2 Cu ^{+} \rightarrow Cu ^{2+}+ Cu$
The stability of $Cu ^{2+}( aq )$ rather than $Cu ^{+}( aq )$, is due to the much more negative $\Delta_{\text {hyd }} H$ of $Cu ^{2+}$ (aq) than $Cu ^{+}( aq )$, which more than compensates for the second ionisation enthalpy of $Cu$.