Question 12 Marks
Consider the standard electrode potential values $\left(\frac{M^{2+}}{M}\right)$ of the elements of the first transition series.
Explain:
i. $E^\circ$ value for copper is positive.
ii. $E^\circ$ value of $Mn$ is more negative as expected from the trend.
iii.$Cr^{3+}$ is a stronger reducing agent than $Fe^{2+}.$
| $Ti$ | $V$ | $Cr$ | $Mn$ | $Fe$ | $Co$ | $Ni$ | $Cu$ | $Zn$ |
| $-1.63$ | $-1.18$ | $-0.90$ | $-1.18$ | $-0.44$ | $-0.28$ | $-0.25$ | $+0.34$ | $-0.76$ |
Explain:
i. $E^\circ$ value for copper is positive.
ii. $E^\circ$ value of $Mn$ is more negative as expected from the trend.
iii.$Cr^{3+}$ is a stronger reducing agent than $Fe^{2+}.$
Answer
View full question & answer→i. The high energy to transform $Cu(s)$ to $Cu ^{2+}(aq)$ is not balanced by its hydration enthalpy.
ii. $Mn ^{2+}$ has $d ^5$ configuration $($stable half$-$filled configuration$)$
iii. $d ^5$ to $d ^3$ occurs in case of $Cr ^{2+}$ to $Cr ^{3+}. ($More stable $t_{2 g}^3 )$
while it changes from $d ^6$ to $d ^5$ in case of $Fe ^{2+}$ to $Fe ^{3+}$.
ii. $Mn ^{2+}$ has $d ^5$ configuration $($stable half$-$filled configuration$)$
iii. $d ^5$ to $d ^3$ occurs in case of $Cr ^{2+}$ to $Cr ^{3+}. ($More stable $t_{2 g}^3 )$
while it changes from $d ^6$ to $d ^5$ in case of $Fe ^{2+}$ to $Fe ^{3+}$.
