Account for the following-i Transition metals show variable oxidation states-ii Zn- Cd and Hg are soft metals-iii E- value of the Mn3-Mn2- couple is highly positive - 1-57 V as compared to Cr3-Cr2-

(a) #160;Transition elements show variable oxidation #160;state due to #160;very small energy difference in (n 1)d and ns orbitals(b) #160;The electroni ...

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Byju's Answer

Standard XII

Chemistry

Electronic Configuration

Account for t...

Question

Account for the following:
(i) Transition metals show variable oxidation states.
(ii) $Z n, C d$ and $H g$ are soft metals.
(iii) $E^{\circ}$ value of the $M n^{3 +} / M n^{2 +}$ couple is highly positive $(+ 1.57 V)$ as compared to $C r^{3 +} / C r^{2 +}$

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Solution

(a) Transition elements show variable oxidation state due to very small energy difference in (n-1)d and ns-orbitals

(b) The electronic configurations of Zn, Cd and Hg are represented by the general formula (n-1)d¹⁰ns². The orbitals in these elements are completely filled in the ground state as well as in their common oxidation states

(c) $M n^{2 +}$ exists in $3 d^{5}$ configuration which is half filled configuration and such half filled configurations provide extra stability to the Metal Ion. While $M n^{3 +}$ will exist in $3 d^{4}$ configuration which is less stable than $3 d^{5}$ . Because of $3 d^{3}$ half filled d orbital extra stability is attained by $C r^{+ 3}$ than $C r^{+ 2}$ . hence $C r^{+ 3} \to C r^{+ 2}$ is less feasible.

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Q. (a) Account for the following:
(i) Transition metals show variable oxidation states.
(ii) Zn, Cd and Hg are soft metals.
(iii)

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M n^{3 +} / M n^{2 +}

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C r^{3 +} / C r^{2 +}

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Q. (a) Complete the following equations:
(i)

{C r}_{2} O_{7}^{2 -} + 2 O H^{-} \to

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M n O_{4}^{-} + 4 H^{+} + 3 e^{-} \to

(b) Account for the following:
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{M n}^{3 +} / {M n}^{2 +}

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{C r}^{3 +} / {C r}^{2 +}

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$C r^{2 +} / C r$	$- 0.9 V$ $	$C r^{3} / C r^{2 +}$	$- 0.4 V$
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