Question

(a) How do you prepare `:`
(i) `K_(2)MnO_(4)` from `MnO_(2)`
(ii) `Na_(2)Cr_(2)O_(7) ` from `Na_(2)CrO_(4)` ?

(b) Account for the following `:`
(i) `Mn^(2+)` is more stable than `Fe^(2+)` towards oxidation to `+3` state.
(ii) The enthalpy of atomisation is lowest for Zn in 3d series of transition elements.
(iii) Actinoid elements show wide range of oxidation states.
or (i) Name the elements of 3d transition series which shows maximum number of oxidation states. Why dows it show so ?
(ii)Which transition element of 3d series has positive `E_(M^(+)//M)^(@)` value and why ?
(iii) Out of `Cr^(3+)` and `Mn^(3+)` which is stronger oxidizing agent and why ?
(iv) Name a member of the lanthanoid series which is well known to exhibit `+2`oxidation state.
(v) Complete the equation `: ` `MnO_(4)^(-) +8 H^(+) + 5e^(-) rarr`

Answer 1

(i) Mn, (ii)Cu, (ii) `Mn^(3+)`, `(E_(M^(+)//Mn^(2+))^(@)= + 1.57V)`
(iv) `Eu^(2+)` due to exactly half filled `f^(7)` configuration and `Yb^(2+)` due to completely filled `f^(14)` configuration (v) `MnO_(4)^(-) +8 H^(+)+ 5e^(-) rarr Mn^(2+) 4H_(2)O)`