(a) Complete the following chemical equations : (i) MnO_(4)^(-)(aq)+S_(2)O_(3)^(2-)(aq)+H_(2)O(l)to (ii) Cr_(2)O_(7)^(2-)(aq)+Fe^(2+)(aq)+H^(+)(aq)to (b) Explain the following observations: (i) La^(3+) (Z = 57) and Lu^(3+) (Z = 71) do not show any colour in solutions. (ii) Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism. (iii) Cu^(+) ion is not known in aqueous solutions.

(a) Complete the following chemical equations : (i) MnO_(4)^(-)(aq)+S

1.	(a) Complete the following chemical equations : (i) MnO_(4)^(-)(aq)+S_(2)O_(3)^(2-)(aq)+H_(2)O(l)to (ii) Cr_(2)O_(7)^(2-)(aq)+Fe^(2+)(aq)+H^(+)(aq)to (b) Explain the following observations: (i) La^(3+) (Z = 57) and Lu^(3+) (Z = 71) do not show any colour in solutions. (ii) Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism. (iii) Cu^(+) ion is not known in aqueous solutions.
Answer» Solution :(a) (i) `8MnO_(4)^(-)(aq)+3S_(2)O_(3)^(2-)(aq)+H_(2)O(l)to 8MnO_(2) (s)+6SO_(4)^(2-)(aq)+2OH^(-)(aq)` (ii) `Cr_(2)O_(7)^(2-)(aq)+6Fe^(2+)(aq)+14H^(+)(aq)to2Cr^(3+)(aq)+6Fe^(3+)(aq)+7H_(2)O(l)` (b) (i) `La^(3+)` (Z = 57) and `Lu^(3+)`. (Z = 71) do not show any COLOUR in solutions. There is no f-electrons in `La^(3+)` and `Lu^(3+)`. HENCE, there is no possibility of f-f transition. Therefore, they show no colour in solution. (ii) `Mn^(2+)` has the `3d^(5)` CONFIGURATION. Thus, it has maximum (5) unpaired electrons. Therefore, it exhibits maximum paramagnetism. (iii) `Cu^(+)` ion undergoes disproportionation in AQUEOUS solution as under: `2Cu^(+)toCu^(2+)+Cu`