InterviewSolution
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InterviewSolution
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(a)Complete the following chemical equations : (i) Cr_(2)O_(7)^(2-) (aq) + H_(2)S(g) + H^(+) (aq) rarr (ii)Cr^(2+) (aq)+I^(-) (aq) rarr (b) How wouldyou accound for the following? (i) The oxidizing power is the order :VO_(2)^(+) lt Cr_(2)O_(7)^(2-)lt MnO_(4)^(-) (ii) The thirdionization enthalpyofmanganese (Z= 25) is exceptionally high . (iii) Cr^(2+)is strongerreducting agentthan Fe^(2+). or (a) Complete the following chemical equations : (i) MnO_(4)^(-)(aq) +S_(2)O_(3)^(2-)(aq) + H_(2)O(l) rarr (ii)Cr_(2)O_(7)^(2-)(aq) + Fe^(2+) (aq) + H^(+)(aq) rarr (b)Explain the follwoing observations : (i) La^(3+) (Z= 57)and Lu^(3+) (Z= 71) do not show any colour in the solution. (ii) Among the divalentcations in the first series of transition elements, manganese exhibits the maximum paramagnetism (iii) Cu^(+) ion is notknown in aqueous solutions. |
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Answer» Solution :(a) (i) `Cr_(2) O_(7)^(2-) (aq) + 3H_(2)S(G) + 8H^(+)(aq) rarr 2Cr^(2+) (aq) +7H_(2)O(l) + 3S(s).`(ii)`2Cu^(2+)(aq) +4I^(-)(aq) rarr Cu_(2)I_(2)(s) +I_(2)(g)` (b) (i)This is due to increasing stability of the lower species to which they are reduced. (ii) Because 3rd electron has to be removed from stable half-filled3d-orbitals `(._(25)Mn= 3d^(5) 4s^(2))`. (iii)`E^(@) ( Cr^(3+) //Cr^(2+))-ve(0.41V) ,E^(@)(FE^(3+) //Fe^(2+))= +ve( +0.77V)` Hence, `Cr^(2+)` is easily oxidized to `Cr^(3+)` but `Fe^(2+)` cannot be easily oxidized to `Fe^(3+)`] or (a) (i)`8 MnO_(4)^(-)(aq) + 3S_(2)O_(3)^(2-)(aq) + H_(2)O(l) rarr 8 MnO_(2)(s) +6 SO_(4)^(2-) + 2OH^(-) (aq) ` (ii) `Cr_(2) O_(7)^(2-) (aq) +6Fe^(2+)(aq)+ 14H^(+)(aq) rarr 2Cr^(3+)(aq) + 6Fe^(3+) (aq) + 7H_(2)O(l)` (b)(i) Becaue they have completely filled 4f subshell. (II) `Mn^(2+)` has MAXIMUM number of unpairedelectrons. (iii) Because`Cu^(+)` in aqueous solution undergoes disproportionation `: 2 Cu^(+)(aq) rarr Cu^(2+)(aq) +Cu(s)` (as`E^(@)` value is favourable for this reaction ) ] |
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